JP3387072B2 - Exposure method and apparatus, and element manufacturing method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention corrects image forming characteristics or aligns a reticle and a wafer by using, for example, a statistical method, and transfers the pattern of the reticle to each shot area on the wafer sequentially. And an exposure method for a projection exposure apparatus.

[0002]

2. Description of the Related Art When manufacturing a semiconductor device or a liquid crystal display device by a photolithography process, a pattern image of a photomask or reticle (hereinafter referred to as "reticle") is coated with a photoresist through a projection optical system. A projection exposure apparatus for projecting each shot area on a wafer (or a glass plate or the like) is used. In recent years, as a projection exposure apparatus of this type, a wafer is placed on a stage that is two-dimensionally movable, and the wafer is stepped by this stage to form a pattern image of a reticle on each shot area on the wafer. A so-called step-and-repeat type exposure apparatus, for example, a reduction projection type exposure apparatus (stepper), which repeats the operation of sequentially performing exposure is frequently used.

For example, since a semiconductor element is formed by stacking a large number of circuit patterns on a wafer, when projecting and exposing the circuit patterns of the second and subsequent layers, the circuit patterns are already formed on the wafer. It is necessary to accurately perform alignment between each shot area thus formed and the pattern image of the reticle to be exposed, that is, alignment. As a conventional method for aligning a wafer in a stepper or the like, there is known an enhanced global alignment (hereinafter referred to as "EGA") system as described below (see, for example, JP-A-61-44429).

That is, a chip pattern including alignment marks (alignment marks) is formed on each of a large number of shot areas regularly arranged on a wafer to be processed on the basis of preset arrangement coordinates. Are formed. However, when another pattern is overlaid on the formed pattern, even if the wafer is stepped on the basis of the set array coordinates, a satisfactory overlay accuracy is not always obtained due to the following factors.

(1) Remaining rotation error of wafer Θ (2) Orthogonality error of stage coordinate system (or shot array) W (3) Linear expansion / contraction of wafer Rx, Ry (4) Offset of wafer (center position) (parallel) Move) O _X ,
O _Y

Since these four error amounts can be represented by 6 parameters, a conversion matrix A of 2 rows × 2 columns consisting of elements represented by 4 parameters among them, and an offset (parallel movement) ) Consider a conversion matrix O of 2 rows × 1 column having O _X and O _Y as elements. Then, the designed array coordinate values (D _Xn , D _Yn ) of each shot area on the wafer (n = 0, 1,
2, ...) and the actual array coordinate values (F _Xn , F _Yn ) to be aligned by the step-and-repeat method are expressed by using the conversion matrices A and O as follows. And

[0007]

[Equation 1]

At this time, array coordinate values (F) obtained by actually measuring a plurality of shot areas selected on the wafer
M _Xn , FM _Yn ) and the calculated array coordinate values (F _Xn , based on (Equation 1)) for the corresponding shot area.
The transformation matrices A and O are determined by using the least square method so that the average deviation from F _Yn ) is minimized. Then, conventionally, on the basis of the determined conversion matrices A and O and the designed array coordinate values (D _Xn , D _Yn ), from the above (Formula 1), a position to be actually aligned is calculated. Array coordinate value (F
_Xn , F _Yn ) was calculated, and each shot area of the wafer was positioned based on the calculated coordinate values.

[0009]

However, the array coordinate values (F _Xn ,
Even if the wafer is aligned based on F _Yn ), if rotation or offset (parallel movement) occurs on the pattern side of the reticle, the pattern image of the reticle and the chip pattern of each shot area on the wafer become There is the inconvenience of not overlapping exactly.

For this reason, conventionally, for example, an alignment microscope is used to detect the positioning accuracy of the pattern of the reticle, and exposure is performed in a state where the positioning accuracy is within a predetermined allowable range. However, in this method, it is necessary to repeat the complicated work every time the reticle is exchanged, and there is a disadvantage that the throughput of the exposure process is reduced.

Conventionally, the projection magnification of the projection optical system was considered to be the designed value. However, in reality, the pattern of the reticle is affected by an error in the projection magnification of the projection optical system, a drawing error in the reticle pattern, or the like. There is a possibility that the magnification of the projected image through the projection optical system of 1 is out of the designed value. Although such an error amount is extremely small and has not been regarded as a problem in the past, it is required to be smaller as the semiconductor element to be manufactured is further miniaturized. .

In view of the above problems, the present invention is capable of efficiently obtaining the rotation of the reticle on the pattern side, etc., and improving the alignment accuracy between the reticle and the wafer and performing exposure with high throughput. It is an object to provide a method and a device . It is another object of the present invention to provide an exposure method and apparatus that can directly measure the magnification of a projected image of a reticle and can improve the overlay accuracy of a reticle pattern image and a wafer.

[0013]

According to a first exposure method of the present invention, a mask on which an exposure pattern is formed is illuminated, and the pattern of the mask is first coordinated through a projection optical system (PL). In an exposure method of projecting and exposing on a photosensitive substrate (8) positioned on a system (X, Y), a plurality of position detection marks together with an exposure pattern (41) on the mask as the mask Using the mask (2) for actual exposure on which (43A to 43H) are formed, the marks for position detection on the mask for actual exposure, which are positioned on the second coordinate system (ξR, ηR), are detected. Projection optical system (P
L) the first step (step 1) of detecting the position of the images (43AW to 43HW) on the first coordinate system (X, Y).
03).

Further, according to the present invention, the conventional EGA method is applied to convert the image of the position-detecting marks detected in the first step into a two-dimensional mark.
A first coordinate system in which the substrate (8) is positioned from the coordinates on the second coordinate system (ξR, ηR) on the mask (2) for actual exposure by statistically calculating the positions of at least one image. (X,
Y) has a second step (step 104) of obtaining a conversion parameter for coordinates, and adjusts the imaging state of the projection optical system (PL) based on the conversion parameter obtained in this second step, and After the actual exposure mask (2) and the substrate (8) are positioned, the exposure pattern (41) of the actual exposure mask (2) is exposed on the substrate (8).

In this case, the state of the substrate (8) is further changed to EGA.
It is desirable to measure by the method. That is, the plurality of processed regions (27) arranged on the substrate (8) based on the arrangement coordinates on the third coordinate system (α, β) set on the substrate (8).
-I), measuring the coordinate position on the first coordinate system (X, Y) of at least three preselected sample areas (step 107), and statisticizing the plurality of coordinate positions thus measured. By calculating, a conversion parameter from the coordinate on the third coordinate system (α, β) on the substrate (8) to the coordinate on the first coordinate system (X, Y) is calculated (step 108), Based on the conversion parameters from the third coordinate system (α, β) to the first coordinate system (X, Y) and the conversion parameters obtained in the second step, the projection optical system (P
After adjusting the image forming state of (L) (step 110) and positioning the mask (2) for actual exposure and the substrate (8) (steps 109, 110), the mask (2) for actual exposure.
It is desirable to expose the pattern for exposure of the above onto the substrate (8). A second exposure method according to the present invention is an exposure method of illuminating a mask on which an exposure pattern is formed and projecting and exposing the mask pattern onto a substrate through a projection optical system. The actual exposure mask in which a plurality of position detection marks are formed together with the exposure pattern on the mask is used.
Before exposing the mask pattern onto the substrate,
By performing a statistical calculation using the first step of detecting the position information regarding the plurality of position detection marks formed on the exposure mask and the position information detected in the first step, A second step of obtaining an error parameter,
A third step of controlling the image forming characteristic of the projection optical system based on the error parameter obtained in the second step,
Is to have. A third exposure method according to the present invention illuminates a mask on which an exposure pattern is formed,
In an exposure method in which the pattern of the mask is projected and exposed on a substrate through a projection optical system, an actual exposure mask on which a plurality of position detection marks are formed together with the exposure pattern on the mask is used as the mask. Along with
The mask pattern for the actual exposure of
Before, the plurality of position detection marks formed on the mask for the actual exposure, the first step of detecting the positional information of the image through the projection optical system, is detected in the first step And a second step of obtaining a plurality of error parameters by performing statistical calculation using the position information. Further, the element manufacturing method according to the present invention includes a step of projecting a circuit pattern for forming a semiconductor element or a liquid crystal display element onto a substrate using any of the exposure methods of the present invention. Next, a first exposure apparatus according to the present invention is an exposure apparatus that illuminates a mask on which an exposure pattern is formed and projects the pattern of the mask onto a substrate through a projection optical system. As the mask, an actual exposure mask in which a plurality of position detection marks are formed together with the exposure pattern on the mask is used.
Before exposing the pattern of the mask for actual exposure on the substrate
In, by performing a statistical calculation using the detection means for detecting the position information regarding the plurality of position detection marks formed on the mask for actual exposure, and the position information detected by the detection means, It has an arithmetic means for obtaining a plurality of error parameters and a control means for controlling the imaging characteristics of the projection optical system based on the error parameters obtained by the arithmetic means. A second exposure apparatus according to the present invention is an exposure apparatus that illuminates a mask on which an exposure pattern is formed and projects and exposes the pattern of the mask onto a substrate via a projection optical system. using a mask for actual exposure of detection mark a plurality of positions are formed with an exposure pattern on the mask as
Together with the pattern of the mask for this actual exposure on the substrate
Formed on the mask for this actual exposure before exposure
Are marks for a plurality of position detection, by performing a detection means for detecting the position information of the image through the projection optical system, a statistical calculation using the position information detected by the detection means, a plurality of error And a calculating means for obtaining a parameter.

[0016]

According to the present invention, as shown in FIG. 4A, the mask (2) for actual exposure has the coordinate system (ξR, ηR).
Position detection marks (43A to 43H) each representing a two-dimensional position are formed on the top. The image of the mask (2) is projected onto the stage on which the substrate (8) is placed via the projection optical system (PL). Then, as shown in FIG. 5, the projected images (43
The positions of, for example, three or more projected images on the first coordinate system (X, Y) are detected from among AW to 43HW). As a detection method, a slit plate and a photoelectric detector provided on a stage on which the substrate (8) is placed are arranged in the first coordinate system (X,
Y) a method of scanning to detect the position of each projected image, or scanning the stage while the slit pattern image is projected from the stage side on which the substrate (8) is mounted to the mask (2) side, From the amount of light transmitted through the mask (2), the projected image (4
3AW to 43HW).

In general, the coordinate system (ξR,
The conversion equation from the coordinate on ηR) to the coordinate on the first coordinate system (X, Y) that defines the position of the substrate (8) should be expressed by using six conversion parameters as in (Equation 1). You can The values of these six conversion parameters can be easily obtained by applying the conventional EGA method. That is, 2
In the case of a dimensional mark, three or more projected images (43AW-43AW
The six conversion parameters are obtained by detecting the position of (HW) and using the least squares method. The six conversion parameters are the rotation of the mask (2), the magnification error in two directions of the projected image (including the magnification error of the projection optical system (PL) itself), and the orthogonality of the coordinate system (ξR, ηR). It represents the error and the offset in two directions. Then, for example, by correcting the position of the mask (2) or the substrate (8) so as to reduce the rotation and offset of the mask (2),
The alignment accuracy between the mask (2) and the substrate (8) is improved.

Since the magnification error of the projected image itself is directly obtained, for example, the mask (2) is formed on the first layer of the substrate (8).
When exposing the pattern image of, the projection magnification of the projection optical system (PL) is corrected by, for example, a method of moving a lens element forming the projection optical system (PL), and the magnification of the projection image is set to a design value. To match. On the other hand, when exposing the second layer of the substrate (8), the magnification error of the circuit pattern already formed on the second layer is measured, and the mask (2) is applied to the magnification error of the circuit pattern. Match the magnification error of the projected image of.

Next, the third coordinate system (α,
When the conversion parameters from β) to the first coordinate system (X, Y) are also obtained by the EGA method, for example, the rotation of the mask (2), the magnification, etc. and the rotation of the substrate (8), the magnification, etc. are the same. Required to. Therefore, for example, by adjusting the rotation angle of the mask (2) to the rotation angle of the substrate (8), the alignment accuracy and the overlay accuracy of the mask (2) and the substrate (8) can be improved.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In this example, the present invention is applied to an exposure process of an exposure apparatus (stepper) that exposes a reticle pattern to each shot area on a wafer as a photosensitive substrate by a step-and-repeat method.

FIG. 2 shows the exposure apparatus of this example. In FIG. 2, the exposure light IL emitted from the illumination optical system 1 illuminates the reticle 2 with a substantially uniform illuminance. The reticle 2 is held on a reticle stage 3, and the reticle stage 3 is supported so as to be movable and minutely rotatable within a two-dimensional plane on a base 4. A main control system 6 that controls the operation of the entire apparatus controls the operation of the reticle stage 3 via a drive device 5 on the base 4.

Under the exposure light IL, the pattern image of the reticle 2 is projected onto each shot area on the wafer 8 via the projection optical system PL. The wafer 8 is placed on the wafer stage 10 via the wafer holder 9. The wafer stage 10 is an XY stage that two-dimensionally positions the wafer 8 in a plane perpendicular to the optical axis AX of the projection optical system PL, and a Z stage that positions the wafer 8 in a direction parallel to the optical axis AX (Z direction). , And a stage for rotating the wafer 8 minutely.

A photoelectric sensor 7 is fixed near the wafer 8 on the wafer holder 9 (or the uppermost stage of the wafer stage 10). The photoelectric sensor 7 is
A photoelectric detector for photoelectrically converting the light flux transmitted through the slit plate is arranged under the slit plate formed with slits having the same pattern as the bright portion of the projected image of the alignment mark (described later) formed on the reticle 2. The surface of the slit plate is set at the same height as the exposure surface of the wafer 8. The output signal of the photoelectric detector in the photoelectric sensor 7 is supplied to the main control system 6. In this embodiment, the position of the projection image of the alignment mark formed on the reticle 2 is measured by scanning the photoelectric sensor 7 in a plane perpendicular to the optical axis AX of the projection optical system PL.

A movable mirror 11 is fixed on the upper surface of the wafer stage 10, and a laser interferometer 12 is arranged so as to face the movable mirror 11. Although shown in a simplified manner in FIG. 2, the movable mirror 11 has an X-axis and a Y-axis as an orthogonal coordinate system in a plane perpendicular to the optical axis of the projection optical system 7.
It is composed of a plane mirror having a reflection surface perpendicular to the axis and a plane mirror having a reflection surface perpendicular to the Y axis. Further, the laser interferometer 12 includes two laser interferometers for X-axis that irradiate the moving mirror 11 with a laser beam along the X-axis and a Y-axis for irradiating the moving mirror 11 with a laser beam along the Y-axis. The laser interferometer is used for measuring the X coordinate and the Y coordinate of the wafer stage 10 with one laser interferometer for the X axis and one laser interferometer for the Y axis. The coordinate system (X, Y) composed of the X coordinate and the Y coordinate measured in this way is hereinafter referred to as a stage coordinate system or a stationary coordinate system.

Further, the rotation angle of the wafer stage 10 is measured by the difference between the measured values of the two laser interferometers for the X axis. X coordinate, Y measured by laser interferometer 12
Information on coordinates and rotation angle is supplied to the coordinate measuring circuit 12a and the main control system 6, and the main control system 6 monitors the supplied coordinates and drives the wafer stage 10 via the drive unit 13.
Control the positioning operation of. Although not shown in FIG. 2, the reticle side is also provided with the same interferometer system as the wafer side.

The projection optical system PL of this example is equipped with an image forming characteristic control device 14. The imaging characteristic control device 14 adjusts, for example, the interval between predetermined lens groups of the lens groups that form the projection optical system PL, or adjusts the pressure of gas in the lens chamber between the predetermined lens groups. Thus, the projection magnification and the distortion of the projection optical system PL are adjusted. The operation of the imaging characteristic control device 14 is also controlled by the main control system 6.

In this example, the side surface of the projection optical system PL is turned off.
An axis type alignment system 15 is arranged, and in this alignment system 15, the illumination light from the light source 16 passes through a collimator lens 17, a beam splitter 18, a mirror 19 and an objective lens 20 and is near an alignment mark 29 on the wafer 8. Is irradiated. In this case, the baseline amount, which is the distance between the optical axis 20a of the objective lens 20 and the optical axis 7a of the projection optical system 7, is measured in advance. Then, the reflected light from the alignment mark 29 is irradiated onto the index plate 22 via the objective lens 20, the mirror 19, the beam splitter 18 and the condenser lens 21, and the index plate 2
An image of the alignment mark 29 is formed on the surface 2.

The light transmitted through the index plate 22 passes through the first relay lens 23 toward the beam splitter 24, and the light transmitted through the beam splitter 24 is transmitted through the X-axis second relay lens 25X to the X-axis composed of a two-dimensional CCD. Is focused on the image pickup surface of the image pickup device 26X for use in the beam splitter 2
The light reflected at 4 is focused on the image pickup surface of the Y-axis image pickup device 26Y including a two-dimensional CCD by the Y-axis second relay lens 25Y. An image of the alignment mark 19 and an image of the index mark on the index plate 22 are superimposed and formed on the image pickup surfaces of the image pickup devices 26X and 26Y, respectively. The image pickup signals of the image pickup devices 26X and 26Y are both coordinate position measurement circuit 1
2a.

FIG. 3 shows the pattern on the index plate 22 of FIG. 2. In FIG. 3, an image 29P of the cross-shaped alignment mark 29 is formed in the central portion, and a linear pattern image 29XP of the image 29P intersecting at right angles is formed. 2 and 29YP are respectively in conjugation with the X and Y directions of the stage coordinate system of the wafer stage 10 shown in FIG. Then, the two index marks 31A and 31 are arranged so as to sandwich the alignment mark image 29P in the XP direction.
B is formed, and two index marks 32A and 32B are formed so as to sandwich the alignment mark image 29P in the YP direction.

In this case, the index marks 31A,
31B and the detection area 33 surrounding the linear pattern image 29XP
The image in X is picked up by the X-axis image pickup device 26X in FIG.
The image in the detection area 33Y surrounding the index marks 32A and 32B and the linear pattern image 29YP in the P direction is imaged by the Y-axis image sensor 26Y in FIG. Furthermore, the scanning directions when reading photoelectric conversion signals from the pixels of the image pickup devices 26X and 26Y are set to the XP direction and the YP direction, respectively, and by processing the image pickup signals of the image pickup devices 26X and 26Y,
Alignment mark image 29P and index marks 31A, 31
It is possible to obtain the amount of positional deviation between B and 32A, 32B in the XP and YP directions. Therefore, in FIG.
The coordinate measuring circuit 12a determines the stage coordinate system (X) of the alignment mark 29 based on the positional relationship between the image of the alignment mark 29 on the wafer 8 and the index mark on the index plate 22 and the measurement result of the laser interferometer 12 at that time. , Y), and the coordinate values thus measured are supplied to the main control system 6.

Now, the pattern of the reticle 2 used in this embodiment will be described. FIG. 4A shows the reticle 2 of this embodiment, and in FIG. 4A, a circuit pattern 41 for exposure is formed in the central portion of the reticle 2.
Then, around the circuit pattern 41 and in the projection optical system P.
8 inside the area 42R conjugate with the effective exposure field of L
The same alignment marks 43A to 43H are formed. The positions of these alignment marks 43A to 43H are predetermined on the orthogonal coordinate system (ξR, ηR) with the center of the reticle 2 as the origin (0, 0). Although not shown, the alignment mark 4 is formed on the reticle 2.
In addition to 3A to 43H, alignment marks for positioning the reticle 2 on the reticle stage 3 are also formed.

FIG. 4B shows the shape of the alignment mark 43A. In this FIG. 4B, the alignment mark 43A is a line composed of opening patterns arranged at a predetermined pitch in the ξR direction with the light shielding film 44 as the background. The AND and space pattern 45 and the line and space pattern 46 composed of opening patterns arranged at a predetermined pitch in the ηR direction are formed. The line and space patterns 45 and 46 specify the positions of the alignment mark 43A in the ξR direction and the ηR direction, respectively. Other alignment marks 43B ~
43H also has the same shape.

The slit plate of the photoelectric sensor 7 shown in FIG. 2 has the line-and-space pattern 4 shown in FIG. 4B.
A pattern conjugate with 5 and 46 is formed. next,
With reference to the flowchart of FIG. 1, the wafer 8 is used in this embodiment.
The operation of aligning each of the above shot areas with the pattern image of the reticle 2 and exposing each shot area will be described. First, in step 101 in FIG. 1, the reticle 2 is loaded on the reticle stage 3 in FIG. 2, and in step 103, the reticle 2 is aligned. For this purpose, for example, an alignment microscope (not shown) arranged above the end portion of the reticle 2 in FIG. 2 is used, and the alignment marks (alignment marks 43A to 43H in FIG. 4A) different from the alignment marks on the reticle 2 are used. The position of the mark) is detected, and the reticle 2 is positioned so that the position becomes a predetermined position.

Next, in step 103, the wafer stage 1 having three or more alignment marks among the eight alignment marks 43A to 43H on the reticle 2
The coordinates of the projected image on 0 in the stage coordinate system (X, Y) are measured. FIG. 5 shows projected images of the alignment marks 43A to 43H of the reticle 2 shown in FIG. 4A on the wafer stage 10. In FIG. 5, the projection optical system PL is shown.
Eight alignment mark images 43AW to 43HW are projected in the effective exposure field 42 of FIG. Further, when the imaging state of the projection optical system PL is ideal, the projected image of the coordinate system (ξR, ηR) on the reticle 2 onto the wafer stage 10 is represented by the coordinate system (ξ, η). . In this embodiment, the designed array coordinates (CRξ) of the alignment marks 43A to 43H on the reticle 2 coordinate system (ξR, ηR).
_Xn , CRη _Yn ) (n = 1 to 8) is set on the wafer stage 10
Alignment mark image 43 on the upper coordinate system (ξ, η)
Sequence coordinates AW~43HW (CR _Xn, CR _Yn) is converted to. Then, the array coordinates of the alignment mark images 43AW to 43H in the stage coordinate system (X, Y) are (FR _Xn , F).
R _Yn ).

In this case, the reticle 2 has the following error factors with respect to the stage coordinate system (X, Y).
The array coordinates (CR _Xn , CR _Yn ) are array coordinates (FR _Xn , FR
_Yn ) does not match.

Rotation of reticle: This is represented by the residual rotation error Θ _R of the coordinate system (ξ, η) converted to the wafer side of the reticle with respect to the stage coordinate system (X, Y). Orthogonality of the reticle coordinate system (ξ, η): This is the error in which the patterns in the ξ-axis direction and the η-axis direction are not exactly orthogonal due to drawing errors, and is represented by the orthogonality error W _R.

Ξ in the reticle coordinate system (ξ, η)
Direction and η direction magnification error: This is an error caused when the pattern length of the reticle 2 has an error or when the projection magnification of the projection optical system PL deviates from a design value (for example, 1/5). . This error is represented by magnification errors RRx and RRy in the ξ direction and the η direction, respectively.
However, the magnification error RRx in the ξ direction is the ratio between the measured value and the design value of the distance in the ξ direction between the two alignment mark images on the wafer stage, and the magnification error RRy in the η direction is the η direction between the two alignment mark images. It shall be expressed by the ratio of the measured value of the interval of and the design value. Stage coordinate system (X, η) of reticle coordinate system (ξ, η)
Offset with respect to Y): This is caused by the projection image of the reticle 2 deviating from the wafer stage 10 by a slight amount, and is represented by offset errors OR _X and OR _Y.

When the error factors (1) to (3) above are added,
The coordinate (F, X) of the alignment mark image whose design coordinate value is (CR _Xn , CR _Yn ) on the stage coordinate system (X, Y)
R _Xn , _FRYn ) is expressed as follows.

[0039]

[Equation 2]

Here, if the linear approximation is performed assuming that the orthogonality error W _R and the residual rotation error Θ _R are minute amounts, (Equation 2)
Is as follows.

[0041]

[Equation 3]

Next, the matrix and vector of (Equation 3) are replaced with the matrix FRn, AR and the vector CRn, OR as follows.

[0043]

[Equation 4]

As a result, (Equation 3) is expressed as follows.

[0045]

[Equation 5]

Four errors (hereinafter, also referred to as "error parameter") RRx, R in the matrix AR in (Equation 5)
The purpose is to find Ry, W _R , Θ _R and two offset errors (error parameters) OR _X , OR _Y in the vector OR. For this purpose, the calculation method of the EGA method for calculating the wafer shot arrangement is used. Can be applied. That is, since there are six error parameters to be obtained, the coordinates in the stage coordinate system (X, Y) of three or more alignment mark images from the alignment mark images 43AW to 43HW in FIG. 5 are obtained and measured. The sum of squares (residual error component) between the calculated coordinates and the calculated coordinates determined by (Equation 5) may be minimized.

The alignment mark image 43A shown in FIG.
W to 43HW are two-dimensional marks in which two one-dimensional marks are combined, so three or more are measured,
When only one-dimensional marks are selected, it is necessary to measure the positions of six or more marks. Further, it is a condition that three or more alignment mark images selected from the alignment mark images 43AW to 43HW in FIG. 5 are not located on the same straight line. Further, it is desirable that the alignment mark image to be measured be distributed so as to be substantially point-symmetric with respect to the optical axis without being biased within the effective exposure field 42 of the projection optical system PL.

Therefore, in step 103, as shown by hatching in FIG. 5, for example, four alignment mark images 43BW, 43D which are substantially point symmetric with respect to the optical axis.
The array coordinates in the stage coordinate system (X, Y) of W, 43FW, 43HW are measured. At this time, the photoelectric sensor 7 of FIG. 2 may be scanned in the XY plane to find the positions where the photoelectric conversion signals have respective maximum values. Then, step 104
In the above, the six error parameters (RRx, RRy, W _R , Θ _R , which satisfy (Equation 5) by the above-mentioned least squares method,
The value of OR _X , OR _Y ) is calculated.

Although the above-mentioned method applies the normal EGA method, the measurement data of the alignment mark image of FIG. 5 is weighted according to the distance from the center of the reticle 2, for example. The six error parameters may be obtained by a so-called weighted EGA method. The weighted EGA method will be described later. Also,
In some cases, the orthogonality error W _R is ignored (assumed to be 0), and the magnification errors RRx and RRy are shared by the average value R.
It may be replaced with R (= (RRx + RRy) / 2). In this case, the matrix AR of (Equation 5) can be approximated as follows.

[0050]

[Equation 6]

Under this approximation, since the number of error parameters to be obtained is 4, the number of alignment mark images to be measured in order to apply the least square method is 2 or more in the case of a two-dimensional mark. Get better in Next, in this embodiment, the rotation, linear expansion and contraction of the wafer are measured by a method that is an extension of the conventional EGA method. The method will be described below.

FIG. 6A shows the wafer 8 of this embodiment,
In FIG. 6A, a plurality of shot areas 27-n (n = n) are formed along the orthogonal coordinate system (α, β) on the wafer 8.
, 1, ... Are arranged in a matrix, and chip patterns are formed in each shot area 27-n by exposure and development in the previous step. In FIG. 6A, five shot areas 27 among the plurality of shot areas 27 are shown.
Only -1 to 27-5 are shown as a representative.

A reference position is defined for each shot area 27-n. For example, when the reference position is the reference point 28-n at the center of each shot area 27-n, the design coordinate values of this reference point 28-n in the coordinate system (α, β) on the wafer 8 are ( C _Xn , C _Yn ). In addition, four alignment marks 29- for alignment are provided in each shot area 27-n.
n, 30-n, 34-n, and 35-n are provided together. In this case, each shot area 27-n is formed in parallel with the coordinate system (α, β) on the wafer of FIG.
Coordinate system (x, y) on the shot area as shown in (b)
Is set, the alignment marks 29-n, 30-
n, 34-n, 35- n coordinate system (x, y) on each coordinates of the design in the _{(S 1Xn, S 1Yn),} (S 2Xn, S
_2Yn ), ( _S3Xn , _S3Yn ) and ( _S4Xn , _S4Yn ).

Returning to FIG. 6A, the wafer 8 is placed on the wafer stage 10 of FIG. 2, and the reticle is projected onto each of a plurality of shot areas in which chip patterns have already been formed by the step-and-repeat method. Exposure is performed by sequentially superimposing images. At this time, the correspondence relationship between the stage coordinate system (X, Y) that defines the moving position of the wafer stage 10 and the wafer coordinate system (α, β) is not necessarily the same as the relationship in the previous step. Therefore, from the design coordinate values (C _Xn , C _Yn ) of the reference point 28-n of each shot area 27-n with respect to the coordinate system (α, β), the stage coordinate system (X,
Even if the coordinates on Y) are obtained and the wafer is moved based on these coordinates, the shot areas 27-n may not be precisely aligned. Therefore, in the present embodiment, first, it is assumed that the alignment error is caused by the following four factors as in the conventional example.

Wafer rotation: This is represented by the residual rotation error Θ of the wafer coordinate system (α, β) relative to the stage coordinate system (X, Y). Orthogonality of stage coordinate system (X, Y): This occurs because the feed of the wafer stage 10 in the X-axis direction and the Y-axis direction is not exactly orthogonal, and is represented by an orthogonality error W.

Linear expansion and contraction in the α and β directions in the wafer coordinate system (α, β) (wafer scaling): This means that the wafer 8 expands and contracts as a whole due to a processing process or the like. This expansion / contraction amount is represented by wafer scaling Rx and Ry in the α direction and the β direction, respectively. Here, the wafer scaling Rx in the α direction is the ratio between the measured value and the designed value of the distance between the two points in the α direction on the wafer 8, and the wafer scaling Ry in the β direction is the measured value and the designed value between the two points in the β direction. It shall be expressed as a ratio with. Stage coordinate system (X,
Offset for Y): This is caused by the wafer 8 being displaced by a small amount with respect to the wafer stage 10 overall, and is represented by offset amounts O _X and O _Y.

When the error factors (1) to (4) above are added,
Coordinate values on the design of the reference point (C _Xn, C _Yn) for shot area, the stage coordinate system to be positioned when actually exposed (X, Y) on the coordinates _{(C 'Xn, C' Yn} )
Is represented as follows.

[0058]

[Equation 7]

Here, the orthogonality error W and the residual rotation error Θ
When the first-order approximation is performed assuming that is a minute amount, (Equation 7) is as follows.

[0060]

[Equation 8]

Up to this point, accurate alignment of the reference position on each shot area 27-n (in this example, the reference point at the center of each shot area) has been described. However, even if the reference points of the shot areas are accurately aligned, the entire chip pattern in each shot area and the projected image of the reticle do not necessarily exactly overlap each other.

Next, the overlay error in each shot area will be described. As described above, FIG. 6 (b)
In any of the shot area 27-n on the coordinate system (x, y) coordinate values of the design on the _{(S 1Xn, S 1Yn) ~} (S
_4Xn , S _4Yn ) and the alignment marks 2
9-n, 30-n, 34-n, 35-n are formed. In this example, it is assumed that the overlay error in each shot area is caused by the following factors.

Rotation of chip pattern (chip rotation): This is because, for example, when the projection image of the reticle 2 is exposed on the wafer 8, the reticle 2 is rotated with respect to the stage coordinate system (X, Y). Alternatively, it occurs when yawing is mixed in the movement of the wafer stage 10, and the coordinate system (x,
It is represented by the rotation error θ with respect to y). Orthogonality error of chip: This is due to distortion of the pattern itself on the reticle 2 or the distortion (distortion aberration) of the projection optical system 7 when the projection image of the reticle 2 is exposed on the wafer 8. It is an error of orthogonality and is represented by an angular error w.

Linear expansion and contraction of chips (chip scaling): This is an error in the projection magnification when the projection image of the reticle 2 is exposed on the wafer 8, or the wafer 8 is wholly or partially covered by the processing process of the wafer 8. It is caused by stretching. Here, the chip scaling rx in the x direction, which is the ratio between the measured value and the design value of the distance between two points in the x direction of the coordinate system (x, y) of the shot area, and the distance between the two points in the y direction, It is assumed that the y-direction chip scaling ry, which is the ratio between the actually measured value and the design value, represents the linear expansion / contraction in two directions.

For example, FIG. 7A shows a wafer 8A in which a rotation error and a magnification error occur in the chip pattern of each shot area 27-n formed in the previous step.
In (a), an example of a shot area in the case where there is no rotation error and magnification error is a shot area 36-6 surrounded by a broken line.
It is represented by 36-10. On the other hand, the shot areas 27-6 to 27-10 actually formed on the wafer 8A have different rotation angles and magnifications. These errors are
As shown in (b), the chip rotation error in which the shot area 27-n is inclined with respect to the original shot area 36-n, and the magnification of the shot area 27-n as shown in FIG. Can be separated into a chip scaling error different from the original magnification of the shot area 36-n.

However, in the example of FIG. 7, there is no orthogonality error w of the chip pattern, and the chip scaling rx in the x direction.
And the chip scaling ry in the y direction are equal to each other. When the above error factors (1) to (4) are added, the designed coordinate value on the shot area 27-n becomes (S _NXn , S
_NYn ) (N = 1 to 4) alignment marks 29-n, 3
Regarding 0-n, 34-n, 35-n, the coordinate values (S ' _NXn , S' _NYn ) on the coordinate system (x, y) of the shot area to be actually aligned are expressed as follows. It

[0067]

[Equation 9]

Here, if the linear approximation is performed assuming that the orthogonality error w and the rotation error θ are minute amounts, (Equation 9) is expressed by the following equation.

[0069]

[Equation 10]

Now, in FIG. 6B, the array coordinate value of the reference point 28-n of the arbitrary shot area 27-n on the stage coordinate system (X, Y) is (C _Xn , C _Yn ). Therefore, the stage coordinate system (X, X) of the arbitrary alignment mark (29-n or 30-n) on the arbitrary shot area is
The design coordinate values (D _NXn , D _NYn ) on Y) are expressed as follows. However, as described above, the alignment marks 29-n to 35-n are distinguished by the value of N (1 to 4).

[0071]

[Equation 11]

The above three errors (1) to (3) occur when the chip pattern is printed on the layer on which the alignment mark of each shot area on the wafer 8 is printed. In reality, the alignment mark 29 is further affected by the error of the above-mentioned error caused by the processing process of the wafer 8.
-N, 30-n, 34-n, 35-n are the coordinates of the actual position on the stage coordinate system (X, Y) (F _NXn , F
_NYn ) (N = 1 to 4), this coordinate value (F _NXn , F
_NYn ) is expressed from ( _Equation 8) and ( _Equation 10) as follows.

[0073]

[Equation 12]

Next, in the present embodiment, in order to facilitate the application of the method of least squares, the wafer scaling Rx in the α direction and the wafer scaling Ry in the β direction in (Equation 12) are respectively set as new parameters Γx, and It is expressed as in the following (Equation 12) using Γy. Similarly, the chip scaling rx in the x direction and the chip scaling ry in the y direction in the (Equation 12) are expressed as the following (Equation 12) by using new parameters γx and γy, respectively.

[0075]

[Equation 13]

Rewriting (Equation 12) by using the four parameters Γx, Γy, γx, and γy showing the respective changes in the new linear expansion and contraction, (Equation 12) is approximately as follows. Become.

[0077]

[Equation 14]

In this (Equation 14), if the two-dimensional vector is regarded as a matrix of 2 rows × 1 column, this (Equation 14) can be rewritten as a coordinate conversion equation using the following conversion matrix.

[0079]

[Equation 15]

However, each transformation matrix of (Equation 15) is defined as follows.

[0081]

[Equation 16]

The ten error parameters (θ, θ) included in the transformation matrices A, B, O in the coordinate transformation equation of (Equation 15).
W, Γx (= Rx-1 ), Γy, O X, O Y, θ, w, γx
(= Rx−1), γy) can be obtained by, for example, the method of least squares. In this example, the calculated coordinates of each shot area of the wafer 8 on the stage coordinate system (X, Y) and each error of the chip are obtained based on the coordinate conversion formula (Equation 15). Then, based on this, after correcting the chip rotation error, the chip magnification error, etc., each shot area of the wafer 8 is aligned with the reticle.
Note that the least squares method does not necessarily have to be applied to (Equation 15), and for example, 10 error parameters may be obtained at the stage of (Equation 12).

In this example, as described below, the coordinate position of the further selected alignment mark is measured in the shot area (sample shot) selected in advance from the shot area on the wafer, and the measurement result (Number 1
Applying to 5), 10 parameters are obtained by the least squares method, and the array coordinates of each shot area are calculated based on these parameters.

Specifically, in step 105 of FIG. 1, the wafer 8 to be exposed this time is loaded on the wafer holder 9 of FIG. A chip pattern is already formed in each shot area of the wafer 8 in the previous process. Further, as shown in FIG. 6B, four cross-shaped alignment marks 29-n, 30-n, 34- are formed in each shot area 27-n on the wafer 8.
n and 35-n are formed.

Next, in step 106 of FIG. 1, the origin of the wafer 8 is set (pre-alignment). Then, in step 107, the stage coordinates of five or more alignment marks (29-n, 30-n, 34-n or 35-n) on the wafer 8 are aligned using the off-axis alignment system 15 of FIG. The coordinate values (FM _NXn , FM _NYn ) on the system (X, Y) are measured. Since one alignment mark has two components in the X and Y directions, 5
The values of 10 or more parameters can be determined by actually measuring the coordinate values of the or more alignment marks.

The alignment mark actually measured in this example is 3
It is necessary to select one or more shot areas 27-n, but it is not always necessary to select four alignment marks 29-n to 35-n from one shot area 27-n and one shot area 27-n is required. One alignment mark (29-n, 30-n, 34-n or 35-n) may be selected from each of 27-n.

In this case, the reference array points 28-n of the plurality of shot areas 27-n selected on the wafer 8 are arranged on the wafer 8 in the coordinate system (α, β) on the designed array coordinate value (C _Xn ,
C _Yn ) and the designed coordinate values (relative coordinate values) (S _NXn , S _NYn ) in the coordinate system (x, y) on each shot area 27-n of the measured alignment mark are known in advance. There is. Therefore, in step 108, on the right side of (Equation 12), the designed array coordinate values (C _Xn , C _Yn ) of the reference point of the shot area to which the measured alignment mark belongs, and the design regarding the reference point of the alignment mark. By substituting the relative coordinate values (S _NXn , S _NYn ) above, the calculated coordinate values (F _NXn , F _NYn ) that the alignment mark should be on the stage coordinate system (X, Y) are _obtained .

Then, ten error parameters (Θ, W, Γx, Γy, which satisfy (Equation 15) are calculated by the method of least squares.
O _X , O _Y , θ, w, γx, γy) is obtained. In particular,
The difference (E _NXn , E _NYn ) between the actually measured coordinate value (FM _NXn , FM _NYn ) and the calculated coordinate value (F _NXn , F _NYn ) is considered as an alignment error. Therefore, E _NXn = FM _NXn −F
_NXn , E _NYn = FM _NYn- F _NYn holds. Then, five or more sets of alignment errors (E _NXn , E _NYn ), that is, the sum of squares of 10 or more alignment errors are sequentially partial differentiated with these 10 error parameters, and the respective values are 0.
By constructing such an equation and solving the simultaneous equations of ten, ten error parameters can be obtained. This is the EGA calculation of this example.

Then, in step 109, (Equation 5)
With reference to the rotation error Θ _R of the reticle in the conversion matrix AR of, the residual rotation error (wafer rotation error) Θ of the wafer in the conversion matrix A of (Equation 10) and the rotation error θ of the chip rotation in the conversion matrix B. The sum of (θ + θ) is adjusted to the rotation error Θ _R. For that purpose, the wafer 8 is rotated by the wafer stage 10 in FIG. 2, and the traveling direction of the wafer stage 10 is set obliquely in accordance with the rotation of the reticle 2. Instead of rotating the wafer 8,
The reticle 2 side may be rotated.

However, when the wafer 8 is rotated, the offset error (O _X , O _Y ) of the wafer 8 may change. Therefore, after measuring the coordinate value of the alignment mark again, the conventional normal It is necessary to recalculate the error parameter by performing EGA calculation of. Therefore, for example, when the wafer 8 is rotated by a predetermined angle, as in the case where the error in the conventional chip pattern is not considered, the stage coordinate system (X, X, Remeasure the coordinate values in Y). Then, from the result, six error parameters (Θ, W, Rx, Ry,
The values of (O _X , O _Y ) are determined, and each shot area is aligned based on the array coordinates calculated from this result, and exposure is performed. This also means to confirm whether or not the new residual rotation error Θ after the rotation of the wafer 8 is a value corresponding to the angle rotated in step 109.

Next, the orthogonality error W _R of the reticle 2 and the orthogonality error w of the chip cannot be corrected in a strict sense, but the error can be suppressed to a small value by appropriately rotating the reticle 2. Therefore, the orthogonality error W _R of the reticle 2, the rotation error Θ of the wafer 8, the rotation error θ of the chip
It is also possible to optimize the rotation amount of the reticle 2 so that the sum of the absolute values of the square error and the orthogonality error w is minimized.

Next, in step 110, (Equation 5)
Magnification error RRx of the projected image of the reticle 2 in the matrix AR of
The projection magnification of the projection optical system 7 is adjusted via the imaging characteristic control device 14 of FIG. 2 so as to correct the RRy and the chip scaling errors rx and ry in the conversion matrix B of (Equation 10). In this case, in this embodiment, since the magnification of the projected image of the reticle 2 can be directly measured, the magnification errors RRx and RRy of the reticle 2 are exactly 1 when the first layer on the wafer 8 is exposed. The projection magnification of the projection optical system PL is adjusted so that Magnification errors RRx and RRy are exactly 1
The projection optical system PL for the pattern of the reticle 2
The projected image by is the size as designed.

As shown in FIG. 5, the alignment mark images 43AW to 43HW of the reticle 2 of this embodiment may be outside the actual rectangular exposure area within the effective exposure field 42 of the projection optical system PL. Therefore, the projection optical system P
When measuring the projection magnification of L, it is greatly affected by lens distortion. Therefore, by using a reference reticle in which an alignment mark image is projected in the exposure area in advance, offset correction of the projection magnification of the projection optical system PL is performed so that the magnification of the projection image of the reference reticle is equal to the design value. You may go. In this case, it is not necessary to correct the projection magnification when exposing the first layer on the wafer 8.

Next, when the pattern image of the reticle 2 is exposed on the second and subsequent layers of the wafer 8, the projection magnification of the projection optical system PL is corrected with reference to the chip scaling errors rx and ry. As a result, the size of the projected image of the reticle 2 becomes equal to the size of the chip pattern already formed on the wafer 2. Then, step 111 of FIG.
In the following, using the conversion matrices A and O including the elements composed of the error parameters obtained in step 108, the design array coordinate value (of the reference point 28-n of each shot area 27-n on the wafer 8 is designed as follows: By substituting C _Xn , C _Yn ), a calculated array coordinate value (G _Xn , G _Yn ) of the reference point 28-n on the stage coordinate system (X, Y) is obtained. However, as described above, when the wafer 8 side is rotated to correct the rotation error in step 105,
Based on the measured coordinates of the alignment mark again, the calculated array coordinate value (G _Xn , G _Yn ) of each reference point 28-n on the stage coordinate system (X, Y) is obtained.

[0095]

[Equation 17]

Then, in step 112, the reference point 28- of each shot area 27-n on the wafer 8 is based on the array coordinates (G _Xn , G _Yn ) obtained by the calculation and the previously determined baseline amount. n is sequentially aligned with a predetermined position in the exposure field of the projection optical system PL of FIG. 2, and the pattern image of the reticle 2 is projected and exposed on the shot area 27-n. Then, after the exposure of all shot areas on the wafer 8 is completed, processing such as development of the wafer 8 is performed.

In this case, in this example, (Equation 5) and (Equation 1)
As shown in 5), since not only the transformation matrices A and O but also reticle rotation error, reticle magnification error, chip rotation, chip scaling parameters, etc. are taken into consideration, rotation of the reticle 2 and projection optics are performed. The influence of the magnification error of the system PL, the expansion and contraction and rotation of the chip pattern itself transferred to each shot area is suppressed to a small level, and the chip pattern of each shot area on the wafer and the projected image of the reticle pattern are superimposed with high accuracy. Can be matched.

In the above-described embodiment, as shown in FIG. 6B, a cross-shaped alignment mark 29-n that can be simultaneously aligned in the X and Y directions on the stage coordinate system.
2 to 35-n on the x-axis on the coordinate system of the shot area,
And two on the y-axis. However, for example, 1
If the four alignment marks are not arranged on a straight line, such an arrangement is not always necessary. As an example, alignment marks may be arranged at the four corners of each shot area. Further, each alignment mark may be formed on the street line area between each shot area. Further, even if the one-dimensional alignment mark for the X direction and the one-dimensional alignment mark for the Y direction are separately provided, the conversion matrix A of (Equation 15) is exactly the same as in the above embodiment if the arrangement is taken into consideration. , B, O can be obtained.

However, in the case of using a one-dimensional alignment mark (diffraction grating mark or the like) that can detect only the position in the X direction or the Y direction, instead of the cross mark that can specify the two-dimensional position as in this example. Must measure the coordinate values of 10 or more one-dimensional alignment marks in order to determine the values of 10 parameters. In the above embodiment, in order to obtain the rotation error θ of the chip rotation, the orthogonality error w of the chips, and the chip scaling rx and ry, 4 shots are formed in each shot area 27-n of the wafer 8.
Two two-dimensional alignment marks 29-n to 35-n are provided. However, even if the offset (x direction and y direction) of the reference point of each shot area 27-n is taken into consideration, there are six parameters to be obtained, so each shot area 27-n has three two-dimensional parameters. Alignment marks (for example, 29-n, 30-n and 34-n) may be simply provided. Thus, when using the two-dimensional alignment mark, two alignment marks are always selected. However, if it is a one-dimensional alignment mark, it is necessary to form six alignment marks in each shot area 27-n.

In the above embodiment, multipoint measurement is performed within each shot area on the wafer 8.
The method may be applied as it is to detect the position of one specific mark in each shot area. In this case, the matrix B in (Equation 15) may be ignored, and the wafer rotation error Θ may be matched with the reticle rotation error Θ _R , for example.

In the above embodiment, the orthogonality error W _R of the reticle 2 is not positively corrected. However, for example, a part of the lenses forming the projection optical system PL is formed on the toroidal surface, and a mechanism for rotating the lenses around the optical axis is provided. With this mechanism, the orthogonality error W _R of the projected image is minimized. The lens may be rotated so that As a result, the orthogonality error W _R due to the drawing error of the reticle 2 and the like can be reduced.

The alignment method in which the shot arrangement error in the wafer is linear as in the above embodiment belongs to the EGA method. Further, in the EGA method of the above-described embodiment, the error in the chip rotation and the chip magnification (including distortion) for each shot area is constant within the same wafer, and the chip rotation and the chip magnification error are obtained. For this reason,
If the local array error on the wafer or the fluctuation (non-linearity) of the distortion component is large, it becomes difficult to improve the overlay accuracy in the above-described embodiment. Therefore, even with a wafer having non-linear distortion, there is a demand for an alignment method that can satisfactorily correct the chip rotation and the chip magnification error and perform highly accurate alignment. In the following, an embodiment will be described in which the above-mentioned EGA method is improved to perform positioning with higher accuracy. As this alignment method, the alignment method proposed in Japanese Patent Application No. 4-297121 is applied to the above embodiment.

FIG. 8 for such another embodiment of the present invention.
Will be described with reference to. The projection exposure apparatus shown in FIG. 2 is also used in this example, but in this example, the EGA used in the first example is used.
The first weighted enhanced global alignment method (hereinafter,
"W1-EGA method") is performed.
This W1-EGA method alignment is effective against “regular non-linear distortion”, and “even if the substrate has a regular non-linear distortion, the alignment error in the local region on the substrate is small. It is focused on "almost equal". Then, in this W1-EGA alignment, weighting is performed according to the distance to the sample shot, as described later.

FIG. 8 shows a wafer 8 to be exposed in this example. In FIG. 8, when the calculated coordinate position of the i-th shot area ESi on the wafer 8 is determined, the shot areas ESi and m According to the distances LK1 to LK9 between the individual sample shots SA1 to SA9 (m = 9 in FIG. 8), the measured coordinate positions (alignment data) of the alignment marks in these nine sample shots are set. A weight W _in is given. Specifically, the two alignment marks MA1 and MB of the sample shot SA1
A weight W _i1 corresponding to the distance LK1 is given to the measured coordinate position of ₁ . More strictly, it is desirable to give weights according to the distance from the reference point of the shot area ESi to each alignment mark in each sample shot. Further, it is not always necessary to measure the coordinates of the two alignment marks in each sample shot.

In this W1-EGA system, the EGA system is used.
Instead of just the residual error component of the sum of squares in
The residual error component Ei defined by (Equation 13) is defined. this
In (Equation 18), the coordinate value (FM_NXn , FM_NYn )
Is the Nth alignment in the nth sample shot
Coordinate values actually measured, and coordinate values (F_NXn ，
F _NYn ) Is the calculated coordinate value.

[0106]

[Equation 18]

Then, ten error parameters (Θ, W, Γx, Γy, O _X , O _Y , θ, which satisfy (Equation 15) so that the residual error component Ei defined in this way is minimized.
w, γx, γy) is obtained. Note that here, sample shots SA1 to SA used for each shot area ESi
9 is the same, but naturally the distance to each sample shot SAn is different for each shot area ESi. Therefore,
The weight W _in given to the coordinate position (alignment data) of the sample shot SAn changes for each shot area ESi. Then, error parameters (Θ, W, Rx, Ry, O _X , O _Y , θ, w, rx, ry) for each shot area ESi.
And first, the wafer rotation error Θ in the conversion matrix A of (Equation 15) and the chip rotation error θ in the conversion matrix B are corrected, and the chip magnification error ((15) in the conversion matrix B of (Equation 15) is determined. Chip scaling γx, γ
Correct y).

After that, the error parameters (Θ, W, Γx,
By using the conversion matrices A and O including the elements composed of Γ y, O _X , O _Y ), the shot area E on the wafer 8 is expressed by
By substituting the design coordinate values of Si, the stage coordinate system (X,
Y) Calculate the calculated array coordinate value. As already described, when the wafer side is rotated, the array coordinate value is obtained by the normal EGA calculation based on the coordinates of the alignment mark newly measured.

Thus, in the W1-EGA method, the wafer 8 is
For each shot area ESi above, each sample shot S
The weight W _in of the coordinate data of An changes. As an example, the weight W _{in is set} to the i-th shot area ESi and n.
It is expressed as follows as a function of the distance LKn from the th sample shot SAn. However, the parameter S is a parameter for changing the degree of weighting.

[0110]

[Formula 19]

As is clear from this (Equation 19), the i-th
Sample with short distance LKn to shot area ESi
Shot SAn gives more weight to the alignment data
Only W _inIs becoming larger. Also, (Equation 1
In 9), if the value of the parameter S is sufficiently large,
The result of the total calculation processing is obtained by the EGA method of the above-mentioned embodiment.
It is almost equal to the result. On the other hand, the wafer to be exposed on the wafer
All the shot areas ESi are sample shots SAn,
If the value of the parameter S is close to zero, each shot area
Position the wafer mark by measuring the position of the wafer mark for each area
Almost equal to the result obtained by the so-called die-by-die method
Become. That is, in the W1-EGA method, the parameter S is
By setting the appropriate value, EGA method and die-by
-It is possible to obtain an effect intermediate to that of the die method. example
For example, for wafers with large nonlinear components, the parameters
By setting the value of S small, the die-by-die method
It is possible to obtain the same effect (alignment accuracy) as
Satisfactorily removes alignment errors due to nonlinear components.
You can In addition, the alignment sensor measurement
If the actuality is poor, increase the value of parameter S.
By doing so, it is possible to obtain almost the same effect as the EGA method.
And reduce alignment error by averaging effect
You can

Further, the weighting function of (Equation 19) is separately prepared for the X coordinate and the Y coordinate of the alignment mark so that the weight W _in can be set independently for the X coordinate and the Y coordinate. Good. In this case, the degree of nonlinear distortion of the wafer (magnitude), regularity or step pitch,
That is, even if the center-to-center distance between two adjacent shot areas (which depends on the width of the street line on the wafer but is a value substantially corresponding to the shot size) is different in the X and Y directions, the value of the parameter S is By setting them independently, the shot arrangement error on the wafer can be corrected with high accuracy. At this time, the value of the parameter S may be different between the X coordinate and the Y coordinate as described above.
Further, whether the value of the parameter S of the X coordinate and the value of the Y coordinate are the same or different, the value of the parameter S is the magnitude of the "regular non-linear distortion", the regularity, the step pitch, or the measurement reproduction of the alignment sensor. It may be appropriately changed according to the nature.

From the above, the effect can be changed from the EGA method to the die-by-die method by appropriately changing the value of the parameter S. Therefore, for each layer, and for each component (X direction and Y direction), alignment is performed according to, for example, the characteristics of the non-linear component (for example, size, regularity, etc.), the step pitch, and the quality of the measurement repeatability of the alignment sensor. It is possible to flexibly change and perform alignment under optimum conditions for each layer and each component.

Next, referring to FIG. 9, a second weighted enhanced global alignment method (hereinafter, referred to as
An alignment method of "W2-EGA method") will be described. Here, in order to simplify the explanation, the wafer W
In particular, it is assumed that the point-symmetrical non-linear distortion occurs regularly, and that the point-symmetrical center coincides with the center of the wafer W (wafer center).

FIG. 9 shows a wafer 8 to be exposed in the present example. In FIG. 9, the deformation center point of the wafer 8 (center of point symmetry of nonlinear distortion), that is, the wafer center Wc and the i-th wafer on the wafer 8 are shown. The distance (radius) from the shot area ESi to the wafer center Wc is m (see FIG. 1).
1, the distance (radius) between each of the sample shots SA1 to SA9 of m = 9) is LW1 to LW9.
Also in this W2-EGA method, as in the W1-EGA method, the measured coordinate positions (alignment data) of the alignment marks in the nine sample shots SA1 to SA9 according to the distance LEi and the distances LW1 to LW9. Give each of the weights W _in ′. In this W2-EGA method, after detecting two alignment marks (MAi, MBi) for each sample shot, the residual error component Ei 'is defined by the following (Equation 20) as in (Equation 18). The error parameters (Θ, W, Γx, Γy, O _X , O _Y , θ, w, γx, of (Equation 15) are minimized so that (Equation 20) is minimized.
γy) is determined.

[0116]

[Equation 20]

In the W2-EGA method as well, as in the W1-EGA method, the weight W _in ′ given to the alignment data changes for each shot area ESi.
A statistical calculation is performed for each Si to obtain error parameters (Θ, W, Γ
x, Γy, O _X , O _Y , θ, w, γx, γy),
The chip rotation, the chip orthogonality, the chip magnification error, and the calculated array coordinate value will be determined.

Then, each shot area ES on the wafer W is
for each i, 'to change the weights W _in the equation (20)' weight W _in for each sample shots, i th shot area ESi and the wafer center W on the wafer 8
It is expressed as a function of the distance (radius) LEi from c as follows. However, the parameter S is a parameter for changing the degree of weighting.

[0119]

[Equation 21]

As is apparent from this (Equation 21), the sample shot SAn has a distance LWn to the wafer center Wc close to the distance LEi between the wafer center Wc and the i-th shot area ESi on the wafer W. The more the weight W _in ′ given to the alignment data increases. In other words, the largest weight W _in ′ is given to the alignment data of the sample shot located on the circle having the radius LEi centered on the wafer enter Wc, and the weight W to the alignment data is increased as the distance from the circle in the radial direction increases. _in ′
Is getting smaller.

The value of the parameter S in (Equation 21) is the same as that required in the W1-EGA method, such as alignment accuracy, nonlinear distortion characteristics (for example, size, regularity, etc.),
It may be appropriately determined depending on the step pitch, the quality of measurement reproducibility of the alignment sensor, and the like. That is, when the non-linear component is relatively large, the value of the parameter S is set to be smaller so that the distance LWn from the wafer center Wc is reduced.
It is possible to reduce the influence of the sample shots that greatly differ from each other. On the other hand, when the non-linear component is relatively small, by setting the value of the parameter S larger, it is possible to prevent the alignment accuracy of the alignment sensor (or layer) having poor measurement reproducibility from being degraded.

Further, in the W2-EGA method, a plurality of shot areas located substantially equidistant from the point symmetry center on the wafer W, that is, a plurality of shot areas located on the same circle centered on the point symmetry center are used. In each case, naturally, the weight W _in ′ given to the alignment data of the sample shot is the same. Therefore, when a plurality of shot areas are located on the same circle centered on the point symmetry center, the weighting and the statistical calculation are performed only on any one of the shot areas to perform the error parameter (Θ, W , Γx, Γ
y, O _X , O _Y , θ, w, γx, γy), the chip rotation, the chip orthogonality, the chip magnification error, and the coordinates of the remaining shot area are directly used for the remaining shot areas. The position can be determined. This has the advantage of reducing the amount of calculation.

By the way, it is desirable to specify the sample shot arrangement suitable for the W2-EGA method so as to be symmetric with respect to the point symmetry center of the non-linear distortion, that is, the wafer center Wc. For example, X with reference to the wafer center Wc. It may be specified as a character shape or a cross shape. Besides that,
The arrangement may be similar to that of the W1-EGA method. If the point-symmetric center of the non-linear distortion is other than the wafer center Wc, the X-shaped or cross-shaped arrangement may be used with the point-symmetric center as a reference. When determining the value of the error parameter, the weighting function shown in (Equation 21) may be set independently in each of the X direction and the Y direction.
Needless to say, the weighting function may be set independently for each alignment mark.

The W1-EGA method and the W2-EGA method
In the method, when correcting the rotation error and the magnification error based on the four error parameters (θ, w, rx, ry) related to the chip pattern, the parameters obtained for each shot region are used for each shot region. Correction may be performed. Alternatively, one set of parameters obtained for each shot area may be averaged to obtain one set of parameters, and based on this parameter, the entire wafer may be corrected only once. Further, the wafer may be divided into a plurality of blocks and the correction may be performed for each block. Further, in the W2-EGA method, it is not necessary to obtain a parameter for each shot region in a shot region located concentrically with respect to the center of point symmetry, and the parameter obtained for any one shot region is used. May be.

In the embodiment described above, when the correction of the reticle rotation or the correction of the projection magnification of the projected image of the reticle (correction in the exposure of the second and subsequent layers) is performed, the rotation and expansion / contraction of the wafer and the chip pattern side are performed. I am also considering. However, for example, when it is known that the magnification error and the rotation error of the wafer and the chip pattern are sufficiently small due to the exposure up to that time in the same lot, the measurement based on (Equation 5) of the reticle (EGA measurement). The rotation correction of the reticle or the projection magnification of the projection optical system may be performed using only the result of the above.

The present invention is not limited to the step-and-repeat type exposure apparatus (for example, the reduction projection type stepper or the unit-magnification projection type stepper), but also a so-called step-and-scan exposure type exposure apparatus or proxy. The present invention can be widely applied to a mitty type stepper (X-ray exposure device, etc.). In addition to the exposure equipment, it is an equipment (defect inspection equipment, prober, etc.) that inspects semiconductor wafers and reticles with multiple chip patterns, and uses a step-and-repeat method for each chip as a standard for inspection fields and probe needles. The present invention can be similarly applied to a device for aligning with respect to a position.

When the above-described alignment method is applied to a scanning type exposure apparatus such as a step-and-scan exposure type exposure apparatus, a predetermined offset ( The scanning exposure is performed after the wafer is positioned at a position to which a value that is uniquely determined according to the pattern size, the reticle, the run-up section of the wafer, etc. is added.

As described above, the present invention is not limited to the above-described embodiments, and various configurations can be taken without departing from the gist of the present invention.

[0129]

According to the present invention, since the position of the image of the mark for position detection on the mask through the projection optical system is measured and the measurement result is statistically processed, the rotation angle of the mask pattern is changed. Alternatively, the orthogonality of the pattern can be accurately obtained. Further, there is an advantage that the magnification of the projected image through the projection optical system can be accurately obtained and the overlay accuracy of the pattern on the mask and the pattern on the substrate can be improved.

Further, when the array coordinates on the substrate side are obtained by the EGA method, the alignment accuracy and the overlay accuracy can be further improved.

[Brief description of drawings]

FIG. 1 is a flowchart showing an embodiment of an exposure method according to the present invention.

FIG. 2 is a configuration diagram showing an example of a projection exposure apparatus in which the exposure method of the embodiment is implemented.

FIG. 3 is an enlarged view showing an image of an alignment mark on the index plate of FIG.

4A is a plan view showing a pattern arrangement of a reticle 2 used in the embodiment, and FIG. 4B is an enlarged plan view showing a configuration of an alignment mark on the reticle 2.

5 is a plan view showing a projected image of the reticle 2 of FIG. 4 (a).

6A is a plan view showing an example of an arrangement of shot areas on a wafer according to an embodiment, and FIG. 6B is an enlarged plan view showing the shot areas in FIG. 4A.

FIG. 7A is a plan view showing an example of a wafer including a rotation error of a chip pattern and an error of a chip magnification, and FIG.
FIG. 6 is an explanatory diagram of a chip rotation error, and FIG. 7C is an explanatory diagram of a chip magnification error.

FIG. 8 is a plan view showing a shot array on a wafer on which W1-EGA alignment is performed in another embodiment of the present invention.

FIG. 9 is a plan view showing a shot array on a wafer on which W2-EGA alignment is performed in another embodiment of the present invention.

[Explanation of symbols]

1 Illumination Optical System 2 Reticle 6 Main Control System PL Projection Optical System 7 Photoelectric Sensor 8 Wafer 10 Wafer Stage 12 Laser Interferometer 14 Imaging Characteristic Control Device 15 Off-Axis Alignment System 27-1 to 27-5, 27- n shot areas 28-1 to 28-5, 28-n reference points 29-1 to 29-3, 29-n alignment marks 43A to 43E on wafer alignment marks on reticle

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-3-96219 (JP, A) JP-A-2-27712 (JP, A) JP-A-2-81419 (JP, A) JP-A-2- 148714 (JP, A) JP-A 64-53545 (JP, A) JP-A 6-349705 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 21/027 G03F 9 / 00

Claims (25)

(57) [Claims] 1. An exposure method of illuminating a mask on which an exposure pattern is formed and projecting and exposing the pattern of the mask onto a photosensitive substrate positioned on a first coordinate system via a projection optical system. In the above, a mask for actual exposure in which a plurality of marks for position detection is formed together with an exposure pattern on the mask is used as the mask, and positioning is performed on the second coordinate system on the mask for actual exposure. A first step of detecting the position of the image of the detected position detection mark on the first coordinate system through the projection optical system, and the position detection mark detected in the first step A statistical conversion of the position of the image of the image is obtained to obtain a conversion parameter from the coordinate on the second coordinate system on the mask for actual exposure to the coordinate on the first coordinate system on which the substrate is positioned. Two steps, and the second step Based on the conversion parameter obtained in the step, after adjusting the imaging state of the projection optical system and positioning the mask for the actual exposure and the substrate, the exposure mask for the actual exposure is exposed. An exposure method comprising exposing a pattern onto the substrate. 2. The plurality of processed regions arranged on the substrate based on the arrangement coordinates on the third coordinate system set on the substrate, and at least three preselected sample regions Coordinates on the first coordinate system are calculated from coordinates on the third coordinate system on the substrate by measuring coordinate positions on the first coordinate system and statistically calculating the plurality of measured coordinate positions. To the first coordinate system from the third coordinate system, and based on the conversion parameter obtained in the second step, the image forming state of the projection optical system is calculated. After adjusting and positioning the actual exposure mask and the substrate,
The exposure method according to claim 1, wherein the exposure pattern of the mask for actual exposure is exposed on the substrate. 3. An exposure method of illuminating a mask on which an exposure pattern is formed and projecting and exposing the pattern of the mask onto a substrate through a projection optical system, wherein the mask is used together with the exposure pattern on the mask. A mask for actual exposure on which a plurality of position detection marks are formed is used, and a pattern of the mask for actual exposure is used.
Before exposure on the substrate, a pattern is formed on the mask for actual exposure.
A first step of detecting position information about the plurality of position detection marks formed, and a step of obtaining a plurality of error parameters by performing statistical calculation using the position information detected in the first step. Two steps, and a third step of controlling the imaging characteristic of the projection optical system based on the error parameter obtained in the second step,
An exposure method comprising: 4. The exposure method according to claim 3, wherein the error parameter includes a magnification error in a coordinate system on the mask. 5. The exposure method according to claim 4, wherein in the third step, the projection magnification of the projection optical system is controlled based on the magnification error. 6. The projection optical system is composed of a plurality of lens groups, and in the third step, an interval between predetermined lens groups of the lens groups forming the projection optical system is adjusted, or The exposure method according to claim 5, wherein the pressure of the gas in the lens chamber between the predetermined lens groups is adjusted. 7. The magnification error is a value of a ratio between an actual measurement value and a design value, and when the pattern image of the mask is exposed on the first layer on the substrate, the magnification error becomes 1. 7. The exposure method according to claim 4, wherein the projection magnification of the projection optical system is adjusted as described above. 8. When the pattern image of the mask is exposed on the second and subsequent layers on the substrate, the projection is performed so that the magnification error matches the magnification error of a pattern already formed on the layer. 7. The exposure method according to claim 4, 5 or 6, wherein the projection magnification of the optical system is adjusted. 9. An exposure method of illuminating a mask on which an exposure pattern is formed and projecting and exposing the pattern of the mask onto a substrate through a projection optical system, wherein the mask is used together with the exposure pattern on the mask. A mask for actual exposure on which a plurality of position detection marks are formed is used, and a pattern of the mask for actual exposure is used.
Before exposure on the substrate, a pattern is formed on the mask for actual exposure.
Performing statistical calculation using the plurality of position detection marks which are made, a first step of detecting the positional information of the image through the projection optical system, the position information detected by the first step And a second step of obtaining a plurality of error parameters. 10. The projection image of the position detection mark is detected in the first step based on an output of a photoelectric detector provided on a stage on which the substrate is placed. The exposure method according to 1 or 9. 11. The error parameter includes error information of a second coordinate system on the mask with respect to a first coordinate system that defines the position of the substrate. The exposure method described in. 12. The plurality of parameters include a rotation error of the mask, an orthogonality error of the second coordinate system, and the second error.
Magnification error of the mask in the coordinate system of
At least one of the offset errors of the second coordinate system with respect to the second coordinate system.
Or the exposure method according to item 11. 13. The exposure method according to claim 12, wherein the mask or the substrate is rotated based on a rotation error of the mask. 14. The exposure method according to claim 12, wherein the projection optical system includes a predetermined lens formed on a toroidal surface, and the predetermined lens is rotated based on the orthogonality error. 15. The exposure method according to claim 1, wherein the statistical calculation includes a least squares method. 16. The pattern image and the substrate are moved relative to each other while the pattern image on the mask is projected on the substrate. The exposure method described in. 17. A method of exposing a circuit pattern for forming a semiconductor element or a liquid crystal display element onto a substrate by using the exposure method according to claim 1. Element manufacturing method. 18. An exposure apparatus for illuminating a mask on which an exposure pattern is formed and projecting and exposing the pattern of the mask onto a substrate through a projection optical system, wherein the mask is for exposure on the mask. A mask for actual exposure in which a plurality of position detection marks are formed together with a pattern is used, and a pattern of the mask for actual exposure is used.
Before exposure on the substrate, a pattern is formed on the mask for actual exposure.
A detection unit that detects position information regarding the plurality of position detection marks that are formed; and a calculation unit that calculates a plurality of error parameters by performing statistical calculation using the position information detected by the detection unit. A control means for controlling the imaging characteristic of the projection optical system based on the error parameter obtained by the calculation means,
An exposure apparatus comprising: 19. The error parameter includes a magnification error in a coordinate system on the mask, and the control unit controls a projection magnification of the projection optical system based on the magnification error. Item 18
The exposure apparatus according to. 20. The projection optical system is composed of a plurality of lens groups, and the control means adjusts an interval between predetermined lens groups of the lens groups forming the projection optical system, or 20. The exposure apparatus according to claim 19, wherein the pressure of the gas in the lens chamber between the lens groups is adjusted. 21. An exposure apparatus for illuminating a mask on which an exposure pattern is formed and projecting and exposing the pattern of the mask onto a substrate via a projection optical system, wherein the mask is used for exposure on the mask. A mask for actual exposure in which a plurality of position detection marks are formed together with a pattern is used, and a pattern of the mask for actual exposure is used.
Before exposure on the substrate, a pattern is formed on the mask for actual exposure.
Of said plurality of position detection marks which are made, a detecting means for detecting the position information of the image through the projection optical system, by performing the statistical calculation using the position information detected by said detecting means And an arithmetic unit that obtains a plurality of error parameters. 22. The exposure apparatus according to claim 21, wherein the detection unit includes a photoelectric detector provided on a stage on which the substrate is placed. 23. The error parameter includes a rotation error of the mask, and the mask or the substrate is rotated based on the rotation error of the mask. The exposure apparatus according to the item. 24. The plurality of error parameters include an orthogonality error of a coordinate system on the mask, the projection optical system includes a predetermined lens formed on a toroidal surface, and the projection optical system includes the orthogonality error based on the orthogonality error. The exposure apparatus according to any one of claims 18 to 23, comprising a mechanism for rotating a predetermined lens. 25. The pattern image and the substrate are moved relative to each other while the pattern image on the mask is projected on the substrate. The exposure apparatus according to.