JP4314867B2 - Manufacturing method of MEMS element - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a MEMS device .
[0002]
[Prior art]
With the progress of micro technology, so-called micromachine (MEMS: Micro Electro Mechanical Systems) devices and small devices incorporating MEMS devices are attracting attention.
A MEMS element is formed as a fine structure on a substrate such as a silicon substrate or a glass substrate, and electrically and mechanically connects a driver that outputs a mechanical driving force and a semiconductor integrated circuit that controls the driver. It is an element coupled to. A basic feature of the MEMS element is that a drive body configured as a mechanical structure is incorporated in a part of the element. The drive of the drive body is an electrostatic force between electrodes, that is, a clone attractive force, etc. Is applied electrically.
[0003]
On the other hand, a microresonator in which a vibrating electrode is arranged with a nanometer-level hollow gap as a MEMS element has a wide application field such as a MEMS filter and a sensor detection circuit because of its high electric / mechanical conversion efficiency. . For example, use as a high-frequency filter has been proposed by research institutions such as the University of Michigan (see Non-Patent Document 1).
[0004]
FIG. 4B shows an outline of a MEMS element applied to the MEMS vibrator constituting the high frequency filter described in Non-Patent Document 1. The MEMS element 1 has a fixed-side electrode 6 and a wiring layer 7 on both sides thereof formed on an insulating film 3 on a semiconductor substrate 2, and can be driven with a hollow gap 9 facing the first electrode 6. A so-called drive side electrode 8 is formed. The drive side electrode 8 is connected to the wiring layer 7 across the fixed side electrode 6 in a bridge shape so as to be supported by the anchor portions (support portions) 14 [14A, 14B] at both ends. As the insulating film 3 on the semiconductor substrate, for example, a two-layer film of a silicon oxide film 4 and a silicon nitride film 5 is used. When the MEMS element 1 is applied as a MEMS vibrator, the fixed electrode 6 serves as an input electrode, and the drive electrode 8 serves as an output electrode.
[0005]
In the manufacturing process of the MEMS element 1, in the step of forming the hollow gap 9, as shown in FIG. A connection hole (contact hole) 11 reaching the wiring layer 7 is formed in the layer 10, and a desired vibration electrode 8 is formed so as to sandwich the sacrificial layer 10. Next, as shown in FIG. 5B, the sacrificial layer 10 is removed with a chemical solution or the like to form the gap 9. That is, since the thin film sacrificial layer 10 and the LSI are mixedly mounted, in order to realize the merit of using the same manufacturing process, the fixed side electrode (output) electrode 6, the wiring layer 7 and the vibration electrode 8 are made of polysilicon, and the sacrificial layer 10 is made. An oxide film (SiO ₂ ) is used. In order to perform the thinning 10 of the sacrificial layer with high control, a method in which the sacrificial layer 10 is removed by forming a structure in which the driving side electrodes 8 facing each other are stacked in the vertical direction is generally used.
[0006]
[Non-Patent Document 1]
C. T.A. -Nguyen, "Micromechanical components for miniaturized low-power communications (invited plenary)," proceedings, 1999 IEEE MTT-S International Microswing. 48-77.
[0007]
[Problems to be solved by the invention]
By the way, when the sacrificial layer 10 is thinned, a problem as shown in the manufacturing process of FIG. 5 occurs. In this manufacturing process, first, as shown in FIG. 5A, after a silicon oxide film (SiO ₂ ) 4 is formed on a silicon substrate 2 and a silicon nitride film (SiN) 5 is formed, a fixed side made of a polysilicon film is formed. The electrode 6 and the wiring layer 7 are formed.
[0008]
Next, as shown in FIG. 4B, a sacrificial layer 10 made of a silicon oxide film (SiO ₂ ) is formed on the substrate including the fixed side electrode 6 and the wiring layer 7.
Next, as shown in FIG. 4C, a connection hole 11 is formed so as to reach the wiring layer 7 in a part of the sacrifice layer 10.
[0009]
Next, in order to improve the contact between the driving side electrode 8 and the wiring layer 7 later, a natural oxide film on the surface of the wiring layer 7 in the connection hole 11 is cleaned with a hydrofluoric acid (HF) solution. Cleaning is performed. However, when immersed in a hydrofluoric acid solution for the purpose of this contact cleaning, the sacrificial layer 10 is etched as shown in FIG. 5D. However, if the sacrificial layer 10 is thick, it can be dealt with by precisely controlling the contact cleaning time. However, the sacrificial layer 10 has been thinned to the level of several nanometers of the film to be cleaned (so-called natural oxide film). In some cases, the control itself is difficult.
[0010]
In view of the above-mentioned points, the present invention provides a method for manufacturing a MEMS element in which the gap between the hollow gaps is made ultrafine to the nanometer level.
[0011]
[Means for Solving the Problems]
A method for manufacturing a MEMS device according to the present invention includes a step of forming a first electrode and a wiring layer having removal selectivity with respect to a sacrificial layer on a substrate, and a sacrifice on the substrate including the first electrode and the wiring layer. Forming a layer, forming a first conductor thin film on the sacrificial layer, forming a connection hole reaching the wiring layer in the first conductor thin film and the sacrificial layer, and removing the sacrificial layer in the connection hole A step of cleaning with an etchant, a step of forming a second conductive thin film on the first conductive thin film so as to be electrically connected to the wiring layer through a connection hole, and patterning the first and second conductive thin films Then, there is a step of forming a second drivable electrode made of the first and second conductive thin films and a step of removing the sacrificial layer.
[0012]
In the method for manufacturing a MEMS element according to the present invention, after forming the sacrificial layer, a first conductor thin film serving as a second electrode is formed on the sacrificial layer, and the sacrificial layer and the first conductor thin film are formed on the wiring layer. Since the connecting hole reaching step is formed, the sacrificial layer is not removed during the subsequent cleaning in the connecting hole. In particular, even when the sacrificial layer is formed with a thickness of nanometer level, the sacrificial layer is protected by the first conductive thin film, and the sacrificial layer is not lost by washing in the connection hole. Therefore, by removing the sacrificial layer thereafter, a gap (hollow gap) having a nanometer level gap is formed between the first electrode and the second electrode.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0014]
FIG. 1 shows an example of a MEMS element obtained by the method for manufacturing a MEMS element according to the present invention.
The MEMS element 21 according to this example includes first electrodes (hereinafter referred to as fixed-side electrodes) arranged on the same plane of the substrate 20, that is, on the surface having at least an insulating property of the substrate 12 with a predetermined interval therebetween. ) 26 and wiring layers 27 located on both sides of the fixed side electrode 26 are formed, and first and second conductive thin films constituting a two-layer film that can be driven with the gap 31 interposed between the fixed side electrode 26 A second electrode (so-called beam, hereinafter referred to as drive side electrode) 28 comprising 29 and 30 is arranged. The drive side electrode 28 straddles the fixed side electrode 26 in a bridge shape, and is supported integrally by connecting both ends thereof, in particular, the second conductive thin film 30 to the wiring layer 27. In the connection portion between the second conductor thin film 30 and the wiring layer 27, a part of the second conductor thin film 30 is formed so as to enter the gap 31 side.
[0015]
As the substrate 20, for example, a substrate in which an insulating film is formed on a semiconductor substrate such as silicon (Si) or gallium arsenide (GaAs), an insulating substrate such as a quartz substrate or a glass substrate, or the like is used. In this example, a substrate 20 in which a laminated insulating film 23 of a silicon oxide film (SiO ₂ ) 24 and a silicon nitride film (SiN) 25 is formed on a silicon substrate 22 is used. The fixed side electrode 26 and the wiring layer 27 are formed of the same conductive material, for example, a polysilicon film or a metal film such as aluminum (Al), tungsten (W), chromium (Cr), nickel (Ni). be able to. The drive-side electrode 28 can also be formed of, for example, a polysilicon film or a metal film such as aluminum (Al), tungsten (W), chromium (Cr), nickel (Ni).
In this example, the first conductor thin film 29 and the second conductor thin film 30 constituting the fixed side electrode 26, the wiring layer 27, and the drive side electrode 28 are all formed of a polysilicon film. In addition, the first conductor thin film 29 and the second conductor thin film 30 constituting the fixed side electrode 26, the wiring layer 27, and the driving side electrode 28 can be formed of the different material films, respectively. Alternatively, any one of the first conductor thin film 29 and the second conductor thin film 30 constituting the fixed side electrode 26, the wiring layer 27, and the drive side electrode 28 and another layer may be made of the above different material films. It is also possible to form.
[0016]
According to the MEMS element 21 according to this example , the drive-side electrode 28 is formed by a two-layer film including the first conductor thin film 28 and the second conductor thin film 30, and the second conductor thin film 30 is formed as the first layer. In this configuration, the wiring layer 27 is connected through a connection hole formed in the conductor thin film 29. Thus, when the connection hole is formed 4 in the sacrificial layer in the region that becomes the gap 31 in the manufacturing process, the connection hole can be formed together with the sacrificial layer and the first conductor thin film 29 of the driving side electrode 28 thereon. Then, the sacrificial layer can be prevented from disappearing when the inside of the connection hole is washed, and the gap 31 between the fixed-side electrode 26 and the drive-side electrode 28 is formed with a nanometer (nm) level gap. It becomes possible to form. That is, the MEMS element 21 of this example can provide a MEMS element with a finer structure and higher accuracy.
[0017]
The MEMS element 21 can be applied to a resonator, an optical modulator, an optical switch, a high frequency switch, and the like. This resonator can be applied to MEMS filters such as a high frequency filter and an intermediate frequency filter, and a sensor detection circuit.
[0018]
When the MEMS element 21 is applied to a resonator, the fixed electrode 26 serves as an output electrode, and the drive electrode 28 serves as a vibrating electrode that also serves as an input electrode. A signal obtained by superimposing a high frequency signal and a DC bias voltage is input to the vibrating electrode 28 through the wiring layer 27 from the input terminal. An output terminal is led out to the output electrode 26. In this resonator, when a high frequency signal having a target frequency and a DC bias voltage are superimposed and input to the vibration electrode 28, the vibration electrode 28 having a natural frequency determined by the length is generated between the output electrode 26 and the vibration electrode 28. Vibrates with electric power. Due to this vibration, the capacitance is output from the high-frequency signal output electrode 26 according to the time change of the capacitance between the output electrode 26 and the vibration electrode 28 and the DC bias voltage.
[0019]
Next, an embodiment of a method for manufacturing a MEMS element according to the present embodiment will be described with reference to FIGS.
First, as shown in FIG. 2A, a substrate 20 having a surface having an insulating film is prepared. In this example, a substrate 20 formed by forming an insulating film 23 in which a silicon oxide film 24 and a silicon nitride film 25 are laminated on a silicon substrate 22 is used.
Next, as shown in FIG. 2B, a first conductor layer to be a fixed side electrode and a wiring layer, in this example, a polysilicon film 34 is formed.
Next, as shown in FIG. 2C, the first polysilicon film 34 is selectively etched away by using a photolithography technique to form the fixed electrode 26 and the wiring layers 29 located on both sides thereof.
[0020]
Next, as shown in FIG. 2D, removal selectivity is provided for the thin sacrificial layer 34 on the substrate 20 including the fixed side electrode 26 and the wiring layer 27, in this example, the underlying silicon nitride film 25 and the polysilicon film. A silicon oxide film having (for example, different etching characteristics) is formed. Since the controllability of the film thickness of the sacrificial layer 34 is generally high, the sacrificial layer 34 is formed along the surface irregularities of the substrate 20 on which the fixed-side electrode 26 and the wiring layer 27 are formed. The sacrificial layer 34 is formed by, for example, a low pressure CVD (chemical vapor deposition) method.
[0021]
Next, as shown in FIG. 3E, a second conductor layer 29, which is a first conductor thin film constituting a part of the drive side electrode, in this example, a polysilicon film is formed by a low pressure CVD method.
[0022]
Next, as shown in FIG. 3F, a connection hole (contact hole) 35 reaching the wiring layer 27 is formed in the second conductor layer 29 and the sacrificial layer 34 therebelow. Thereafter, dirt in the connection hole 35, particularly a natural oxide film on the surface 36 of the wiring layer 27 is removed by washing. In this example, cleaning is performed with a hydrofluoric acid solution. During the cleaning with the hydrofluoric acid solution, the sacrificial layer 34 does not disappear because the surface is the protective layer of the second conductor layer 29. However, the sacrificial layer 34 that faces the connection hole 35 is slightly etched inward by cleaning with hydrofluoric acid. Since the surface of the wiring layer 27 is cleaned, good electrical connection between the third conductor layer 30 and the wiring layer 27 to be formed thereafter is ensured.
[0023]
Next, as shown in FIG. 3G, a third conductor layer 30 serving as a second conductor thin film constituting a part of the drive side electrode, in this example, a polysilicon film is formed by a low pressure CVD method. At this time, the third conductor layer 30 is electrically connected to the underlying wiring layer 27 through the connection hole 35. In addition, since the third conductor layer 30 is electrically connected to the wiring layer 27 and the second conductor layer 29, the driving composed of a first conductor thin film 29 and a second conductor thin film 30 described later. The side electrode 28 and the wiring layer 27 are electrically connected.
[0024]
Next, as shown in FIG. 3H, the second and third conductor layers 29 and 30 are patterned to form the drive-side electrode 28 composed of the first conductor thin film 29 and the second conductor thin film 30. . Next, the sacrificial layer 34 is removed, and a gap 31 is formed between the drive side electrode 28 and the fixed side electrode 26. In this example, the sacrificial layer 34 made of a silicon oxide film (SiO ₂ ) is removed with a hydrofluoric acid solution. Thus, the target MEMS element 21 is obtained.
[0025]
According to the manufacturing method of the MEMS element of the present embodiment, after forming the sacrificial layer 34, the second conductor layer 29 to be the first conductor thin film of the drive side electrode 28 is formed on the sacrificial layer 34. Then, since the connection hole 35 reaching the wiring layer 27 is formed in the sacrificial layer 34 and the second conductor layer 29, the sacrificial layer 34 is not lost during the subsequent cleaning with hydrofluoric acid in the connection hole 35. . In particular, even when the sacrificial layer 34 is formed with a nanometer-level film thickness, for example, about 10 nm or less, the sacrificial layer 34 is protected by the second conductor layer, that is, the hydrofluoric acid resistant polysilicon film 29. The sacrificial layer 34 is not lost by cleaning with hydrofluoric acid in the connection hole 35. Therefore, the MEMS element 21 having the gap 31 with a nanometer level gap between the driving side electrode 28 and the fixed side electrode 26 can be manufactured with high accuracy. In addition, since the film thickness control at the time of sacrificial layer deposition by LPCVD or the like is relatively high accuracy, the sacrificial layer can be stably formed even with a thin film of nm level by the manufacturing method of the present invention, Devices such as MEMS resonators having high signal transfer characteristics can be manufactured stably.
[0026]
In the above example, the first conductor layer 33, the second conductor layer 29, and the third conductor layer 30 are formed of a polysilicon film, but in addition, aluminum (Al), tungsten (W), chromium ( It can be formed of a metal film such as Cr) or nickel (Ni). The first, second, and third conductor layers 33, 29, and 30 can be formed of the same material film, or can be formed of different material films. It is also possible to form the layers with the different material films.
When the drive side electrode 28 is formed by selecting various material films, the natural frequency of the drive side electrode 28 can be appropriately selected.
[0027]
As described above, the MEMS element 21 obtained by the manufacturing method of the present embodiment includes a MEMS resonator applied to a filter, a sensor detection circuit, and the like, an optical MEMS such as a high-frequency switch, an optical switch, and an optical modulator. It can be used for an element or the like. When applied to an optical MEMS element, in order to increase the light reflection efficiency of the surface of the drive side electrode 28, it is preferable to form the film 30 of at least the second layer of the drive side electrode 28 with a metal film.
[0028]
As the sacrificial layer, amorphous silicon, photoresist, or the like can be used in addition to the silicon oxide film. In this case, materials for the insulating film 25, the electrodes 26 and 28, and the wiring layer 27 are selected accordingly. The etchant for removing the amorphous silicon can use XeF ₂ gas, and the etchant for removing the photoresist can use O ₂ plasma.
In the above example, the sacrificial layer is a silicon oxide film, and the inside of the connection hole is cleaned with a hydrofluoric acid solution. However, in the case of a sacrificial layer made of other materials, it can be cleaned with an etchant that removes the sacrificial layer.
[0029]
【The invention's effect】
According to the method for manufacturing a MEMS element according to the present invention, it is possible to manufacture a MEMS element in which the gap distance between the drive side electrode and the fixed side electrode is set to be ultrafine, particularly at a nanometer level. It is possible to prevent the sacrificial layer from disappearing in a cleaning step after the connection hole is formed in the sacrificial layer. Since the film thickness control at the time of sacrificial layer formation is relatively high accuracy, the sacrificial layer can be stably formed even by a nanometer level thin film by the manufacturing method of the present invention. Therefore, for example, a device such as a MEMS element resonator having high signal transfer characteristics can be stably manufactured.
When the driving side electrode is formed by selecting a polysilicon film or other metal film, for example, when applied to a resonator, the natural frequency of the driving side electrode can be set as appropriate.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of a MEMS element obtained by the manufacturing method of the present invention.
FIGS. 2A to 2D are process diagrams (part 1) showing an embodiment of a method for producing a MEMS device according to the present invention. FIGS.
FIGS. 3A to 3H are process diagrams (part 2) illustrating an embodiment of a method for producing a MEMS element according to the present invention. FIGS.
FIGS. 4A and 4B are configuration diagrams showing an example of a conventional MEMS element. FIGS.
FIGS. 5A to 5D are manufacturing process diagrams showing intervals between conventional MEMS elements. FIGS.
[Explanation of symbols]
20 .. Substrate, 21 .. MEMS element, 22 .. Silicon substrate, 23 .. Insulating film, 24 .. Silicon oxide (SiO ₂ ) film, 25 .. Silicon nitride (SiN) film, 26. 27 .... Wiring layer, 28 ... Drive side electrode, 29 ... First conductor thin film, 30 ... Second conductor thin film, 31 ... Air gap, 34 ... Sacrificial layer, 35 ... Connection hole

Claims (4)

Forming a first electrode having a removal selectivity with respect to a sacrificial layer and a wiring layer on a substrate;
Forming a sacrificial layer on the substrate including the first electrode and the wiring layer;
Forming a first conductor thin film on the sacrificial layer, and forming a connection hole reaching the wiring layer in the first conductor thin film and the sacrificial layer;
Cleaning the inside of the connection hole with an etchant that removes the sacrificial layer ;
Forming a second conductor thin film on the first conductor thin film so as to be electrically connected to the wiring layer via the connection hole;
Patterning the first and second conductive thin films to form a drivable second electrode comprising the first and second conductive thin films;
And a step of removing the sacrificial layer. A method of manufacturing a MEMS device, comprising: The method for manufacturing a MEMS element according to claim 1, wherein the sacrificial layer is a silicon oxide film. The first electrode and wiring layer, the first conductor thin film, and the second conductor thin film are both formed of the same conductive material or one of three layers made of a different conductive material from the other layers. The method of manufacturing a MEMS element according to claim 1, wherein: 2. The method of manufacturing a MEMS element according to claim 1, wherein the first electrode and wiring layer, the first conductor thin film, and the second conductor thin film are formed of a polysilicon film.

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