US20060063472A1

US20060063472A1 - Method for polishing substrate

Info

Publication number: US20060063472A1
Application number: US11/228,214
Authority: US
Inventors: Satoshi Matsumoto; Yuichi Kurimoto
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 2004-09-21
Filing date: 2005-09-19
Publication date: 2006-03-23
Also published as: JP2006093180A

Abstract

In a method for polishing a substrate, a substrate placed on a polishing pad bonded onto a platen is polished while the temperature of a surface of the polishing pad is monitored. An index of the amount of the substrate polished is calculated based on the monitored temperature of the polishing pad surface. When the calculated index of the amount of the substrate polished is below a previously set value, the substrate is detected as an abnormally polished substrate.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 on Patent Application No. 2004-272852 filed in Japan on Sep. 21, 2004, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

(1) Field of the Invention
The present invention relates to a substrate polishing method in which a substrate is polished while the temperature of a surface of a polishing pad is measured.
(2) Description of Related Art
In a known chemical mechanical polishing (CMP) technique in which a surface of a semiconductor wafer is polished, semiconductor wafers to be polished are subjected one after another to a polishing process and the polishing process is repeated at regular intervals. Even when trouble with equipment or variations of the time during which a semiconductor wafer is transferred make the interval between one polishing process and the next polishing process longer than usual, the next process is often successively carried out as long as the trouble with equipment is minor and the polishing processes are interrupted only for a short time of a few minutes.
In the CMP technique, a polishing time is typically used as a criterion for detecting an end point of polishing. It has been known that when a metal film is polished to form a buried interconnect, a point of change of the temperature of a surface of a polishing pad is used as the criterion (see Japanese Unexamined Patent Publication Nos. 7-94452 and 8-330261). When a semiconductor wafer is polished by rotating the platen and the carrier while supplying abrasives to a polishing pad bonded to a platen with a substrate that is supported by a carrier pressed against the polishing pad, the temperature of a surface of the polishing pad is measured by a sensor. The measured temperature of the polishing pad surface is always monitored using a monitoring tool connected to the sensor, thereby detecting a point of change of the measured temperature. When a metal film is polished to form a buried interconnect, the temperature of the polishing pad surface varies according to the type of the metal film to be polished. Therefore, the point of change of the surface temperature can be utilized as the criterion of end-point detection.
The utilization of the point of change of the temperature of the polishing pad surface as an end point of polishing is effective at polishing a metal film to form a buried interconnect but impossible in a polishing process in which a single metal film is to be polished, such as a polishing process for an insulating film. The reason for this is that in the above polishing process, such a significant change in temperature that can be considered as the end point does not occur.
Meanwhile, when the time interval between one polishing process and the next polishing process becomes longer than usual due to troubles with equipment and the transfer of semiconductor wafers, the temperature of a surface of a polishing pad at the start of the next process becomes lower than usual. The temperature of the polishing pad surface increases during polishing and then decreases during standby. This is repeated. In view of the above, as the standby time becomes longer than usual, the temperature of the polishing pad surface becomes lower.
In the CMP technique, a chemical action of the CMP depends on the temperature of a polishing pad surface. When the temperature is low, the polishing rate becomes low. Thus, when polishing is started under the condition that the temperature of the polishing pad surface is low, the polishing rate becomes low. Therefore, even when polishing is carried out for a normally set time, such an abnormality that part of a substrate is unpolished occurs in a product to be processed. Conventionally, in the case where the time during which polishing is interrupted is short, a polishing apparatus keeps being operated without checking the state of the polished product and is provided with no sensor for sensing the above abnormality.

SUMMARY OF THE INVENTION

The present invention has been made to solve the aforementioned problems, and an object of the present invention is to allow reliable elimination of a substrate that has been insufficiently polished in a substrate polishing process.
In order to achieve the above object, the present invention is configured such that a method for polishing a substrate is carried out while the temperature of a surface of a polishing pad is monitored.
A method for polishing a substrate according to a first aspect of the present invention includes the steps of: (a) polishing a substrate placed on a polishing pad bonded onto a platen while monitoring the temperature of a surface of the polishing pad; (b) calculating an index of the amount of the substrate polished on the basis of the monitored temperature of the polishing pad surface; and (c) detecting an abnormally polished substrate when the calculated index of the amount of the substrate polished is below a previously set value.
According to the substrate polishing method of the first aspect, information concerning the amount of the substrate polished can be easily obtained. Since an abnormality in the amount of the substrate polished can therefore be detected immediately after the polishing of the substrate, this makes it possible to remove a substrate having such an abnormality that part of the substrate is unpolished from a fabrication process.
In the method of the first aspect, the index of the amount of the substrate polished may be a value obtained by integrating the temperature of the polishing pad surface with respect to the time during which the substrate is polished, the average temperature of the polishing pad surface during the time during which the substrate is polished, or a value obtained by differentiating variations in the temperature of the polishing pad surface in the step (a).
Preferably, the method of the first aspect further includes the step (d) of, after the step (a), removing the polished substrate from on the polishing pad and replacing the polished substrate with an unpolished substrate, wherein a cycle of the steps (a), (b), (c), and (d) is carried out a plurality of times.
In the method of the first aspect, an alarm is preferably raised when the abnormally polished substrate is detected.
It is preferable that, in the method of the first aspect, the substrate is further polished when the abnormally polished substrate is detected.
A method for polishing a substrate according to a second aspect includes the steps of: (a) polishing a substrate placed on a polishing pad bonded onto a platen while monitoring the temperature of a surface of the polishing pad; and (b) calculating an index of the amount of the substrate polished on the basis of the monitored temperature of the polishing pad surface, wherein the step (b) is carried out simultaneously with the step (a), and the step (a) is carried out until the index of the amount of the substrate polished that has been calculated in the step (b) reaches a previously set value.
According to the method of the second aspect, the substrate can be polished until the amount of the substrate polished reaches a predetermined value. Since a shortage of the amount of the substrate to be polished is therefore not caused, a substrate having such an abnormality that part of the substrate is unpolished is not transferred to later process steps.
In the method of the second aspect, the index of the amount of the substrate polished is preferably a value obtained by integrating the temperature of the polishing pad surface with respect to the time during which the substrate is polished and may be the average temperature of the polishing pad surface during the time during which the substrate is polished.
Preferably, the method of the second aspect further includes the step (c) of, after the step (a), removing the polished substrate from on the polishing pad and replacing the polished substrate with an unpolished substrate, wherein a cycle of the steps (a) and (b) and the step (c) are carried out a plurality of times.
It is preferable that the method of the second aspect further includes the step of correcting the set value based on the index of the amount of the substrate polished that has been calculated in the step (b) after each completion of the cycle of the steps (a) and (b).
A method for polishing a substrate according to a third aspect of the present invention includes the steps of: (a) polishing a substrate placed on a polishing pad bonded onto a platen while monitoring the temperature of a surface of the polishing pad; and (b) replacing the polished substrate with an unpolished substrate by removing the polished substrate from on the polishing pad, wherein the steps (a) and (b) are successively carried out a plurality of times, the time required for the step (b) is measured, and when the time required for the step (b) is longer than a previously set time, the unpolished substrate is detected as an abnormally polished substrate.
According to the method of the third aspect, the abnormally polished substrate can be easily detected. This can prevent, with reliability, a substrate having such an abnormality that part of the substrate is unpolished from being transferred to later process steps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a polishing apparatus according to a first embodiment of the present invention.
FIG. 2 is a graph showing temperature variations at a polishing pad surface when intervals between polishing steps are fixed in a substrate polishing method of the first embodiment of the present invention.
FIG. 3 is a graph showing temperature variations at a polishing pad surface when intervals between polishing steps vary in the substrate polishing method of the first embodiment of the present invention.
FIG. 4 is a graph showing the comparison on temperature variations at a polishing pad surface between a polishing step after the usual standby time and a polishing step after a prolonged standby time in the substrate polishing method of the first embodiment of the present invention.
FIG. 5 is a graph showing the relationship between the average temperature of the polishing pad surface and the polishing rate in the substrate polishing method of the first embodiment of the present invention.
FIG. 6 is a schematic view showing another polishing apparatus according to the first embodiment of the present invention.
FIG. 7 is a graph showing the comparison on temperature variations at a polishing pad surface between a polishing step after the usual standby time and a polishing step after a prolonged standby time in a substrate polishing method of a first modification of the first embodiment of the present invention.
FIG. 8 is a graph showing the relationship between the standby time and the polishing rate in a substrate polishing method of a second modification of the first embodiment of the present invention.
FIG. 9 is a graph showing the progression of the temperature of a polishing pad surface in a substrate polishing method of a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment 1

A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 illustrates a polishing apparatus according to the first embodiment. As shown in FIG. 1, the polishing apparatus of this embodiment includes a platen 11 to which a polishing pad 12 is bonded and a carrier 14 for supporting a substrate 13. The substrate 13 is polished by rotating the platen 11 and the carrier 14 while supplying abrasives 15 to the polishing pad 12 with the substrate 13 pressed against the polishing pad 12.
The polishing apparatus further includes a sensor 16 for measuring the temperature of a surface of the polishing pad 12 and a monitoring tool 18 connected to the sensor 16. Therefore, the temperature of the polishing pad 12 surface can always be monitored. A part 17 of the polishing pad 12 to be measured in its surface temperature (hereinafter, referred to as “to-be-temperature-measured part 17”) is preferably set to overlap with a path through which the center of the substrate 13 travels on the polishing pad 12 during polishing. A non-contact radiation thermometer or the like is used as the sensor 16.
During polishing, the temperature of the polishing pad 12 surface increases due to the friction between the substrate 13 and the polishing pad 12. FIG. 2 illustrates the progression of the temperature of the polishing pad 12 surface. As shown in FIG. 2, polishing steps 21 and standby steps 22 are alternately carried out. In each polishing step 21, the temperature of the polishing pad 12 surface increases, and in each standby step 22, the temperature of the polishing pad 12 surface decreases.
When equipment operates normally, the polishing steps 21 are carried out at regular intervals, and the respective times required for each polishing step 21 and each standby step 22 are fixed. The temperatures of the polishing pad 12 surface at the starts of the polishing steps 21 become substantially equal to one another, and those at the completion of the polishing steps 21 become substantially equal to one another.
However, when the next substrate is transferred later than usual due to troubles with equipment or the like, this increases the standby time and the intervals between polishing steps. In some of processes for fabricating a semiconductor device, the processing time for the previous step is not fixed so that the intervals between polishing steps are not originally regular.
FIG. 3 illustrates the progression of the temperature of the polishing pad 12 surface when the intervals between polishing steps are not regular. In a standby step 24 in which the standby time becomes longer than usual due to troubles, the temperature of the polishing pad 12 surface becomes lower than usual. The next polishing step 23 is started under the condition that the temperature of the polishing pad 12 surface is lower than usual.
FIG. 4 illustrates, in the same coordinate plane, temperature variations at the polishing pad 12 surface in the polishing step 21 after a normal standby step 22 and temperature variations at the polishing pad 12 surface in the polishing step 23 after the standby step 24 in which the standby time is longer than usual.
When the standby time is longer than usual, the temperature of the polishing pad 12 surface at the beginning of polishing becomes lower than usual. As a result, the average temperature of the polishing pad 12 surface during polishing becomes lower than usual.
FIG. 5 illustrates the relationship between the average temperature of the polishing pad 12 surface during polishing and the polishing rate. As shown in FIG. 5, with reduction in the average temperature of the polishing pad 12 surface, the polishing rate is decreasing. Therefore, when the polishing time is fixed, the amount of the substrate 13 polished decreases with reduction in the average temperature of the polishing pad 12 surface. In view of the above, when the standby time becomes longer than usual so that polishing is started under the condition that the temperature of the polishing pad 12 surface is lower than usual, there is a high possibility that a surface of the substrate 13 is not sufficiently polished, leading to such a quality abnormality that part of the substrate 13 is unpolished. As seen from the above, the average temperature of the polishing pad 12 surface during polishing is used as an index of the amount of the substrate 13 polished.
In this embodiment, the average temperature of the polishing pad 12 surface during polishing is calculated, as an index of the amount of the substrate 13 polished, by constantly monitoring the temperature of the polishing pad 12 surface. When the calculated index is smaller than a previously set threshold value, the processed substrate 13 is identified and eliminated. In this way, the substrate 13 that may have such a quality abnormality that part of the substrate 13 is unpolished can be eliminated from a fabrication line with reliability. After the eliminated substrate 13 is separately checked for unpolished part of the substrate 13 or other abnormalities, necessary handling is carried out.
The substrate 13 is manually eliminated most simply by displaying the presence of an abnormality on a screen of a polishing apparatus or by raising an alarm or the like utilizing a communication line or the like. Alternatively, the substrate 13 may be eliminated by an automatic substrate transport apparatus or other apparatuses.
Instead of the average temperature of the polishing pad 12 surface, a value obtained by integrating the temperature of the polishing pad 12 surface with respect to the polishing time may be used as all index of the amount of the substrate 13 polished.
Although in this embodiment an apparatus for polishing a substrate by rotating a pad and the substrate is used as an example, the polishing method of this embodiment can be applied also to a polishing apparatus of a linear polishing system shown in FIG. 6.
As shown in FIG. 6, the polishing apparatus of the linear polishing system polishes a substrate in the following manner. While abrasives 64 are supplied to a polishing pad 61 bonded to a belt with a substrate 62 that is supported by a carrier 63 pressed against the polishing pad 61, the belt is driven to horizontally move the polishing pad 61 and the carrier 63 is rotated. The temperature of the polishing pad 61 surface is measured by a sensor 65. The measured surface temperature is always monitored using a monitoring tool 67 connected to the sensor 65. A to-be-temperature-measured part 66 of the polishing pad 61 to be measured in its surface temperature is preferably set to overlap with a path through which the center of the substrate 62 travels on the polishing pad 61 during polishing. A non-contact radiation thermometer or the like need be used as the sensor 65.

Modification 1 of Embodiment 1

A first modification of the first embodiment of the present invention will be described hereinafter. In this modification, the rate of change of the temperature of a polishing pad 12 surface is used as an index of the amount of a substrate polished.
FIG. 7 is a graph showing the comparison on temperature variations at a polishing pad surface between a polishing step after the usual standby time and a polishing step after a prolonged standby time in a substrate polishing method of a first modification of the first embodiment of the present invention. In FIG. 7, the temperature variations at the polishing pad surface in the polishing step after the usual standby time and those at the polishing pad surface in the polishing step after the prolonged standby time are shown by a solid line and broken lines, respectively. The rate of change in the temperature of the polishing pad 12 surface in the polishing step after the usual standby time becomes smaller than that in the polishing step after the prolonged standby time Therefore, a substrate that may have been insufficiently polished can be detected in the following manner: In a time interval 93 in which the temperature of the polishing pad 12 surface is increasing immediately after the start of polishing, the slope of the rise in the temperature of the polishing pad 12 surface, i.e., a differential value, is calculated in real time, and the calculated slope of the temperature variations is compared with a previously set threshold value.

Modification 2 of Embodiment 1

A second modification of the first embodiment of the present invention will be described hereinafter. With an increase in the intervals between polishing steps, the temperature of the polishing pad 12 surface is reduced. This increases the possibility of such an abnormality that part of a substrate is unpolished. FIG. 8 illustrates the relationship between the standby time between polishing steps and the polishing rate. As shown in FIG. 8, with an increase in the standby time, the polishing rate is reduced.
In view of the above, when the standby time between polishing steps is always monitored and a substrate processed after the standby time exceeding a previously set threshold value is eliminated, this can prevent a substrate that may have such an abnormality that part of the substrate is unpolished from being transferred to the next step.
A standby time beyond which an abnormality is caused is determined as a threshold value of the standby time on the basis of correlation data between the polishing rate and the standby time.

Embodiment 2

A second embodiment of the present invention will be described hereinafter. In a polishing method of the second embodiment, a substrate is polished by the same polishing apparatus as in the first embodiment until an index of the amount of the substrate polished reaches a previously set value, thereby preventing a substrate with an abnormality from being produced.
FIG. 9 illustrates temperature variations of the polishing pad 12 surface according to this embodiment. In a polishing step 74 executed after the prolonged standby time, the temperature of the polishing pad 12 surface at the start of the polishing step 74 becomes lower than in a polishing step 73 executed after the usual standby time and the temperature rise also becomes slower than in the polishing step 73. However, in this embodiment, a substrate is polished until the integral of the temperature of the polishing pad 12 surface with respect to the polishing time reaches a previously set value. Therefore, the amount of the substrate 13 polished in the polishing step 73 after the usual standby time becomes substantially equal to the amount of the substrate 13 polished in the polishing step 74 after the prolonged standby time. Thus, in such cases that the standby time becomes longer than usual due to minor troubles or the like or the standby time is not originally fixed because of an inconstant processing time of the previous step, even if the temperature of the polishing pad 12 surface becomes low so that the polishing rate becomes low, such an abnormality that part of the substrate is unpolished is not caused.
According to the method of this embodiment, an end point at which polishing is completed is detected using, as an index of the amount of a substrate polished, the integral of the temperature of a polishing pad surface during polishing with respect to the polishing time. This method is effective as a method for detecting an end point of polishing when a single film is to be polished and therefore temperature variations of the polishing pad surface during polishing is small, such as when an insulating film is to be polished. Although a target index of the amount of the substrate polished may be previously set, it may be set by feeding forward indices for several products processed in recent polishing steps. Furthermore, the end point can be detected according to the type of a semiconductor device to be fabricated and the process step by using, for a program and recording medium for detecting an end point, a method for determining the polishing time of the present invention.
Instead of the integral of the temperature of a polishing pad surface with respect to the polishing time, the average temperature of the polishing pad surface during polishing may be used as an index of the amount of a substrate polished.
As described above, the method for polishing a substrate of the present invention is useful as a method in which a substrate is polished while the temperature of a polishing pad surface is measured, thereby certainly eliminating a substrate with such an abnormality that part of the substrate is unpolished.

Claims

1. A method for polishing a substrate, said method comprising the steps of:

(a) polishing a substrate placed on a polishing pad bonded onto a platen while monitoring the temperature of a surface of the polishing pad;

(b) calculating an index of the amount of the substrate polished on the basis of the monitored temperature of the polishing pad surface; and

(c) detecting an abnormally polished substrate when the calculated index of the amount of the substrate polished is below a previously set value.

2. The method of claim 1, wherein

the index of the amount of the substrate polished is a value obtained by integrating the temperature of the polishing pad surface with respect to the time during which the substrate is polished.

3. The method of claim 1, wherein

the index of the amount of the substrate polished is the average temperature of the polishing pad surface during the time during which the substrate is polished.

4. The method of claim 1, wherein

the index of the amount of the substrate polished is a value obtained by differentiating variations in the temperature of the polishing pad surface in the step (a).

5. The method of claim 1 further comprising the step (d) of, after the step (a), removing the polished substrate from on the polishing pad and replacing the polished substrate with an unpolished substrate,

wherein a cycle of the steps (a), (b), (c), and (d) is carried out a plurality of times.

6. The method of claim 1, wherein

an alarm is raised when the abnormally polished substrate is detected.

7. The method of claim 1, wherein

the substrate is further polished when the abnormally polished substrate is detected.

8. A method for polishing a substrate, said method comprising the steps of:

(a) polishing a substrate placed on a polishing pad bonded onto a platen while monitoring the temperature of a surface of the polishing pad; and

(b) calculating an index of the amount of the substrate polished on the basis of the monitored temperature of the polishing pad surface,

wherein the step (b) is carried out simultaneously with the step (a), and

the step (a) is carried out until the index of the amount of the substrate polished that has been calculated in the step (b) reaches a previously set value.

9. The method of claim 8, wherein

10. The method of claim 8, wherein

11. The method of claim 8 further comprising the step (c) of, after the step (a), removing the polished substrate from on the polishing pad and replacing the polished substrate with an unpolished substrate,

wherein a cycle of the steps (a) and (b) and the step (c) are carried out a plurality of times.

12. The method of claim 11 further comprising the step of correcting the set value based on the index of the amount of the substrate polished that has been calculated in the step (b) after each completion of the cycle of the steps (a) and (b).

13. A method for polishing a substrate, said method comprising the steps of:

(b) replacing the polished substrate with an unpolished substrate by removing the polished substrate from on the polishing pad,

wherein the steps (a) and (b) are successively carried out a plurality of times,

the time required for the step (b) is measured, and

when the time required for the step (b) is longer than a previously set time, the unpolished substrate is detected as an abnormally polished substrate.