How to calibrate an acoustic sensor

Abstract

To provide a method capable of accurately calibrating an acoustic sensor arranged on a polishing device.SOLUTION: A calibration method of an acoustic sensor comprises: acquiring a polishing sound of a substrate W using an acoustic sensor 44; extracting at least two feature sounds having feature frequency from the acquired polishing sound; outputting at least two feature sounds from a sound source 45 connected with one of a polishing table 3, the acoustic sensor 44, and a substrate holding device 1, and inputting these at least two feature sounds to the acoustic sensor 44; and subsequently calibrating an output value of the acoustic sensor so that an output value of the acoustic sensor 44 with respect to the at least two feature sounds falls within an allowable range.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for calibrating an acoustic sensor, and more particularly to a method for calibrating an acoustic sensor disposed in a polishing apparatus. [Background technology]

[0002] A CMP (Chemical Mechanical Polishing) machine is a polishing machine that polishes the surface of a substrate such as a wafer in the manufacture of semiconductor devices. The CMP machine holds the substrate with a polishing head, rotates the substrate, and polishes the substrate surface by pressing the substrate against a polishing pad on a rotating polishing table. During polishing, a polishing liquid (slurry) is supplied to the polishing pad, and the surface of the substrate is planarized by the chemical action of the polishing liquid and the mechanical action of the abrasive grains contained in the polishing liquid.

[0003] In such polishing apparatus, an acoustic sensor (e.g., an ultrasonic sensor, an AE sensor) may be used to detect the polishing state of the substrate. Examples of the polishing state of the substrate detected by the acoustic sensor include the end point of polishing the substrate, an abnormality in polishing the substrate, etc. The acoustic sensor is disposed, for example, in a polishing chamber in which a polishing table is disposed, and collects polishing sounds generated when the substrate is polished. The polishing apparatus determines the polishing state of the substrate (e.g., the end point of polishing the substrate) based on the collected polishing sounds. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-163100 A Summary of the Invention [Problem to be solved by the invention]

[0005] After a certain amount of time has passed since the acoustic sensor was first used, the measurement value of the acoustic sensor (i.e., the output value of the acoustic sensor) may deviate. In addition, the output value of the acoustic sensor may differ depending on the installation state (e.g., the installation position) of the acoustic sensor in each polishing machine. For this reason, it is necessary to calibrate the acoustic sensor periodically.

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a method capable of accurately calibrating an acoustic sensor disposed in a polishing apparatus. [Means for solving the problem]

[0007] In one aspect, there is provided a method for calibrating an acoustic sensor provided in a polishing apparatus that polishes a substrate held by a substrate holding device by pressing the substrate against a polishing pad attached to a polishing table, the method comprising: acquiring a polishing sound of the substrate using the acoustic sensor; extracting at least two characteristic sounds having characteristic frequencies from the acquired polishing sounds; outputting the at least two characteristic sounds from a sound source connected to any one of the polishing table, the acoustic sensor, and the substrate holding device; inputting the at least two characteristic sounds to the acoustic sensor; and calibrating an output value of the acoustic sensor such that the output value of the acoustic sensor for the at least two characteristic sounds falls within an acceptable range.

[0008] In one embodiment, the acoustic sensor is an AE sensor attached to the polishing table, and the sound source is disposed at a position on the polishing pad or the polishing table corresponding to a polishing position of the substrate. In one embodiment, the sound source is an AE sensor for a sound source having the same configuration as the AE sensor. In one embodiment, the sound source is disposed directly above the AE sensor.

[0009] In one embodiment, the acoustic sensor is an ultrasonic sensor coupled to an arm supporting the substrate holding device, and the sound source is positioned on the polishing pad or polishing table at a position corresponding to the polishing position of the substrate. In one aspect, the acoustic sensor is an ultrasonic sensor coupled to an arm that supports the substrate holder, and the sound source is coupled to the acoustic sensor.

[0010] In one aspect, the acoustic sensor is attached to the substrate holding apparatus and the sound source is attached to the substrate holding apparatus. In one embodiment, the acoustic sensor is an AE sensor. In one embodiment, the sound source is an AE sensor for a sound source having the same configuration as the AE sensor. In one reference example, the step of inputting the at least two characteristic sounds to the acoustic sensor is performed in a state in which the substrate is held by the substrate holding device.

[0011] In one embodiment, an alarm is issued when the output value of the acoustic sensor for the at least two characteristic sounds exceeds an upper threshold or a lower threshold. Effect of the Invention

[0012] According to the present invention, the acoustic sensor is calibrated based on the polishing sound generated during polishing of the substrate, so that the acoustic sensor can be accurately calibrated based on the actual polishing sound. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing a polishing apparatus according to one embodiment. [Diagram 2] FIG. 2 is a graph showing an example of a grinding sound acquired by an acoustic sensor. [Diagram 3] FIG. 3 is a schematic diagram for explaining a method for calibrating an acoustic sensor according to an embodiment. [Figure 4] FIG. 4 is a schematic diagram for explaining a calibration method of an acoustic sensor according to another embodiment. [Diagram 5] FIG. 5 is a schematic diagram for explaining a calibration method of an acoustic sensor according to still another embodiment. [Figure 6]FIG. 6 is a schematic diagram for explaining a calibration method of an acoustic sensor according to still another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a schematic diagram showing a polishing apparatus according to one embodiment. As shown in Fig. 1, the polishing apparatus includes a polishing table 3 that supports a polishing pad 2, a polishing head (substrate holding device) 1 that holds a wafer W, which is an example of a substrate, and presses it against the polishing pad 2, a table motor 6 that rotates the polishing table 3, a polishing liquid supply nozzle 5 for supplying a polishing liquid such as slurry onto the polishing pad 2, and a control device 9 for controlling the operation of the polishing apparatus. The upper surface of the polishing pad 2 constitutes a polishing surface 2a for polishing the wafer W.

[0015] The polishing head 1 is connected to a head shaft 10, and the head shaft 10 is connected to a polishing head motor (not shown) via a connecting means such as a belt. The polishing head motor rotates the polishing head 1 together with the head shaft 10 in the direction indicated by the arrow. The polishing table 3 is connected to a table motor 6, and the table motor 6 is configured to rotate the polishing table 3 and the polishing pad 2 in the direction indicated by the arrow. The rotation direction of the polishing head 1 and the polishing table 3 is not limited to this embodiment. In one embodiment, the polishing head 1 and the polishing table 3 may be configured to rotate in the direction opposite to the direction indicated by the arrow in FIG. 1.

[0016] The wafer W is polished as follows. While the polishing table 3 and polishing head 1 are rotated in the direction indicated by the arrow in Fig. 1, a polishing liquid is supplied from a polishing liquid supply nozzle 5 to the polishing surface 2a of the polishing pad 2 on the polishing table 3. While the wafer W is rotated by the polishing head 1, the wafer W is pressed against the polishing surface 2a of the polishing pad 2 by the polishing head 1 with the polishing liquid present on the polishing pad 2. The surface of the wafer W is polished by the chemical action of the polishing liquid and the mechanical action of the abrasive grains contained in the polishing liquid or the polishing pad 2.

[0017] 1 has an acoustic sensor 44 for detecting the polishing state of the wafer W. This type of acoustic sensor 44 is, for example, an ultrasonic sensor or an AE (Acoustic Emission) sensor. The acoustic sensor 44 is disposed in a polishing chamber in which the polishing head 1, polishing table 3, etc. are disposed, and collects polishing sounds generated when the wafer W is polished.

[0018] The acoustic sensor 44 is connected to the control device 9 via a sound processing device 49. The sound processing device 49 includes an amplifier 49a that amplifies the sound signal collected by the acoustic sensor 44, and a filter 49b that removes noise from the sound signal amplified by the amplifier 49a. The control device 9 is configured to receive the sound signal collected by the acoustic sensor 44 and processed by the sound processing device 49. Furthermore, the control device 9 is configured to determine the polishing state of the wafer W, such as the end point of polishing the wafer W and / or a polishing abnormality, based on the polishing sound of the wafer W generated during polishing of the wafer W. A method for calibrating the acoustic sensor 44 will be described below.

[0019] In calibrating the acoustic sensor 44, the control device 9 first acquires the polishing sound of the wafer W using the acoustic sensor 44, and extracts at least two characteristic sounds having characteristic frequencies from the acquired polishing sound. In this specification, a characteristic sound is a sound having a frequency that has a characteristic peak among the polishing sounds acquired by the acoustic sensor 44. When acquiring the polishing sound of the wafer W, the control device 9 accumulates the output value of the acoustic sensor 44 for a predetermined period of time, for example, and determines the polishing sound of the wafer W by averaging the output value of the acoustic sensor 44 for each frequency.

[0020] Fig. 2 is a graph showing an example of a grinding sound acquired by an acoustic sensor. In Fig. 2, the vertical axis represents sound pressure, and the horizontal axis represents frequency. As shown in Fig. 2, the grinding sound acquired by the acoustic sensor 44 has a plurality of characteristic peaks Pk. The control device selects at least two peaks Pk from among these peaks Pk, and determines the sound of the frequency corresponding to the selected peaks Pk as the characteristic sound. Furthermore, the control device 9 stores the frequency of the characteristic sound and the sound pressure corresponding to this frequency.

[0021] Next, a sound source is connected to any one of the polishing table 3, the acoustic sensor 44, and the polishing head 1. Furthermore, at least two characteristic sounds described above are output from this sound source, and these at least two characteristic sounds are collected (input) into the acoustic sensor 44. The control device 9 acquires the output value of the acoustic sensor 44 to which the characteristic sounds have been input, and calibrates the output value of the acoustic sensor so that all of these output values ​​fall within a predetermined tolerance range. The control device 9 stores the predetermined tolerance range in advance.

[0022] Fig. 3 is a schematic diagram for explaining a method for calibrating an acoustic sensor according to an embodiment. The acoustic sensor 44 shown in Fig. 3 is an AE sensor attached to the lower surface of the polishing table 3. In this embodiment, the acoustic sensor 44 collects the polishing sound of the wafer W while rotating together with the polishing table 3 during polishing of the wafer W. In one embodiment, the acoustic sensor 44 may be embedded in the polishing table 3.

[0023] 3, when calibrating an acoustic sensor 44, which is an AE sensor attached to the underside of the polishing table 3 (or embedded in the polishing table 3), a sound source 45 is placed on the polishing surface 2a of the polishing pad 2 supported on the polishing table 3. By this operation, the sound source 45 is connected to the polishing table 3 via the polishing pad 2.

[0024] In one embodiment, the polishing pad 2 may be removed and the sound source 45 may be directly coupled to the top surface of the polishing table 3. The polishing pad 2 is a consumable item and is a member that is periodically maintained or replaced. By performing a calibration process for the acoustic sensor 44 during the maintenance or replacement work of the polishing pad 2, the downtime of the polishing apparatus can be reduced.

[0025] The sound source 45 may be connected to any position on the polishing table 3. For example, a holder (not shown) for holding the sound source 45 may be fixed to the side or underside of the polishing table 3, and the sound source 45 may be held by the holder, or the sound source 45 may be directly attached to the side or underside of the polishing table 3.

[0026] A signal generator 46 for outputting a characteristic sound from the sound source 45 is connected to the sound source 45, and the signal generator 46 is connected to the control device 9. As described above, the control device 9 inputs a signal corresponding to the acquired characteristic sound from the signal generator 46 to the sound source 45, thereby causing the sound source 45 to output the characteristic sound at the acquired sound pressure. Examples of the signal input from the signal generator 46 to the sound source 45 include a sine wave, a square wave, and a burst wave.

[0027] The acoustic sensor 44 collects the characteristic sound output from the sound source 45. That is, the characteristic sound output from the sound source 45 is input to the acoustic sensor 44, and the output value (sound pressure) of the acoustic sensor 44 for the characteristic sound is input to the control device 9. The allowable range for the output value of the acoustic sensor 44 is input in advance to the control device 9, and the control device 9 compares all output values ​​of the acoustic sensor 44 to which the characteristic sound has been input with the allowable range. If there is no output value that deviates from the allowable range, the control device 9 ends the calibration process of the acoustic sensor 44.

[0028] If even one output value deviates from the allowable range, the control device 9 calculates a conversion equation for correction of the output value of the acoustic sensor 44 so that all output values ​​fall within the allowable range. The conversion equation for correction is, for example, an approximation line determined by the least squares method based on the output value (sound pressure) of the acoustic sensor 44 for the frequency of the characteristic sound. The control device 9 changes the slope and offset value of the conversion equation for correction, which is an approximation line, so that all output values ​​of the acoustic sensor 44 fall within the allowable range. The offset value corresponds to the y-intercept of the approximation line drawn on a graph with the output value of the acoustic sensor 44 on the vertical axis (y-axis) and the frequency on the horizontal axis (x-axis).

[0029] When the control device 9 selects two characteristic sounds, the above-mentioned conversion equation for correction is expressed by a straight line passing through the output values ​​of the two characteristic sounds. In this case, the control device 9 changes the slope and offset value of the conversion equation for correction so that the two output values ​​of the acoustic sensor 44 match the sound pressures of the characteristic sounds.

[0030] According to such a calibration process, the acoustic sensor 44 is calibrated based on the polishing sound generated during polishing of the wafer W. As a result, the acoustic sensor 44 can be accurately calibrated based on the actual polishing sound.

[0031] The control device 9 may store in advance upper and lower threshold values ​​set to a range wider than the above-mentioned allowable range. In this case, the control device 9 is configured to issue an alarm when any one of the output values ​​of the acoustic sensor 44 exceeds the upper or lower threshold value. This alarm allows the worker to quickly recognize improper installation or a malfunction of the acoustic sensor 44 and / or the sound source 45.

[0032] In one embodiment, after the calibration process is completed, the control device 9 may be caused to execute a confirmation operation. The confirmation operation is a process for confirming whether or not the calibration of the acoustic sensor 44 has been reliably performed. Specifically, the characteristic sound is output again from the sound source 45, and the acoustic sensor 44 is caused to output an output value for this characteristic sound. The control device 9 inputs the output value from the acoustic sensor 44 into the post-calibration conversion formula to obtain the post-calibration output value of the acoustic sensor 44. Furthermore, the control device 9 confirms whether or not the post-calibration output value of the acoustic sensor 44 is within an allowable range. If any characteristic sound falls outside the allowable range, the control device 9 may issue an alarm.

[0033] In the calibration process of the acoustic sensor 44, the grinding sound is simulated using the sound source 45. Therefore, in this embodiment, the sound source 45 is preferably an AE sensor having the same configuration as the acoustic sensor 44. This allows the characteristic sound output by the sound source 45 to be accurately simulated by the characteristic sound collected by the acoustic sensor 44.

[0034] Furthermore, it is preferable to place the sound source 45 at a position corresponding to the actual polishing position of the wafer W. Specifically, it is preferable to place the sound source 45 directly below the center of the polishing head 1 on the polishing pad 2 or the polishing table 3.

[0035] Placing the sound source 45 as close as possible to the acoustic sensor 44 prevents the acoustic sensor 44 from picking up extraneous noise during the calibration process. Therefore, the sound source 45 may be located on the polishing pad 2 or polishing table 3 at a position corresponding to directly above the acoustic sensor 44 (see the two-dot chain line in FIG. 3).

[0036] 4 is a schematic diagram for explaining a method for calibrating an acoustic sensor according to another embodiment. Since the configuration of this embodiment that is not particularly explained is similar to the configuration of the above-mentioned embodiment, the duplicated explanation will be omitted.

[0037] In order to collect accurate polishing sounds, the acoustic sensor 44 is preferably disposed near the polishing position of the wafer W. In the embodiment shown in FIG. 4, the acoustic sensor 44 is connected to the head arm 15 that supports the head shaft 10 to which the polishing head 1 is connected. Specifically, the acoustic sensor 44 is attached to the tip of a sensor arm 48 extending from the head arm 15. With this configuration, the acoustic sensor 44 can be disposed near the polishing position of the wafer W, and the distance between the acoustic sensor 44 and the polishing position of the wafer W can be kept constant. Furthermore, by attaching the acoustic sensor 44 to the sensor arm 48 that is connected to the head arm 15, space saving is achieved, and the acoustic sensor 44 is prevented from getting in the way of an operator during maintenance of the polishing pad 2, etc.

[0038] Such an acoustic sensor 44 is, for example, an ultrasonic sensor. The calibration process of the acoustic sensor 44, which is an ultrasonic sensor, is similar to the calibration process of the acoustic sensor 44, which is an AE sensor, described above. That is, the control device 9 first acquires the polishing sound of the wafer W using the acoustic sensor 44, which is an ultrasonic sensor, and extracts at least two characteristic sounds from the acquired polishing sound. Next, the sound source 45 is connected to the polishing table 3. The sound source 45 may be connected to the polishing table 3 via the polishing pad 2, or may be directly connected to the polishing table 3.

[0039] Furthermore, at least two characteristic sounds are output from this sound source 45, and these at least two characteristic sounds are collected (input) into the acoustic sensor 44. The control device 9 acquires the output value of the acoustic sensor 44 to which the characteristic sounds have been input, and calibrates the output value of the acoustic sensor 44 so that all of these output values ​​fall within a predetermined tolerance range. When calibrating the output value of the acoustic sensor 44, the control device 9 calculates a conversion equation for correction of the output value of the acoustic sensor 44, and changes the slope and offset value of the conversion equation for correction.

[0040] In this embodiment, it is also preferable to place the sound source 45 at a position corresponding to the actual polishing position of the wafer W. Specifically, it is preferable to place the sound source 45 directly below the center of the polishing head 1 on the polishing pad 2 or the polishing table 3.

[0041] Fig. 5 is a schematic diagram for explaining a method for calibrating an acoustic sensor according to still another embodiment. The configuration of this embodiment that is not particularly explained is similar to the configuration of the above-mentioned embodiment, so that the overlapping explanation is omitted. The embodiment shown in Fig. 5 is a modified example of the embodiment shown in Fig. 4.

[0042] 5, the sound source 45 is an AE sensor, and is connected to the acoustic sensor 44 via a bracket 50. In this case, it is not necessary to remove the sound source 45 from the acoustic sensor 44 even during polishing of the wafer W. Therefore, the calibration process of the acoustic sensor 44 can be performed under conditions that are almost the same as the actual polishing conditions of the wafer W.

[0043] 6 is a schematic diagram for explaining a method for calibrating an acoustic sensor according to still another embodiment. Since the configuration of this embodiment that is not particularly explained is similar to the configuration of the above-mentioned embodiment, the duplicated explanation will be omitted.

[0044] In the embodiment shown in Fig. 6, the acoustic sensor 44 is attached to the polishing head 1. Fig. 6 shows an example in which the acoustic sensor 44 is attached to the outer surface of the polishing head 1. In one embodiment, the acoustic sensor 44 may be embedded in the polishing head 1. The acoustic sensor 44 may be, for example, an ultrasonic sensor or an AE sensor.

[0045] When performing a calibration process for the acoustic sensor 44 attached to the polishing head 1, a sound source 45 is attached to the polishing head 1. In the illustrated example, the sound source 45 is attached to the bottom surface of the polishing head 1. In one embodiment, the sound source 45 may be attached to the side or top surface of the polishing head 1. This sound source 45 may be an AE sensor.

[0046] In this case as well, the control device 9 first acquires the polishing sound of the wafer W using the acoustic sensor 44 attached to the polishing head 1, and extracts at least two characteristic sounds from the acquired polishing sound. Next, the sound source 45 is connected to the polishing head 1. Furthermore, at least two characteristic sounds are output from this sound source 45, and these at least two characteristic sounds are collected (input) into the acoustic sensor 44. The control device 9 acquires the output value of the acoustic sensor 44 to which the characteristic sounds have been input, and calibrates the output value of the acoustic sensor 44 so that all of these output values ​​are within a predetermined tolerance range. When calibrating the output value of the acoustic sensor 44, the control device 9 calculates a conversion equation for correction of the output value of the acoustic sensor 44, and changes the slope and offset value of the conversion equation for correction.

[0047] Even with this configuration, the calibration process of the acoustic sensor 44 can be performed under conditions that are almost identical to the actual polishing conditions of the wafer W. During the calibration process of the acoustic sensor 44, it is preferable to have the polishing head 1 hold the wafer W in order to more accurately simulate the actual polishing conditions of the wafer W.

[0048] The above-described embodiments have been described for the purpose of enabling a person having ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments are naturally possible for a person skilled in the art, and the technical idea of ​​the present invention can be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be interpreted in the broadest scope according to the technical idea defined by the claims. [Explanation of symbols]

[0049] 1 Polishing head 2 Polishing Pads 3 Polishing table 5 Polishing fluid supply nozzle 6 Table Motor 9 Control device 10 Head shaft 15 Head Arm 44 Acoustic Sensor 45 Sound Sources 46 Signal Generator 48 Sensor Arm 49 Sound Processing Device 50 Bracket

Claims

1. A method for calibrating an acoustic sensor provided in a polishing apparatus that polishes a substrate by pressing the substrate held by a substrate holding device against a polishing pad attached to a polishing table, comprising the steps of: Using the acoustic sensor, obtain a polishing sound of the substrate; Extracting at least two characteristic sounds having characteristic frequencies from the acquired polishing sound; outputting the at least two characteristic sounds from a sound source connected to any one of the polishing table, the acoustic sensor, and the substrate holding device, and inputting the at least two characteristic sounds to the acoustic sensor; calibrating an output value of the acoustic sensor for the at least two characteristic sounds so that the output value of the acoustic sensor falls within an acceptable range; The method, wherein the at least two characteristic sounds are sounds at frequencies having characteristic peaks among the grinding sounds acquired by the acoustic sensor.

2. the acoustic sensor is an AE sensor attached to the polishing table, The method of claim 1 , wherein the acoustic source is disposed at a position on the polishing pad or polishing table corresponding to a polishing position of the substrate.

3. The method according to claim 2 , wherein the sound source is an AE sensor for the sound source having the same configuration as the AE sensor.

4. The method according to claim 2 or 3, wherein the sound source is positioned directly above the AE sensor.

5. the acoustic sensor is an ultrasonic sensor coupled to an arm supporting the substrate holding device; The method of claim 1 , wherein the acoustic source is disposed at a position on the polishing pad or polishing table corresponding to a polishing position of the substrate.

6. the acoustic sensor is an ultrasonic sensor coupled to an arm supporting the substrate holding device; The method of claim 1 , wherein the sound source is coupled to the acoustic sensor.

7. The acoustic sensor is attached to the substrate holding device, The method of claim 1 , wherein the acoustic source is attached to the substrate holder.

8. The method of claim 7 , wherein the acoustic sensor is an AE sensor.

9. The method according to claim 8 , wherein the sound source is an AE sensor for the sound source having the same configuration as the AE sensor.

10. The method according to claim 1 , further comprising issuing an alarm if the output values ​​of the acoustic sensor for the at least two characteristic sounds exceed an upper threshold or a lower threshold.

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