Polishing device and polishing method

Abstract

The present invention pertains to a technology for polishing a wafer by pressing a polishing tool against the wafer which is rotating, and in particular, to a technology for detecting a polishing end point of the wafer. This polishing device comprises a vibration analysis unit (70) that detects a polishing end point of a wafer (W) on the basis of a vibration of a polishing head (2). The vibration analysis unit (70) is configured to: extract, by a filter (75), a modulated high-frequency vibration from a vibration detection signal indicating the vibration of the polishing head (2); generate an envelope waveform by performing envelope processing on a modulated amplitude waveform indicating a temporal change in amplitude of the modulated high-frequency vibration; generate an amplitude spectrum by performing Fourier transform processing on the envelope waveform; and detect the polishing end point of the wafer (W) on the basis of a temporal change in amplitude of the amplitude spectrum in a target frequency band.

Description

Grinding apparatus and grinding method

[0001] The present invention relates to a technique for grinding a wafer by pressing a grinding tool against a rotating wafer, and particularly to a technique for detecting a grinding end point of a wafer.

[0002] In the manufacturing process of semiconductor devices, various materials are formed into films on a wafer. For this reason, unnecessary films are formed on the peripheral edge of the wafer. The unnecessary film on the peripheral edge of the wafer peels off from the wafer during wafer conveyance, adheres to devices on the wafer, and reduces the yield. Therefore, in order to remove the unnecessary film from the peripheral edge of the wafer, grinding of the peripheral edge of the wafer is performed by a grinding apparatus. This type of grinding apparatus grinds the peripheral edge of the wafer by pressing an abrasive tape against the peripheral edge of the wafer while rotating a wafer holding portion that holds the wafer.

[0003] Japanese Unexamined Patent Application Publication No. 2014-58038

[0004] The timing for completing grinding of the peripheral edge of a wafer is determined based on a predetermined grinding time. More specifically, grinding of the peripheral edge of the wafer is completed when a predetermined grinding time elapses from the start of grinding of the wafer. However, the thickness of the film formed on the peripheral edge of the wafer may vary from wafer to wafer. The grinding time for determining the grinding end point of the wafer is constant regardless of the wafer, so the film may remain on the peripheral edge of the wafer when the grinding time elapses. For this reason, the grinding time of the wafer is lengthened to prevent the film from remaining. However, when the grinding time is lengthened, not only throughput decreases, but also the wafer is excessively ground.

[0005] Accordingly, the present invention provides a grinding apparatus and a grinding method capable of accurately detecting a grinding end point of a wafer based on the state of the peripheral edge of the wafer.

[0006] In one embodiment, the wafer holding unit includes a holding stage for holding a wafer, a polishing head for polishing the wafer by pressing a polishing tool against the peripheral edge of the wafer on the holding stage, a stage rotation mechanism for rotating the holding stage around its axis, a high-frequency vibration device attached to the polishing head for applying high-frequency vibrations to the polishing head, a vibration sensor for detecting vibrations of the polishing head when the polishing tool is pressed against the peripheral edge of the wafer on the holding stage, and a vibration analysis unit for detecting the end point of wafer polishing based on the change in vibration of the polishing head detected by the vibration sensor, wherein the vibration analysis unit uses the vibration sensor to... A polishing apparatus is provided which extracts modulated high-frequency vibrations from a vibration detection signal indicating the vibration of the polishing head output by a filter, wherein the modulated high-frequency vibrations are vibrations having a frequency within a predetermined monitoring frequency range centered on the frequency of the high-frequency vibrations generated by the high-frequency vibration device, generates an envelope waveform by performing envelope processing on a modulated amplitude waveform showing the change in amplitude of the modulated high-frequency vibrations over time, generates an amplitude spectrum by performing a Fourier transform on the envelope waveform, and detects the polishing endpoint of the wafer based on the change in amplitude in the target frequency band of the amplitude spectrum.

[0007] In one embodiment, the frequency of the high-frequency vibration is higher than the frequency of vibration of the wafer holder and the stage rotation mechanism during operation. In one embodiment, the frequency of the high-frequency vibration is a frequency within the ultrasonic band. In one embodiment, the frequency of the high-frequency vibration is a frequency within the ultrasonic band from 20 kHz to 100 kHz. In one embodiment, the high-frequency vibration device is an ultrasonic transducer. In one embodiment, the vibration analysis unit is configured to determine the polishing endpoint at which the amplitude in the target frequency band changes across a threshold. In one embodiment, the vibration analysis unit is configured to determine the polishing endpoint at which the absolute value of the rate of change of the amplitude in the target frequency band falls below a threshold.

[0008] In one embodiment, a method is provided for polishing a wafer, in which a wafer is held, by rotating a holding stage of a wafer holding unit around its axis using a stage rotation mechanism, and polishing the wafer by pressing a polishing tool against the peripheral edge of the wafer on the holding stage with a polishing head, and while polishing the wafer, high-frequency vibration is applied to the polishing head with a high-frequency vibration device, and the vibration of the polishing head is detected by a vibration sensor, and a modulated high-frequency vibration is extracted by a filter from the vibration detection signal indicating the vibration of the polishing head output from the vibration sensor, the modulated high-frequency vibration is a vibration having a frequency within a predetermined monitoring frequency range centered on the frequency of the high-frequency vibration generated by the high-frequency vibration device, an envelope waveform is generated by performing envelope processing on the modulated amplitude waveform which shows the change in amplitude of the modulated high-frequency vibration over time, an amplitude spectrum is generated by performing a Fourier transform on the envelope waveform, and the polishing endpoint of the wafer is detected based on the change in amplitude over time in the target frequency band of the amplitude spectrum.

[0009] In one embodiment, the frequency of the high-frequency vibration is higher than the frequency of vibration of the wafer holder and the stage rotation mechanism during operation. In one embodiment, the frequency of the high-frequency vibration is a frequency within the ultrasonic band. In one embodiment, the frequency of the high-frequency vibration is a frequency within the ultrasonic band from 20 kHz to 100 kHz. In one embodiment, the high-frequency vibration device is an ultrasonic transducer. In one embodiment, detecting the end point of wafer polishing based on the time change of amplitude in the target frequency band means determining the end point of polishing where the amplitude in the target frequency band changes across a threshold. In one embodiment, detecting the end point of wafer polishing based on the time change of amplitude in the target frequency band means determining the end point of polishing where the absolute value of the rate of change of amplitude in the target frequency band falls below a threshold.

[0010] When the polishing head is polishing the periphery of the wafer, the high-frequency vibration device applies high-frequency vibration to the components of the polishing head, preferably components that directly reach the polishing area (e.g., the pressing component that presses the polishing tape). As a result, the amplitude of the high-frequency vibration is modulated by the vibration caused by the sliding contact between the wafer periphery and the polishing tool (hereinafter referred to as polishing vibration) and applied to the polishing head. In addition to the amplitude-modulated high-frequency vibration, the polishing head is also subjected to vibrations from the polishing apparatus itself (hereinafter referred to as mechanical vibration). Filtering, envelope processing, and Fourier transform processing extract the amplitude in the target frequency band that changes depending on the polishing vibration. The polishing vibration changes depending on the state of the film on the wafer periphery. For example, when the film is removed from the wafer periphery, the polishing vibration decreases or increases. Therefore, the polishing endpoint of the wafer periphery can be accurately determined based on the time change of the amplitude of the vibration in the target frequency band that exhibits the polishing vibration.

[0011] Figure 1A is an enlarged cross-sectional view showing the periphery of a wafer. Figure 1B is an enlarged cross-sectional view showing the periphery of a wafer. This is a side view showing one embodiment of a polishing apparatus for polishing the periphery of a wafer. This is a plan view showing one embodiment of a tilt mechanism. This is a graph showing an example of high-frequency vibration generated by a high-frequency vibration device. This is a graph showing an example of the time variation of modulated high-frequency vibration measured by the polishing head during polishing of the wafer periphery. This is a graph showing an example of a vibration spectrum showing the vibration of the polishing head detected by a vibration sensor during polishing of the wafer periphery. This is a graph showing an example of a modulated amplitude waveform showing the change in the amplitude of modulated high-frequency vibration within the monitoring frequency range with polishing time. This is a diagram illustrating one embodiment of Fourier transform processing performed on an envelope waveform. This is a graph showing an example of the time variation of amplitude in the target frequency band. This is a flowchart illustrating one embodiment of detecting the polishing endpoint of the wafer periphery. This is a cross-sectional view showing an example of a polishing tape.

[0012] Embodiments of the present invention will now be described with reference to the drawings. Figures 1A and 1B are enlarged cross-sectional views showing the peripheral edge of a wafer. More specifically, Figure 1A is a cross-sectional view of a so-called straight wafer, and Figure 1B is a cross-sectional view of a so-called round wafer. In this specification, the peripheral edge of the wafer W includes at least a bevel portion B. The peripheral edge of the wafer W may include the bevel portion B, a top edge portion E1, and a bottom edge portion E2.

[0013] The bevel portion B is the outermost surface of the wafer W that is inclined relative to the planar portion P, and has a chamfered or rounded shape. The planar portion P of the wafer W is usually the device surface on which the device is formed. In the wafer W of Figure 1A, the bevel portion B is the outermost surface of the wafer W, consisting of an upper inclined surface (upper bevel portion) S1, a lower inclined surface (lower bevel portion) S2, and a side portion (apex) R. In the wafer W of Figure 1B, the bevel portion B is the portion with a curved cross-section that constitutes the outermost surface of the wafer W.

[0014] The top edge portion E1 is an annular flat portion located radially inward of the bevel portion B and is situated within the device plane of the wafer W. The bottom edge portion E2 is an annular flat portion located on the opposite side of the top edge portion E1 and radially inward of the bevel portion B. The top edge portion E1 may also include the region where the device is formed.

[0015] Figure 2 is a side view showing one embodiment of a polishing apparatus for polishing the peripheral edge of a wafer W. In this embodiment, the polishing apparatus is configured to polish the peripheral edge of the wafer W by pressing a polishing tape 1, which serves as a polishing tool, against the peripheral edge of the wafer W with a polishing head 2. The polishing tape 1 has a polishing surface made of abrasive grains, and the peripheral edge of the wafer W is polished by the polishing surface of the polishing tape 1 sliding against the peripheral edge of the wafer W.

[0016] In other embodiments, polishing of the peripheral edge of the wafer W by the polishing apparatus may be performed by using a grinding wheel instead of the polishing tape 1 as the polishing tool, or by using a polishing pad (e.g., nonwoven fabric) as the polishing tool in the presence of a polishing liquid (slurry) (CMP treatment).

[0017] As shown in Figure 2, the polishing apparatus for polishing the peripheral edge of a wafer W comprises a wafer holding unit 3 having a holding stage 4 for holding the wafer W, a polishing head 2 positioned adjacent to the holding stage 4 and polishing the peripheral edge of the wafer W by pressing the polishing surface of the polishing tape 1 against the peripheral edge of the wafer W on the holding stage 4, and a stage rotation mechanism 6 for rotating the holding stage 4 around its axis.

[0018] The holding stage 4 is configured to hold a wafer W on its wafer holding surface 4a by vacuum suction. The wafer holding unit 3 includes the holding stage 4, a stage shaft 9 connected to the holding stage 4, and a bearing device 12 that rotatably supports the stage shaft 9. The stage shaft 9 is connected to a stage rotation mechanism 6. The stage rotation mechanism 6 and the bearing device 12 are fixed to a base 20. The stage rotation mechanism 6 is equipped with an electric motor and is configured to rotate the stage shaft 9 and the holding stage 4 together around the axis Cr of the holding stage 4.

[0019] The wafer W is placed on the wafer holding surface 4a of the holding stage 4 by a transport robot (not shown) such that the center O1 of the wafer W is on the axis Cr of the holding stage 4. The wafer W is held on the wafer holding surface 4a of the holding stage 4 with its device surface (the planar portion P in Figures 1A and 1B) facing upward. The stage rotation mechanism 6 rotates the wafer W around the axis Cr of the holding stage 4 (i.e., the axis of the wafer W).

[0020] The polishing apparatus further includes a polishing tape supply mechanism 24 that supplies polishing tape 1 to the polishing head 2 and retrieves the polishing tape 1 from the polishing head 2. The polishing tape supply mechanism 24 includes a tape unwinding reel 26 that supplies polishing tape 1 to the polishing head 2 and a tape taking reel 27 that retrieves the polishing tape 1 used for polishing the wafer W. Tension motors (not shown) are connected to the tape unwinding reel 26 and the tape taking reel 27, respectively. Each tension motor is capable of applying a predetermined torque to the tape unwinding reel 26 and the tape taking reel 27, thereby applying a predetermined tension to the polishing tape 1.

[0021] The polishing tape 1 is supplied to the polishing head 2 such that the polishing surface of the polishing tape 1 faces the peripheral edge of the wafer W. The polishing tape 1 is supplied to the polishing head 2 from the tape unwinding reel 26, and the polishing tape 1 used to polish the wafer W is collected on the tape take-up reel 27. The polishing tape supply mechanism 24 further includes a plurality of guide rollers 30, 31, 32, 33 for supporting the polishing tape 1. The direction of travel of the polishing tape 1 is guided by the guide rollers 30, 31, 32, 33.

[0022] The polishing head 2 includes a pressing member 38 that presses the polishing surface of the polishing tape 1 against the wafer W, and an air cylinder 39 that acts as an actuator to move the pressing member 38 toward the peripheral edge of the wafer W. The pressing force of the polishing tape 1 against the wafer W is adjusted by controlling the air pressure supplied to the air cylinder 39. The pressing member 38 is positioned on the back side of the polishing tape 1 (the side opposite to the polishing surface containing abrasive grains).

[0023] The polishing apparatus includes a lower supply nozzle 42 that supplies liquid to the lower surface of the wafer W, and an upper supply nozzle 43 that supplies liquid to the upper surface of the wafer W. An example of the liquid supplied to the wafer W is pure water. During the polishing of the wafer W, liquid is supplied to the lower surface of the wafer W from the lower supply nozzle 42, and liquid is supplied to the upper surface of the wafer W from the upper supply nozzle 43.

[0024] The polishing apparatus further includes a polishing head support member 46 that supports the polishing head 2, and a polishing head moving device 47 that moves the polishing head 2 and the polishing head support member 46 toward the holding stage 4 and toward the holding stage 4. The polishing head moving device 47 is attached to the base 20. When polishing the peripheral edge of the wafer W, the polishing head moving device 47 moves the polishing head 2 toward the peripheral edge of the wafer W on the holding stage 4. After polishing the peripheral edge of the wafer W is completed, the polishing head moving device 47 moves the polishing head 2 toward the peripheral edge of the wafer W on the holding stage 4.

[0025] The polishing apparatus further includes a tilt mechanism 56 as shown in Figure 3. Figure 3 is a plan view showing one embodiment of the tilt mechanism 56. As shown in Figure 3, the tilt mechanism 56 is configured to tilt the polishing head 2 relative to the wafer holding surface 4a of the holding stage 4. More specifically, the tilt mechanism 56 includes a crank arm 57 connected to the polishing head 2 and an arm rotation device 58 for rotating the crank arm 57. One end of the crank arm 57 is positioned at substantially the same height as the wafer holding surface 4a of the holding stage 4 and is connected to the arm rotation device 58. The other end of the crank arm 57 is connected to the polishing head 2. The arm rotation device 58 is fixed to the polishing head support member 46.

[0026] When the arm rotation device 58 rotates the crank arm 57, the entire polishing head 2 can be tilted relative to the wafer W on the wafer holding surface 4a of the holding stage 4. Furthermore, the tilt mechanism 56 is configured to maintain the polishing head 2 at a predetermined tilt angle. Therefore, the polishing head 2 can polish the peripheral edge of the wafer W while changing its tilt angle or while maintaining a predetermined tilt angle. Note that the specific configuration of the tilt mechanism 56 is not limited to the embodiment shown in Figure 3, as long as the polishing head 2 can be tilted relative to the wafer holding surface 4a of the holding stage 4 and the wafer W.

[0027] The polishing apparatus is electrically connected to an operation control unit 60 that controls the operation of each component of the polishing apparatus. The polishing head 2, stage rotation mechanism 6, polishing head moving device 47, polishing tape supply mechanism 24, and tilt mechanism 56 are electrically connected to the operation control unit 60. The operation of the polishing head 2, stage rotation mechanism 6, polishing head moving device 47, polishing tape supply mechanism 24, and tilt mechanism 56 is controlled by the operation control unit 60.

[0028] The operation control unit 60 comprises at least one computer. The operation control unit 60 comprises a storage device 60a and an arithmetic unit 60b. The arithmetic unit 60b includes a CPU (Central Processing Unit) or GPU (Graphics Processing Unit), etc., which performs calculations according to instructions contained in the program stored in the storage device 60a. The storage device 60a comprises a main memory (e.g., random access memory) accessible by the arithmetic unit 60b and an auxiliary storage device (e.g., a hard disk drive or solid-state drive) for storing data and programs. However, the specific configuration of the operation control unit 60 is not limited to these examples.

[0029] The peripheral edge of the wafer W is polished as follows: The upper supply nozzle 43 and the lower supply nozzle 42 supply liquid (e.g., pure water) to the upper and lower surfaces of the wafer W, while the stage rotation mechanism 6 rotates the holding stage 4 and the wafer W. The air cylinder 39 of the polishing head 2 moves the pressing member 38 toward the peripheral edge of the wafer W, and the pressing member 38 presses the polishing tape 1 against the peripheral edge of the wafer W. In this way, the polishing head 2 polishes the peripheral edge of the wafer W with the polishing tape 1. During polishing of the peripheral edge of the wafer W, the tilt mechanism 56 may gradually change the tilt angle of the polishing head 2 or maintain the polishing head 2 at a predetermined tilt angle.

[0030] As shown in Figure 2, the polishing apparatus further includes a high-frequency vibration device 63 attached to the pressing member 38 of the polishing head 2 and applying high-frequency vibration to the pressing member 38, a vibration sensor 65 that detects the vibration of the polishing head 2 when the polishing tape 1 is pressed against the peripheral edge of the wafer W on the holding stage, and a vibration analysis unit 70 that detects the polishing endpoint of the wafer W based on the change in vibration of the polishing head 2 generated by the vibration sensor 65.

[0031] The vibration sensor 65 is attached to the polishing head 2. An example of the vibration sensor 65 is an acceleration sensor. In this embodiment, the vibration sensor 65 is attached to the cover of the polishing head 2. In other embodiments, the vibration sensor 65 may be attached to the pressing member 38 or the air cylinder 39.

[0032] When the wafer holding unit 3 (including the holding stage 4, stage shaft 9, and bearing device 12) and the stage rotation mechanism 6 are operating, vibrations of the wafer holding unit 3 and the stage rotation mechanism 6 themselves (hereinafter referred to as mechanical vibrations) are transmitted to the polishing head 2. Furthermore, during polishing of the peripheral edge of the wafer W, vibrations caused by the sliding contact between the peripheral edge of the wafer W and the polishing tape 1 (hereinafter referred to as polishing vibrations) are also transmitted to the polishing head 2. Therefore, in addition to the high-frequency vibrations applied from the high-frequency vibration device 63, mechanical vibrations and polishing vibrations are applied to the polishing head 2. During polishing of the peripheral edge of the wafer W, the vibration sensor 65 detects vibrations of the polishing head 2, including high-frequency vibrations, mechanical vibrations, and polishing vibrations. The vibration sensor 65 is electrically connected to the vibration analysis unit 70, and vibration detection signals indicating vibrations of the polishing head 2 are transmitted from the vibration sensor 65 to the vibration analysis unit 70.

[0033] The vibration analysis unit 70 includes at least one computer. The vibration analysis unit 70 includes a storage device 70a and a computing device 70b. The computing device 70b includes a CPU (Central Processing Unit) or GPU (Graphics Processing Unit) that performs calculations according to instructions contained in the program stored in the storage device 70a. The storage device 70a includes a main memory (e.g., random access memory) accessible by the computing device 70b and an auxiliary storage device (e.g., a hard disk drive or solid-state drive) that stores data and programs. However, the specific configuration of the vibration analysis unit 70 is not limited to these examples.

[0034] Figure 4 is a graph showing an example of high-frequency vibration generated by the high-frequency vibration device 63. In the graph in Figure 4, the vertical axis represents the amplitude of the vibration, and the horizontal axis represents time. When the vibration sensor 65 is an acceleration sensor, the amplitude of the vibration is equal to the acceleration [m / s²]. ２ It may be expressed as ]. In this embodiment, the high-frequency vibration device 63 is configured to generate high-frequency vibrations having a frequency within the ultrasonic band. In one embodiment, the frequency of the high-frequency vibration is a frequency within the ultrasonic band from 20 kHz to 100 kHz. An example of the high-frequency vibration device 63 is an ultrasonic transducer. The vibration direction of the high-frequency vibration generated by the high-frequency vibration device 63 is parallel to the polishing surface of the polishing tape 1 that contacts the peripheral edge of the wafer W.

[0035] As shown in Figure 4, the high-frequency vibration device 63 generates high-frequency vibrations with a constant frequency. The frequency of the high-frequency vibrations is higher than the frequency of the mechanical vibrations during the operation of the wafer holding unit 3 (including the holding stage 4, stage shaft 9, and bearing device 12) and the stage rotation mechanism 6. Furthermore, the vibration velocity of the high-frequency vibrations is higher than the peripheral speed of the wafer W on the holding stage 4 rotated by the stage rotation mechanism 6. The peripheral speed of the wafer W is the tangential speed of the rotating wafer W. The vibration velocity [m / s] of the high-frequency vibrations is expressed by the following formula: Vibration velocity [m / s] = (2 × amplitude of vibration) / (period of vibration / 2)

[0036] Figure 5 is a graph showing an example of the time evolution of modulated high-frequency vibrations during polishing of the peripheral edge of the wafer W. As shown in Figure 5, the polishing vibrations (vibrations caused by the sliding contact between the peripheral edge of the wafer W and the polishing tape 1) modulate (vary) the amplitude of the high-frequency vibrations shown in Figure 4. This is because when the high-frequency vibrations generated by the high-frequency vibration device 63 (see Figure 4) are transmitted to the polishing tape 1, the amplitude of the high-frequency vibrations is modulated due to the state of the peripheral edge of the wafer W, and these modulated high-frequency vibrations are transmitted to the polishing head 2. On the other hand, mechanical vibrations transmitted to the polishing head 2 from the polishing head support member 46, etc., are transmitted to the polishing head 2 as is without modulating the high-frequency vibrations.

[0037] As shown in Figure 5, the amplitude of the high-frequency vibration fluctuates with polishing time. In other words, the change in the amplitude of the high-frequency vibration reflects the change in the polishing vibration. Therefore, the change in the polishing vibration can be monitored from the change in the amplitude of the high-frequency vibration. As long as the rotation speed of the wafer W remains constant during polishing, the mechanical vibration does not change substantially. In contrast, the polishing vibration changes depending on the state of the peripheral edge of the wafer W. For example, when the film is removed from the peripheral edge of the wafer W, the polishing vibration decreases or increases. Therefore, the change in the amplitude of the high-frequency vibration indicates a change in the polishing vibration, i.e., a change in the state of the peripheral edge of the wafer W.

[0038] Figure 6 is a graph showing an example of a vibration spectrum indicating the vibration of the polishing head 2 detected by the vibration sensor 65 during polishing of the peripheral edge of the wafer W. In Figure 6, the vertical axis represents the amplitude of the vibration, and the horizontal axis represents the frequency of the vibration. The vibration spectrum shows the relationship between multiple amplitudes included in the vibration detected by the vibration sensor 65 at a given time and the corresponding multiple frequencies. As shown in Figure 6, the vibration of the polishing head 2 includes mechanical vibration, polishing vibration, and modulated high-frequency vibration. The vibration spectrum shown in Figure 6 is generated from the vibration detection signal output from the vibration sensor 65.

[0039] As shown in Figure 6, the frequency band of polishing vibrations is typically within the frequency band of mechanical vibrations, and the mechanical vibrations are superimposed on the polishing vibrations. The mechanical vibrations act as noise to the polishing vibrations, making it difficult to determine the polishing endpoint at the periphery of the wafer W based on changes in the polishing vibrations.

[0040] Therefore, in this embodiment, the polishing endpoint of the peripheral edge of the wafer W is detected as follows. The high-frequency vibration device 63 applies high-frequency vibration to the pressing member 38 of the polishing head 2, and the polishing vibration modulates the amplitude of the high-frequency vibration. As a result, as shown in Figure 6, a high-frequency vibration with modulated amplitude, i.e., a modulated high-frequency vibration, appears. The modulated high-frequency vibration is a vibration generated by the modulation of the amplitude of the high-frequency vibration by the polishing vibration. The modulated high-frequency vibration includes a high-frequency vibration of frequency FH ​​applied to the pressing member 38 by the high-frequency vibration device 63 and a vibration with a frequency different from frequency FH. That is, as shown in Figure 6, the modulated high-frequency vibration includes a high-frequency vibration of frequency FH ​​and vibrations generated on both sides thereof.

[0041] The vibration analysis unit 70 is equipped with a filter 75 (see Figure 2). This filter 75 is configured to extract modulated high-frequency vibrations from the vibration detection signal indicating the vibration of the polishing head 2 output from the vibration sensor 65. The frequency of the modulated high-frequency vibrations includes a predetermined monitoring frequency range R1 centered on the frequency FH ​​of the high-frequency vibrations generated by the high-frequency vibration device 63. In one embodiment, as shown in Figure 6, the monitoring frequency range R1 is defined by the frequency FH ​​of the high-frequency vibrations ± the upper limit F2 of the target frequency band (described later) (FH - F2 to FH + F2). Since the frequency of the modulated high-frequency vibrations is higher than the frequencies of the mechanical vibrations and polishing vibrations, a high-pass filter or a band-pass filter is used as the filter 75.

[0042] FIG. 7 is a graph showing an example of a modulation amplitude waveform MW that illustrates a change in amplitude of modulated high-frequency vibration with polishing time within the monitoring frequency range R1. In one embodiment, the amplitude of the modulated high-frequency vibration within the monitoring frequency range R1 is obtained by converting the amplitude to an absolute value. As shown in FIG. 7, the vibration analysis unit 70 performs envelope processing on the modulation amplitude waveform MW to generate an envelope waveform EW. A publicly known technique can be applied to the envelope processing itself.

[0043] Next, as shown in FIG. 8, the vibration analysis unit 70 performs Fourier transform processing on the envelope waveform EW to generate an amplitude spectrum. A specific example of the Fourier transform processing is Fast Fourier Transform (FFT). The amplitude spectrum shows the relationship between the amplitude included in the envelope waveform EW and the corresponding frequency. The vibration analysis unit 70 detects the polishing end point of the peripheral edge of the wafer W based on the temporal change of the amplitude in the target frequency bands F1 to F2 of the amplitude spectrum. The target frequency bands F1 to F2 are a frequency range in which the amplitude changes along with a change in polishing vibration (that is, vibration caused by sliding contact between the polishing tape 1 and the peripheral edge of the wafer W), and is predetermined based on past polishing results, experiments, and the like.

[0044] FIG. 9 is a graph showing an example of a temporal change of the amplitude in the target frequency bands F1 to F2. In one embodiment, the amplitude in the target frequency bands F1 to F2 is a composite value calculated from the square root of the sum of squares of a plurality of amplitudes in the target frequency bands F1 to F2. In this example, the amplitude in the target frequency bands F1 to F2 decreases along with the polishing time. That is, as the film is removed from the peripheral edge of the wafer W by the polishing tape 1, the polishing vibration decreases. The vibration analysis unit 70 is configured to determine the polishing end point of the wafer W at a time point when the amplitude in the target frequency bands F1 to F2 changes across the threshold value. In the example shown in FIG. 9, the vibration analysis unit 70 determines the polishing end point when the amplitude in the target frequency bands F1 to F2 decreases below the threshold value.

[0045] Depending on the combination of the wafer W and the film material, as the film is removed from the peripheral edge of the wafer W by the polishing tape 1, polishing vibration may increase. Therefore, in this case, the vibration analysis unit 70 determines the polishing end point as the point in time when the amplitude in the target frequency band F1 to F2 increases beyond a threshold value.

[0046] When the film is completely removed from the peripheral edge of the wafer W by the polishing tape 1, the polishing vibration is expected to become constant. Therefore, in another embodiment, the vibration analysis unit 70 may be configured to calculate the rate of change of amplitude in the target frequency band F1 to F2, and determine the polishing end point when the absolute value of the rate of change of amplitude decreases below a predetermined threshold value.

[0047] FIG. 10 is a flowchart illustrating an embodiment of detecting a polishing end point at the peripheral edge of a wafer W. In step 101, the holding stage 4 is rotated by the stage rotation mechanism 6, and the wafer W on the holding stage 4 is rotated. In step 102, the polishing head 2 presses the polishing tape 1 against the peripheral edge of the wafer W on the holding stage 4 to polish the peripheral edge of the wafer W. In step 103, during polishing of the wafer W, while the high-frequency vibration device 63 applies high-frequency vibration to the pressing member 38 of the polishing head 2, the vibration sensor 65 detects the vibration of the polishing head 2.

[0048] In step 104, during polishing of the wafer W, the filter 75 extracts modulated high-frequency vibration (see FIG. 6) from the vibration detection signal output from the vibration sensor 65 that indicates the vibration of the polishing head 2. The frequency of the modulated high-frequency vibration includes a monitoring frequency range R1 (see FIG. 6) centered on the frequency FH of the high-frequency vibration generated by the high-frequency vibration device 63, and is higher than the frequency of mechanical vibration (vibration of the wafer holding unit 3 and the stage rotation mechanism 6 themselves) and polishing vibration (vibration caused by sliding contact between the peripheral edge of the wafer W and the polishing tape 1).

[0049] In step 105, the vibration analysis unit 70 performs envelope processing on the modulated amplitude waveform MW, which shows the change in amplitude of the modulated high-frequency vibration extracted by the filter 75 over time, to generate an envelope waveform EW (see Figure 7). In step 106, the vibration analysis unit 70 performs Fourier transform processing on the envelope waveform EW to generate an amplitude spectrum (see Figure 8). In step 107, the vibration analysis unit 70 detects the polishing endpoint of the peripheral edge of the wafer W based on the change in amplitude over time in the target frequency band F1 to F2 of the amplitude spectrum (see Figures 8 and 9).

[0050] The filter 75, envelope processing, and Fourier transform processing described above extract the amplitude in the target frequency band F1 to F2, which changes depending on the polishing vibration. The polishing vibration changes depending on the state of the film at the periphery of the wafer W. Therefore, the vibration analysis unit 70 can accurately determine the polishing endpoint at the periphery of the wafer W based on the time change of the vibration amplitude in the target frequency band F1 to F2, which reflects the polishing vibration.

[0051] The high-frequency vibrations applied to the pressing member 38 of the polishing head 2 from the high-frequency vibration device 63 contribute not only to detecting the polishing endpoint of the wafer W, but also to improving the polishing of the peripheral edge of the wafer W. In other words, the pressing member 38 to which high-frequency vibrations are applied improves the polishing rate of the peripheral edge of the wafer W, allowing the polishing tape 1 to polish the peripheral edge of the wafer W smoothly.

[0052] Figure 11 is a cross-sectional view showing an example of a polishing tape 1. As shown in Figure 11, the polishing tape 1 has a plurality of abrasive grains 100, a resin binder 102 that holds these abrasive grains 100, and a base tape 105 coated with the resin binder 102. The polishing surface of the polishing tape 1 is composed of a plurality of abrasive grains 100 exposed on the resin binder 102. However, since the plurality of abrasive grains 100 that make up the polishing surface are unevenly distributed, it is difficult for the polishing surface of the polishing tape 1 to uniformly polish the peripheral edge of the wafer W.

[0053] In this embodiment, the high-frequency vibration device 63 vibrates the polishing tape 1, so that the multiple abrasive grains 100 constituting the polishing surface are uniformly slid into contact with the peripheral edge of the wafer W. As a result, the polishing tape 1 can smoothly polish the peripheral edge of the wafer W.

[0054] The embodiments described above are intended to enable persons with ordinary skill in the art to implement the present invention. Various modifications of the above embodiments can be made naturally by those skilled in the art, and the technical idea of ​​the present invention can be applied to other embodiments as well. Therefore, the present invention is not limited to the embodiments described, but is to be interpreted in the broadest sense according to the technical idea defined by the claims.

[0055] The present invention can be used in techniques for polishing wafers by pressing a polishing tool against a rotating wafer, and in particular in techniques for detecting the end point of wafer polishing.

[0056] W Wafer 1 Polishing tape 2 Polishing head 3 Wafer holder 4 Holding stage 4a Wafer holding surface 6 Stage rotation mechanism 9 Stage shaft 12 Bearing device 20 Base 24 Polishing tape supply mechanism 26 Tape unwinding reel 27 Tape winding reel 30, 31, 32, 33 Guide roller 38 Pressing member 39 Air cylinder 42 Lower supply nozzle 43 Upper supply nozzle 46 Polishing head support member 47 Polishing head moving device 56 Tilt mechanism 57 Crank arm 58 Arm rotation device 63 High-frequency vibration device 65 Vibration sensor 70 Vibration analysis unit 75 Filter

Claims

1. A wafer holding unit having a holding stage for holding a wafer; a polishing head for polishing the wafer by pressing a polishing tool against the peripheral edge of the wafer on the holding stage; a stage rotation mechanism for rotating the holding stage about its axis; a high-frequency vibration device attached to the polishing head for applying high-frequency vibration to the polishing head; a vibration sensor for detecting the vibration of the polishing head when the polishing tool is pressed against the peripheral edge of the wafer on the holding stage; and a vibration analysis unit for detecting the end point of wafer polishing based on the change in vibration of the polishing head detected by the vibration sensor, wherein the vibration analysis unit extracts modulated high-frequency vibration from a vibration detection signal indicating the vibration of the polishing head output from the vibration sensor using a filter, the modulated high-frequency vibration being a vibration having a frequency within a predetermined monitoring frequency range centered on the frequency of the high-frequency vibration generated by the high-frequency vibration device, generates an envelope waveform by performing envelope processing on a modulated amplitude waveform showing the change in amplitude of the modulated high-frequency vibration over time, and generates an amplitude spectrum by performing a Fourier transform on the envelope waveform. A polishing apparatus configured to detect the polishing endpoint of the wafer based on the time variation of the amplitude in the target frequency band of the amplitude spectrum.

2. The polishing apparatus according to claim 1, wherein the frequency of the high-frequency vibration is higher than the frequency of vibration of the wafer holding part and the stage rotation mechanism during operation.

3. The polishing apparatus according to claim 1, wherein the frequency of the high-frequency vibration is a frequency within the ultrasonic band.

4. The polishing apparatus according to claim 3, wherein the frequency of the high-frequency vibration is a frequency within the ultrasonic band from 20 kHz to 100 kHz.

5. The polishing apparatus according to claim 3, wherein the high-frequency vibration device is an ultrasonic transducer.

6. The polishing apparatus according to claim 1, wherein the vibration analysis unit is configured to determine the polishing endpoint where the amplitude in the target frequency band changes across a threshold.

7. The polishing apparatus according to claim 1, wherein the vibration analysis unit is configured to determine the polishing endpoint at which the absolute value of the rate of change of amplitude in the target frequency band falls below a threshold.

8. A polishing method comprising: rotating a holding stage of a wafer holding unit that holds a wafer around its axis using a stage rotation mechanism; polishing the wafer by pressing a polishing tool against the peripheral edge of the wafer on the holding stage with a polishing head; applying high-frequency vibration to the polishing head with a high-frequency vibration device while polishing the wafer, detecting the vibration of the polishing head with a vibration sensor; extracting a modulated high-frequency vibration from the vibration detection signal indicating the vibration of the polishing head output from the vibration sensor using a filter, wherein the modulated high-frequency vibration is a vibration having a frequency within a predetermined monitoring frequency range centered on the frequency of the high-frequency vibration generated by the high-frequency vibration device; generating an envelope waveform by performing envelope processing on a modulated amplitude waveform showing the change in amplitude of the modulated high-frequency vibration over time; generating an amplitude spectrum by performing a Fourier transform on the envelope waveform; and detecting the polishing endpoint of the wafer based on the change in amplitude in the target frequency band of the amplitude spectrum.

9. The polishing method according to claim 8, wherein the frequency of the high-frequency vibration is higher than the frequency of vibration of the wafer holding part and the stage rotation mechanism during operation.

10. The polishing method according to claim 8, wherein the frequency of the high-frequency vibration is a frequency within the ultrasonic band.

11. The polishing method according to claim 10, wherein the frequency of the high-frequency vibration is a frequency within the ultrasonic band from 20 kHz to 100 kHz.

12. The polishing method according to claim 10, wherein the high-frequency vibration device is an ultrasonic transducer.

13. The polishing method according to claim 8, wherein detecting the polishing endpoint of the wafer based on the time change of the amplitude in the target frequency band means determining the polishing endpoint where the amplitude in the target frequency band changes across a threshold.

14. The polishing method according to claim 8, wherein detecting the polishing endpoint of the wafer based on the time change of amplitude in the target frequency band means determining the polishing endpoint at which the absolute value of the rate of change of amplitude in the target frequency band falls below a threshold.

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