Polishing apparatus and polishing method

Abstract

The present invention relates to a technology of polishing a wafer by pressing a polishing tool against the wafer during rotation. A polishing apparatus comprises: a holding stage (4) that holds a wafer (W); a polishing head (2) that is disposed adjacent to the holding stage (4) and polishes a wafer (W) by pressing a polishing tool (1) against the wafer (W) on the holding stage (4); a stage rotation mechanism (6) that rotates the holding stage (4) about the axial center thereof; a vibration sensor (65) that detects vibration of the holding stage (4) while the holding stage (4) is in rotation; and a vibration analysis unit (70) that detects an abnormality on the basis of a vibration signal indicating the vibration outputted from the vibration sensor (65).

Description

Polishing Apparatus and Polishing Method

[0001] The present invention relates to a technique for polishing a wafer by pressing a polishing tool against a rotating wafer.

[0002] In the manufacturing process of semiconductor devices, various materials are deposited on a wafer. As a result, an unnecessary film is 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, polishing of the peripheral edge of the wafer by a polishing apparatus is performed. This type of polishing apparatus polishes the peripheral edge of the wafer by pressing polishing tape against the peripheral edge of the wafer while rotating a holding stage that holds the wafer.

[0003] Japanese Unexamined Patent Publication No. 2023-63830

[0004] However, the center of the wafer may not coincide with the rotation center of the holding stage due to various causes such as defects in the assembly of the polishing apparatus, defects in the wafer transfer robot, and the surface condition of the holding stage. If the center of the wafer deviates from the rotation center of the holding stage beyond an allowable level, the polishing tape cannot uniformly polish the peripheral edge of the wafer. Furthermore, portions of the wafer that should not be polished may be polished by the polishing tape.

[0005] Accordingly, the present invention provides a polishing apparatus and a polishing method capable of detecting an abnormality such as eccentricity of a wafer with respect to a holding stage.

[0006] In one aspect, there is provided a polishing apparatus including: a holding stage that holds a wafer; a polishing head disposed adjacent to the holding stage, the polishing head polishing the wafer by pressing a polishing tool against the wafer on the holding stage; a stage rotation mechanism that rotates the holding stage about its axis; a vibration sensor that detects vibration of the holding stage while the holding stage is rotating; and a vibration analysis unit that detects an abnormality based on a vibration signal indicating the vibration output from the vibration sensor.

[0007] In one embodiment, a polishing method is provided in which a holding stage that holds a wafer is rotated about its axis by a stage rotation mechanism, a polishing tool is pressed against the wafer on the holding stage by a polishing head to polish the wafer, vibrations of the holding stage while the holding stage is rotating are detected by a vibration sensor, and an abnormality is detected based on the vibration signal indicating the vibration output from the vibration sensor.

[0008] The vibrations associated with the rotation of the holding stage change due to factors such as wafer eccentricity relative to the holding stage and malfunctions in the polishing apparatus itself. Therefore, various abnormalities can be detected based on the changes in vibration. Furthermore, as the wafer is polished, the wafer's film is removed and its underlying layer (e.g., the silicon layer) is exposed. As a result, the vibrations of the holding stage and the polishing head change. Therefore, the end point of wafer polishing can be detected based on the changes in vibration.

[0009] 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 polishing head vibration when the center of the wafer is located within an allowable level from the axis of the holding stage. This is a graph showing an example of polishing head vibration when the center of the wafer is located beyond an allowable level from the axis of the holding stage. This is a graph showing an example of vibration spectrum when there is a malfunction in the stage rotation mechanism. This is a graph showing the change in vibration intensity for each frequency with respect to polishing time from the start of polishing the periphery of the wafer to the detection of the polishing end point. This is a graph showing the change in vibration intensity for each frequency with respect to polishing time from the start of polishing the periphery of the wafer to the detection of the polishing end point. This is a diagram showing one embodiment in which a vibration sensor is attached to the tilt mechanism. This is a diagram showing one embodiment in which a vibration sensor is attached to a bearing device.

[0010] 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.

[0011] 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.

[0012] 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.

[0013] 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 is used as a polishing tool, against the peripheral edge of the wafer W with a polishing head 2. 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 a polishing tool, or by using a polishing pad (e.g., nonwoven fabric) as a polishing tool in the presence of a polishing liquid (slurry) (CMP treatment). In yet another embodiment, the polishing apparatus may be configured to polish the wafer W by pressing a polishing tool such as a polishing tape against a part of the wafer W other than the peripheral edge (e.g., the top surface of the wafer W).

[0014] As shown in Figure 2, the polishing apparatus for polishing the peripheral edge of a wafer W comprises 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 a 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.

[0015] The holding stage 4 is configured to hold a wafer W on its wafer holding surface 4a by vacuum suction. The holding stage 4 is connected to a stage shaft 9, which is connected to a stage rotation mechanism 6. The stage shaft 9 is rotatably supported by a bearing device 12. The stage rotation mechanism 6 and the bearing device 12 are fixed to a base 20. The stage rotation mechanism 6 includes 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.

[0016] 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 flat part P in Figure 1) 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).

[0017] 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 applies 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.

[0018] 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.

[0019] 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).

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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 Module), etc., which performs calculations according to instructions contained in the program stored in the storage device 60a. The storage device 60a comprises main memory (e.g., random access memory) accessible by the arithmetic unit 60b and auxiliary storage (e.g., 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.

[0026] 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.

[0027] As shown in Figure 2, the polishing apparatus further includes a vibration sensor 65 that detects vibrations of the holding stage 4 when the holding stage 4 is rotating, and a vibration analysis unit 70 that detects abnormalities based on the vibration signal output from the vibration sensor 65. The vibration signal is a signal indicating vibration detected by the vibration sensor 65.

[0028] In this embodiment, the vibration sensor 65 is attached to the polishing head 2. The vibration of the rotating holding stage 4 is transmitted to the polishing head 2 via the stage shaft 9, stage rotation mechanism 6, polishing head moving device 47, polishing head support member 46, and tilt mechanism 56. During polishing of the peripheral edge of the wafer W, the vibration of the rotating holding stage 4 is transmitted to the polishing head 2 via the wafer W. Therefore, the vibration sensor 65 attached to the polishing head 2 can detect the vibration of the holding stage 4. The vibration sensor 65 is electrically connected to the vibration analysis unit 70, and the vibration signal indicating the vibration of the holding stage 4 is transmitted from the vibration sensor 65 to the vibration analysis unit 70.

[0029] 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 Module) 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.

[0030] If there is any abnormality in the operation of the polishing apparatus, or if there is a malfunction in the polishing apparatus itself, a change in the vibration of the rotating holding stage 4 will be observed. For example, if the center O1 of the wafer W is more than an acceptable distance from the axis Cr of the holding stage 4, the holding stage 4, the wafer W, and the polishing head 2 polishing the wafer W will vibrate significantly while the holding stage 4 and the wafer W are rotating.

[0031] Figure 4 is a graph showing an example of vibration of the polishing head 2 when the center O1 of the wafer W is located within an acceptable level from the axis Cr of the holding stage 4, and Figure 5 is a graph showing an example of vibration of the polishing head 2 when the center O1 of the wafer W is located beyond an acceptable level from the axis Cr of the holding stage 4. In Figures 4 and 5, the vertical axis represents the intensity of vibration, and the horizontal axis represents the polishing time. The intensity of vibration is expressed as the acceleration of the object [m / s²]. ２ It is represented by ].

[0032] The vibration graphs shown in Figures 4 and 5 were generated by the vibration analysis unit 70 from vibration signals output from a vibration sensor 65 attached to the polishing head 2 shown in Figure 2. When the holding stage 4 rotates together with the wafer W, the intensity of vibration within a predetermined eccentricity monitoring frequency range fluctuates at a frequency corresponding to the rotation speed of the wafer W and the holding stage 4 (hereinafter referred to as the rotation frequency). The vibration sensor 65 measures the intensity of vibration at the rotation frequency.

[0033] When the center O1 of the wafer W is located within an acceptable level from the axis Cr of the holding stage 4, the vibration intensity at the rotation frequency is less than the eccentricity threshold TH1, as shown in Figure 4. In contrast, as shown in Figure 5, when the center O1 of the wafer W is located beyond an acceptable level from the axis Cr of the holding stage 4, the vibration intensity at the rotation frequency within the eccentricity monitoring frequency range exceeds the eccentricity threshold TH1. In one embodiment, the vibration analysis unit 70 is configured to monitor the vibration intensity within the eccentricity monitoring frequency range when the holding stage 4 and the wafer W are rotating, and to generate an eccentricity alarm signal indicating that the wafer W is eccentric with respect to the holding stage 4 when the vibration intensity within the eccentricity monitoring frequency range exceeds the eccentricity threshold TH1.

[0034] The eccentricity monitoring frequency range is a range of vibration frequencies in which the intensity of vibration tends to change due to the eccentricity of the wafer W relative to the holding stage 4, and is predetermined from experiments, past wafer polishing, etc. In one embodiment, the vibration intensity within the eccentricity monitoring frequency range is the maximum, minimum, or average value of the vibration intensity within the eccentricity monitoring frequency range, or the vibration intensity at a selected frequency within the eccentricity monitoring frequency range.

[0035] The vibration analysis unit 70 may compare the intensity of vibrations within the eccentricity monitoring frequency range with the eccentricity threshold TH1 during polishing of the peripheral edge of the wafer W, or it may compare the intensity of vibrations within the eccentricity monitoring frequency range with the eccentricity threshold TH1 after the rotation of the holding stage 4 and the wafer W has started, but before polishing of the peripheral edge of the wafer W has started. In this embodiment, since the vibration sensor 65 is attached to the polishing head 2, vibrations from the holding stage 4 are easily transmitted to the polishing head 2 during polishing of the peripheral edge of the wafer W. Therefore, in this embodiment, the vibration analysis unit 70 compares the intensity of vibrations within the eccentricity monitoring frequency range with the eccentricity threshold TH1 during polishing of the peripheral edge of the wafer W.

[0036] However, even before polishing the peripheral edge of the wafer W (before the polishing tape 1 contacts the peripheral edge of the wafer W), vibrations of the rotating holding stage 4 are transmitted to the polishing head 2 via the stage shaft 9, stage rotation mechanism 6, polishing head moving device 47, polishing head support member 46, and tilt mechanism 56. Therefore, in one embodiment, the vibration analysis unit 70 may compare the intensity of vibrations within the eccentricity monitoring frequency range with the eccentricity threshold TH1 before polishing the peripheral edge of the wafer W and while the holding stage 4 and wafer W are rotating.

[0037] When the center O1 of the wafer W is separated from the axis Cr of the holding stage 4 by more than an acceptable level, the holding stage 4 and the polishing head 2 vibrate significantly. As a result, as shown in Figure 5, the vibration intensity exceeds the eccentricity threshold TH1. The vibration analysis unit 70 generates an eccentricity alarm signal indicating that the wafer W is eccentric with respect to the holding stage 4, sends the eccentricity alarm signal to a display device (not shown), and causes the display device to display an eccentricity alarm indicating the eccentricity of the wafer W with respect to the holding stage 4. Furthermore, the vibration analysis unit 70 may send an eccentricity alarm signal to the operation control unit 60, and the operation control unit 60 may give commands to each component of the polishing apparatus to stop polishing the peripheral edge of the wafer W.

[0038] Eccentricity of the wafer W relative to the holding stage 4 can occur due to several causes. For example, these causes include malfunctions in the transport robot that transports the wafer W to the holding stage 4, and malfunctions in the assembly of the polishing equipment. By recognizing the eccentricity alarm displayed on the display device, the operator can recognize the need for repairs to the transport robot or polishing equipment.

[0039] Changes in the vibration of the rotating holding stage 4 can also be caused by factors other than eccentricity of the wafer W relative to the holding stage 4. For example, when the rotational speed of the holding stage 4 and the wafer W is significantly lower than the set rotational speed specified in the polishing recipe, the vibration of the holding stage 4 and the wafer W decreases. Therefore, the vibration analysis unit 70 can detect malfunctions of the stage rotation mechanism 6 based on changes in the vibration of the rotating holding stage 4.

[0040] In one embodiment, the vibration analysis unit 70 is configured to generate a vibration spectrum from the vibration signal, which shows the relationship between vibration intensity and vibration frequency. The vibration spectrum represents the vibration intensity at each frequency. Figure 6 is a graph showing an example of a vibration spectrum when there is a malfunction in the stage rotation mechanism 6. As shown in Figure 6, the vibration analysis unit 70 is configured to generate a rotation alarm signal indicating a malfunction in the stage rotation mechanism 6 when the vibration intensity within a predetermined rotation monitoring frequency range R2 is lower than the rotation threshold TH2. The predetermined rotation monitoring frequency range R2 is a range of vibration frequencies in which the vibration intensity tends to change according to changes in the rotation speed of the holding stage 4, and is predetermined from experiments, past wafer polishing, etc. In one embodiment, the vibration intensity within the rotation monitoring frequency range R2 is the maximum value, minimum value, or average of the vibration intensity within the rotation monitoring frequency range R2, or the vibration intensity at a selected frequency within the rotation monitoring frequency range R2.

[0041] The solid line graph in Figure 6 represents the vibration spectrum when the holding stage 4 and wafer W are rotating at the set rotational speed specified in the polishing recipe, while the dotted line graph in Figure 6 represents the vibration spectrum when the holding stage 4 and wafer W are rotating at a rotational speed lower than the set rotational speed. In the example shown in Figure 6, the eccentricity of the wafer W relative to the holding stage 4 is within the acceptable range (i.e., the intensity of vibration within the eccentricity monitoring frequency range is lower than the eccentricity threshold TH1).

[0042] As shown in Figure 6, when the current rotational speed of the holding stage 4 and wafer W is lower than the set rotational speed, the vibration intensity within the rotational monitoring frequency range R2 decreases. When the current rotational speed of the holding stage 4 is too low, it is assumed that a malfunction of the stage rotation mechanism 6 is occurring. Therefore, the vibration analysis unit 70 monitors the vibration intensity within a predetermined rotational monitoring frequency range R2, and when the vibration intensity within the predetermined rotational monitoring frequency range R2 is lower than the rotational threshold TH2, it generates a rotational alarm signal indicating a malfunction of the stage rotation mechanism 6.

[0043] Furthermore, the vibration analysis unit 70 sends a rotation alarm signal to a display device (not shown), causing the display device to show a rotation alarm indicating a malfunction of the stage rotation mechanism 6. The vibration analysis unit 70 may also send a rotation alarm signal to the operation control unit 60, which may then issue a command to the stage rotation mechanism 6 to stop the rotation of the holding stage 4. By recognizing the rotation alarm displayed on the display device, the worker can recognize the need to repair the stage rotation mechanism 6.

[0044] The vibration analysis unit 70 may compare the intensity of vibration within the rotation monitoring frequency range R2 with the rotation threshold TH2 during polishing of the peripheral edge of the wafer W, or alternatively, may compare the intensity of vibration within the rotation monitoring frequency range R2 with the rotation threshold TH2 after the rotation of the holding stage 4 and the wafer W is started and before the polishing of the peripheral edge of the wafer W is started. In the present embodiment, since the vibration sensor 65 is attached to the polishing head 2, the vibration of the holding stage 4 is easily transmitted to the polishing head 2 during polishing of the peripheral edge of the wafer W. Therefore, in the present embodiment, the vibration analysis unit 70 compares the intensity of vibration within the rotation monitoring frequency range R2 with the rotation threshold TH2 during polishing of the peripheral edge of the wafer W.

[0045] However, even before polishing the peripheral edge of the wafer W (before the polishing tape 1 contacts the peripheral edge of the wafer W), the vibration of the rotating holding stage 4 is transmitted to the polishing head 2 via the stage shaft 9, the stage rotation mechanism 6, the polishing head moving device 47, the polishing head support member 46, and the tilt mechanism 56. Therefore, in one embodiment, the vibration analysis unit 70 may compare the intensity of vibration within the rotation monitoring frequency range R2 with the rotation threshold TH2 before polishing the peripheral edge of the wafer W and during rotation of the holding stage 4 and the wafer W.

[0046] The rotation threshold TH2 described above can vary according to the set rotation speed of the holding stage 4. Specifically, the higher the set rotation speed of the holding stage 4 is, the higher the rotation threshold TH2 is. Therefore, in one embodiment, a plurality of rotation thresholds respectively corresponding to different set rotation speeds of the holding stage 4 are stored in advance in the storage device of the vibration analysis unit 70. The vibration analysis unit 70 is configured to select the rotation threshold corresponding to the current set rotation speed of the holding stage 4 from the plurality of rotation thresholds.

[0047] The rotation monitoring frequency range R2 is a frequency range of vibration in which the vibration intensity tends to change in accordance with a change in the rotation speed of the holding stage 4. Therefore, the rotation monitoring frequency range R2 can vary depending on the set rotation speed of the holding stage 4. Therefore, in one embodiment, a plurality of rotation monitoring frequency ranges respectively corresponding to different set rotation speeds of the holding stage 4 are stored in advance in a storage device of the vibration analysis unit 70. The vibration analysis unit 70 is configured to select the rotation monitoring frequency range corresponding to the current set rotation speed of the holding stage 4 from the plurality of rotation monitoring frequency ranges.

[0048] Next, an embodiment for detecting an operation failure of the polishing head 2 based on vibration of the rotating holding stage 4 will be described. In the embodiment described below, the vibration analysis unit 70 is configured to detect a failure of the polishing head 2 based on a vibration signal indicating vibration output from the vibration sensor 65. More specifically, the vibration analysis unit 70 is configured to determine a peak value of vibration intensity of the holding stage 4 during a predetermined polishing start period, and generate a polishing head alarm signal indicating an operation failure of the polishing head 2 when the peak value is smaller than a polishing start threshold value.

[0049] FIG. 7 is a graph showing a change in vibration intensity for each frequency with polishing time from the start of polishing of the peripheral edge of a wafer W to detection of a polishing end point. In FIG. 7, frequencies F1, F2, F3, F4, and F5 represent different vibration frequencies. The polishing start period TP1 includes a time point when polishing of the peripheral edge of the wafer W is started. The polishing start period TP1 shown in FIG. 7 includes a start command time point SP at which the operation control unit 60 instructs the polishing head 2 to press the polishing tape 1 against the peripheral edge of the wafer W. In one example, the predetermined polishing start period TP1 is from a time point several seconds before the start command time point SP to a time point several seconds after the start command time point SP.

[0050] When the polishing tape 1 comes into contact with the peripheral edge of the wafer W on the rotating holding stage 4, the intensity of vibration of the holding stage 4 temporarily increases. In particular, in this embodiment, since the vibration sensor 65 is attached to the polishing head 2 as shown in Figure 2, the polishing head 2 is prone to vibrating significantly when the polishing tape 1 comes into contact with the peripheral edge of the wafer W. If there is a malfunction in the air cylinder 39 (see Figure 2) acting as an actuator for the polishing head 2, or a malfunction in the system that supplies gas to the air cylinder 39, the polishing head 2 will not be able to bring the polishing tape 1 into contact with the peripheral edge of the wafer W with the set force. As a result, the intensity of vibration of the holding stage 4 and the polishing head 2 during the polishing start period TP1 will not reach the expected level.

[0051] Therefore, the vibration analysis unit 70 is configured to determine the peak value of the vibration intensity during the polishing start period TP1, and to generate a polishing head alarm signal indicating a malfunction of the polishing head 2 when the peak value is smaller than the polishing start threshold TH3. In one embodiment, during the polishing start period TP1, if the peak value PK1 of the vibration intensity at a pre-selected frequency (for example, frequency F1) is smaller than the polishing start threshold TH3, the vibration analysis unit 70 generates a polishing head alarm signal indicating a malfunction of the polishing head 2.

[0052] The vibration analysis unit 70 sends a polishing head alarm signal to a display device (not shown), causing the display device to show a polishing head alarm indicating a malfunction of the polishing head 2. Furthermore, the vibration analysis unit 70 may send a polishing head alarm signal to the operation control unit 60, which may then stop the operation of the polishing head 2. By recognizing the polishing head alarm displayed on the display device, the worker can recognize the need to repair the polishing head 2 or related equipment.

[0053] The embodiments described so far relate to a technique for detecting malfunctions of the polishing apparatus based on the vibration of the holding stage 4. However, the embodiments described below relate to a technique for detecting the polishing endpoint of the peripheral edge of the wafer W based on the vibration of the holding stage 4. As the peripheral edge of the wafer W progresses and the film is removed from the peripheral edge, the underlying layer beneath the film is exposed. Since the coefficient of friction between the polishing tape 1 and the film is different from the coefficient of friction between the polishing tape 1 and the underlying layer, the vibrations of the wafer W, the holding stage 4, and the polishing head 2 change.

[0054] Therefore, in the embodiment described below, the vibration analysis unit 70 is configured to detect the polishing endpoint of the peripheral edge of the wafer W based on a vibration signal indicating vibration output from the vibration sensor 65. More specifically, the vibration analysis unit 70 is configured to determine the peak value of the vibration intensity within a predetermined endpoint monitoring frequency range during a predetermined polishing final period TP2 shown in Figure 7, and to generate a polishing endpoint detection signal indicating the polishing endpoint of the peripheral edge of the wafer W when the peak value is greater than the polishing endpoint threshold TH4.

[0055] The final polishing period TP2 includes the predicted polishing endpoint EP, which is predetermined based on experiments or past wafer polishing. In one example, a predetermined final polishing period TP2 is from a few seconds before the predicted polishing endpoint EP to a few seconds after the predicted polishing endpoint EP.

[0056] The endpoint monitoring frequency range is a range of vibration frequencies in which the intensity of vibration tends to change at the end point of polishing the peripheral edge of the wafer W, and is predetermined based on experiments, past wafer polishing data, etc. In one embodiment, the vibration intensity within the endpoint monitoring frequency range is the maximum, minimum, or average value of the vibration intensity within the endpoint monitoring frequency range, or the vibration intensity at a selected frequency within the endpoint monitoring frequency range.

[0057] The vibration analysis unit 70 is configured to determine the peak value of the vibration intensity during the final polishing period TP2, and to generate a polishing endpoint detection signal indicating the polishing endpoint of the peripheral edge of the wafer W when the peak value of the vibration intensity is greater than the polishing endpoint threshold TH4. In one embodiment, during the final polishing period TP2, when the peak value PE1 of the vibration intensity at a pre-selected frequency (for example, frequency F1) is greater than the polishing endpoint threshold TH4, the vibration analysis unit 70 generates a polishing endpoint detection signal indicating the polishing endpoint of the peripheral edge of the wafer W.

[0058] The vibration analysis unit 70 sends a polishing endpoint detection signal to the operation control unit 60, and the operation control unit 60 gives commands to each component of the polishing apparatus to stop polishing the peripheral edge of the wafer W. In this way, according to this embodiment, the polishing endpoint of the peripheral edge of the wafer W can be detected based on the change in vibration of the holding stage 4 and the polishing head 2.

[0059] As shown in Figure 8, depending on the structure of the wafer W's periphery, the vibration intensity of the holding stage 4 and polishing head 2 may decrease when the polishing of the wafer W's periphery ends. Therefore, in one embodiment, the vibration analysis unit 70 is configured to determine the bottom value VE1 of the vibration intensity within a predetermined endpoint monitoring frequency range during a predetermined final polishing period TP2, and to generate a polishing endpoint detection signal indicating the polishing endpoint of the wafer W's periphery when the bottom value VE1 is smaller than the polishing endpoint threshold TH4. Even in this case, the polishing endpoint of the wafer W's periphery can be detected based on the change in vibration of the holding stage 4 and polishing head 2.

[0060] In the embodiments described with reference to Figures 2 to 8, the vibration sensor 65 is attached to the polishing head 2. However, in other embodiments, as shown in Figure 9, the vibration sensor 65 may be attached to a tilt mechanism 56 that tilts the polishing head 2. The vibration sensor 65 may be attached to the crank arm 57 or arm rotating device 58 of the tilt mechanism 56. In yet another embodiment, as shown in Figure 10, the vibration sensor 65 may be attached to a bearing device 12. In the embodiments shown in Figures 9 and 10, the vibration sensor 65 can perform the same function as the vibration sensor 65 in the embodiments described with reference to Figures 2 to 8.

[0061] Acoustic emission sensors and ultrasonic sensors are sometimes used to detect abnormalities in machinery. However, vibration sensors 65 have the following advantages over acoustic and ultrasonic sensors.

[0062] The vibrations generated from the holding stage 4 or polishing head 2 during wafer polishing are mainly in the frequency range of 20 kHz or less, lower than ultrasonic or acoustic emission. The vibration sensor 65 is suitable for detecting such low-frequency vibrations. In addition, even if the vibration sensor 65 is placed at a distance from the vibration source, the vibration is transmitted to the vibration sensor 65 through each component of the polishing apparatus, so the vibration sensor 65 can detect vibrations with high sensitivity. In contrast, acoustic sensors that detect elastic waves have difficulty detecting elastic waves if the distance between the elastic wave source and the acoustic sensor is large. Also, if there is a joint between the elastic wave source and the acoustic sensor, the elastic wave is greatly attenuated, and the acoustic sensor cannot detect the elastic wave with high sensitivity.

[0063] Ultrasonic sensors are susceptible to noise in the surrounding environment of the object being detected. In particular, polishing equipment generates vibrations (noise) across a wide frequency range from its rotating mechanism and sliding members, making it difficult for ultrasonic sensors to detect the necessary signals due to the influence of this noise. Furthermore, while acoustic and ultrasonic sensors have the characteristic of having high detection sensitivity only in specific frequency bands, the vibration sensor 65 has the characteristic of having flat detection sensitivity over a wide frequency band. In addition, since the frequency range that can be detected by the vibration sensor 65 coincides with the range of audible sound, vibration detection by the vibration sensor 65 can be associated with the generation of abnormal noise from the polishing equipment.

[0064] 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.

[0065] This invention can be used in techniques for polishing wafers by pressing a polishing tool against a rotating wafer.

[0066] W Wafer 1 Polishing tape 2 Polishing head 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 65 Vibration sensor 70 Vibration analysis unit

Claims

1. A polishing apparatus comprising: a holding stage for holding a wafer; a polishing head positioned adjacent to the holding stage for polishing the wafer by pressing a polishing tool against the wafer on the holding stage; a stage rotation mechanism for rotating the holding stage about its axis; a vibration sensor for detecting vibrations of the holding stage when the holding stage is rotating; and a vibration analysis unit for detecting abnormalities based on vibration signals indicating the vibrations output from the vibration sensor.

2. The polishing apparatus according to claim 1, wherein the polishing head is configured to polish the peripheral edge of the wafer by pressing a polishing tool against the peripheral edge of the wafer on the holding stage.

3. The polishing apparatus according to claim 1, wherein the vibration analysis unit is configured to generate an eccentricity alarm signal indicating that the wafer is eccentric with respect to the holding stage when the intensity of the vibration within a predetermined eccentricity monitoring frequency range exceeds an eccentricity threshold.

4. The polishing apparatus according to claim 1, wherein the vibration analysis unit is configured to generate a rotation alarm signal indicating a malfunction of the stage rotation mechanism when the intensity of the vibration within a predetermined rotation monitoring frequency range is lower than a rotation threshold.

5. The polishing apparatus according to claim 4, wherein the vibration analysis unit has a storage device that stores a plurality of rotation thresholds corresponding to different set rotation speeds of the holding stage, and the vibration analysis unit is configured to select the rotation threshold corresponding to the current set rotation speed of the holding stage from the plurality of rotation thresholds.

6. The polishing apparatus according to claim 1, wherein the vibration analysis unit is configured to determine the peak value of the vibration intensity during a predetermined polishing start period, and to generate a polishing head alarm signal indicating a malfunction of the polishing head when the peak value is smaller than the polishing start threshold.

7. The polishing apparatus according to claim 1, wherein the vibration analysis unit is configured to determine the peak value of the vibration intensity within a predetermined endpoint monitoring frequency range during a predetermined polishing final stage period, and to generate a polishing endpoint detection signal indicating the polishing endpoint of the wafer when the peak value is greater than the polishing endpoint threshold.

8. The polishing apparatus according to claim 1, wherein the vibration analysis unit is configured to determine the bottom value of the vibration intensity within a predetermined endpoint monitoring frequency range during a predetermined final polishing period, and generates a polishing endpoint detection signal indicating the polishing endpoint of the wafer when the bottom value is smaller than the polishing endpoint threshold.

9. The polishing apparatus according to claim 1, wherein the vibration sensor is attached to the polishing head.

10. The polishing apparatus according to claim 1, wherein the vibration sensor is attached to a tilt mechanism that tilts the polishing head relative to a holding stage.

11. The polishing apparatus according to claim 1, wherein the vibration sensor is attached to a bearing device that rotatably supports a stage shaft connected to the holding stage.

12. A polishing method comprising: rotating a holding stage that holds a wafer around its axis using a stage rotation mechanism; polishing the wafer by pressing a polishing tool against the wafer on the holding stage with a polishing head; detecting the vibration of the holding stage while the holding stage is rotating using a vibration sensor; and detecting an abnormality based on the vibration signal indicating the vibration output from the vibration sensor.

13. Polishing the wafer by pressing the polishing tool against the wafer on the holding stage with the polishing head means polishing the peripheral edge of the wafer by pressing the polishing tool against the peripheral edge of the wafer on the holding stage with the polishing head.

14. The polishing method according to claim 12, wherein detecting an anomaly based on the vibration signal includes generating an eccentricity alarm signal indicating that the wafer is eccentric with respect to the holding stage when the intensity of the vibration within a predetermined eccentricity monitoring frequency range exceeds an eccentricity threshold.

15. The polishing method according to claim 12, wherein detecting an anomaly based on the vibration signal includes generating a rotation alarm signal indicating a malfunction of the stage rotation mechanism when the intensity of the vibration within a predetermined rotation monitoring frequency range is lower than a rotation threshold.

16. The polishing method according to claim 15, wherein detecting an anomaly based on the vibration signal further comprises selecting the rotation threshold corresponding to the current set rotation speed of the holding stage from a plurality of rotation thresholds corresponding to different set rotation speeds of the holding stage.

17. The polishing method according to claim 12, wherein detecting an abnormality based on the vibration signal includes determining the peak value of the vibration intensity during a predetermined polishing start period, and generating a polishing head alarm signal indicating a malfunction of the polishing head when the peak value is smaller than a polishing start threshold.

18. The polishing method according to claim 12, further comprising determining the peak value of the vibration intensity within a predetermined endpoint monitoring frequency range during a predetermined final polishing period, and generating a polishing endpoint detection signal indicating the polishing endpoint of the wafer when the peak value is greater than a polishing endpoint threshold.

19. The polishing method according to claim 12, further comprising determining a bottom value of the vibration intensity within a predetermined endpoint monitoring frequency range during a predetermined final polishing period, and generating a polishing endpoint detection signal indicating the polishing endpoint of the wafer when the bottom value is smaller than a polishing endpoint threshold.

20. The polishing method according to claim 12, wherein the vibration sensor is attached to the polishing head.

21. The polishing method according to claim 12, wherein the vibration sensor is attached to a tilt mechanism that tilts the polishing head relative to a holding stage.

22. The polishing method according to claim 12, wherein the vibration sensor is attached to a bearing device that rotatably supports a stage shaft connected to the holding stage.

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