Polishing method and polishing apparatus

Abstract

This technology provides a way to stabilize the pressure control of the polishing head when the polishing rate changes significantly during the polishing of workpieces such as wafers. [Solution] The polishing method calculates multiple polishing rates for multiple regions on the surface of the workpiece W during polishing of the workpiece W, detects multiple change points in the multiple polishing rates, and before detecting the multiple change points in the multiple polishing rates, the polishing head 1 performs a polishing amount control operation in which it polishes multiple regions of the workpiece W by the same amount, and after detecting the multiple change points in the multiple polishing rates, the polishing head 1 performs a profile control operation in which it polishes multiple regions of the workpiece W so that the film thickness profile of the workpiece W reaches the target film thickness profile.

Description

Technical Field

[0001] The present invention relates to a technique for polishing workpieces such as wafers, circular substrates, and square substrates, and particularly to a technique for changing a polishing control operation based on the polishing rate of a workpiece.

Background Art

[0002] The manufacturing process of semiconductor devices includes various processes such as a process of polishing an insulating film such as SiO2 and a process of polishing a metal film such as copper and tungsten. Polishing of a wafer is performed using a polishing apparatus. The polishing apparatus generally includes a polishing table that supports a polishing pad, a polishing head that presses the wafer against the polishing pad, and a slurry supply nozzle that supplies slurry onto the polishing pad. While rotating the polishing table, slurry is supplied to the polishing pad on the polishing table, and the polishing head presses the wafer against the polishing pad. The wafer is brought into sliding contact with the polishing pad in the presence of the slurry. The surface of the wafer is flattened by a combination of the chemical action of the slurry and the mechanical action of the abrasive grains contained in the slurry and the polishing pad.

[0003] The polishing head has a plurality of pressure chambers corresponding to a plurality of regions of the wafer. During polishing of the wafer, these pressure chambers are filled with a compressed gas (for example, compressed air), and the internal pressure of the pressure chamber is applied to the wafer. During polishing of the wafer, the film thickness of the wafer is measured by a film thickness sensor, and the current film thickness profile of the wafer is obtained. The pressure in each pressure chamber of the polishing head is controlled so that this current film thickness profile reaches the target film thickness profile.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

[0005] When the film to be polished on a wafer is a metal film such as copper, the metal film may react with oxygen in the air before polishing, and a native oxide film may form on the metal film over time. This native oxide film coexists in equilibrium with the metal film and is highly stable both thermally and structurally.

[0006] When a metal film covered with a native oxide film is polished using the polishing apparatus described above, the native oxide film is more difficult to polish than the metal film. In other words, the polishing rate (also called the removal rate) of the native oxide film is usually lower than the polishing rate of the metal film. In such cases, the pressure in the pressure chamber of the polishing head is increased to raise the polishing rate of the native oxide film. After the native oxide film is removed, the metal film is polished, and the polishing rate changes significantly. As a result, the pressure in the pressure chamber drops sharply, causing pressure hunting (large fluctuations) and making the pressure control in the pressure chamber unstable. Similar problems can occur when the wafer surface is composed of a layered structure made of different materials.

[0007] Therefore, the present invention provides a technology that can stabilize the pressure control of the polishing head when the polishing rate changes significantly during the polishing of a workpiece such as a wafer. [Means for solving the problem]

[0008] In one embodiment, a polishing method is provided, in which the workpiece is polished by pressing the surface of the workpiece against a polishing pad with multiple pressure chambers of a polishing head while measuring the film thickness of the workpiece, multiple polishing rates for multiple regions within the surface of the workpiece are calculated during the polishing of the workpiece, multiple change points of the multiple polishing rates are detected, before the detection of the multiple change points of the multiple polishing rates, the polishing head performs a polishing amount control operation to polish the multiple regions of the workpiece by the same amount, and after the detection of the multiple change points of the multiple polishing rates, the polishing head performs a profile control operation to polish the multiple regions of the workpiece so that the film thickness profile of the workpiece reaches a target film thickness profile.

[0009] In one embodiment, the polishing amount control operation includes polishing the plurality of regions of the workpiece with the polishing head such that the surface shape of the workpiece shown in the initial film thickness profile at the start of polishing the workpiece is maintained. In one embodiment, the multiple change points of the multiple polishing rates are detected when at least one of a first detection condition and a second detection condition is met, the first detection condition being that each of the multiple polishing rates reaches a reference rate, and the second detection condition being that the polishing amount of each of the multiple regions of the workpiece reaches a reference polishing amount. In one embodiment, after all of the multiple change points of the multiple polishing rates corresponding to each of the multiple regions of the workpiece are detected, the polishing amount control operation is switched to the profile control operation. In one embodiment, the workpiece has a surface structure including a first film and a second film formed beneath the first film, and the plurality of change points are the points in time when the first film is removed. In one embodiment, the polishing rate of the first film is different from that of the second film.

[0010] In one embodiment, a polishing apparatus is provided comprising: a polishing table supporting a polishing pad; a polishing head having a plurality of pressure chambers for pressing the surface of a workpiece against the polishing pad; a film thickness sensor for measuring the film thickness of the workpiece; a pressure regulating device for adjusting the pressure in the plurality of pressure chambers; and a polishing control unit that controls the operation of the pressure regulating device to control the pressure of the polishing head, wherein the polishing control unit calculates a plurality of polishing rates for a plurality of regions on the surface of the workpiece, detects a plurality of change points in the plurality of polishing rates, and before detecting the plurality of change points in the plurality of polishing rates, commands the pressure regulating device to perform a polishing amount control operation to cause the polishing head to polish the plurality of regions of the workpiece by the same amount, and after detecting the plurality of change points in the plurality of polishing rates, commands the pressure regulating device to cause the polishing head to perform a profile control operation to polish the plurality of regions of the workpiece so that the film thickness profile of the workpiece reaches a target film thickness profile.

[0011] In one embodiment, the polishing control unit is configured to create an initial film thickness profile of the workpiece at the start of polishing from a plurality of measurement points of the initial film thickness of the workpiece, and during the polishing amount control operation, to give a command to the pressure regulating device to polish the plurality of regions of the workpiece with the polishing head so that the surface shape of the workpiece shown in the initial film thickness profile is maintained. In one embodiment, the polishing control unit is configured to detect the plurality of change points of the plurality of polishing rates when at least one of a first detection condition and a second detection condition is met, wherein the first detection condition is that each of the plurality of polishing rates reaches a reference rate, and the second detection condition is that the polishing amount of each of the plurality of regions of the workpiece reaches a reference polishing amount. In one embodiment, the polishing control unit is configured to switch the pressure control of the polishing head from the polishing amount control operation to the profile control operation after all of the multiple change points of the multiple polishing rates corresponding to each of the multiple regions of the workpiece have been detected. In one embodiment, the workpiece has a surface structure including a first film and a second film formed beneath the first film, and the plurality of change points are the points in time when the first film is removed. In one embodiment, the polishing rate of the first film is different from that of the second film. [Effects of the Invention]

[0012] Before a change in the polishing rate is detected, the profile control operation is not performed; instead, the polishing amount control operation is performed. This polishing amount control operation is a quantitative polishing operation that polishes multiple areas of the workpiece by the same amount. During the polishing amount control operation, the surface shape of the workpiece is maintained, so the pressure changes in the multiple pressure chambers of the polishing head are small. A change in the polishing rate means that the first film constituting the exposed surface of the workpiece has been removed, and a second film made of a different material from the first film has been exposed. Polishing of the second film is performed based on the profile control operation until the target film thickness of the workpiece is reached. Therefore, during the profile control operation, the same material of the second film is removed, so the polishing rate does not change significantly. As a result, the profile control operation, i.e., the pressure control of the polishing head, can be stabilized. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic diagram showing one embodiment of a polishing apparatus. [Figure 2] This is a cross-sectional view showing one embodiment of a polishing head. [Figure 3] This is a cross-sectional view showing an example of the surface structure of a workpiece before polishing. [Figure 4] This is a flowchart showing one embodiment of a method for polishing a workpiece. [Figure 5]A graph showing the change in the film thickness profile of a workpiece polished by a polishing method executed according to the embodiment shown in FIG. 4. [Figure 6] A graph showing the change in the polishing rate corresponding to the embodiment of FIG. 5. [Figure 7] A graph showing the change in the film thickness profile of a workpiece polished by a polishing method that only executes the profile control operation. [Figure 8] A graph showing the change in the polishing rate corresponding to the comparative example of FIG. 7. [Figure 9] A flowchart showing an embodiment of detecting a plurality of change points of a plurality of polishing rates.

Best Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an embodiment of a polishing apparatus. As shown in FIG. 1, the polishing apparatus includes a polishing table 3 that supports a polishing pad 2, a polishing head 1 that presses a workpiece W against the polishing pad 2, a table motor 6 that rotates the polishing table 3, a polishing liquid supply nozzle 5 for supplying a polishing liquid such as slurry onto the polishing pad 2, and a polishing control unit 9 for controlling the operation of the polishing apparatus. The upper surface of the polishing pad 2 constitutes a polishing surface 2a for polishing the workpiece W.

[0015] The polishing head 1 is connected to the head shaft 10, which is connected to the polishing head rotating device 15. The polishing head rotating device 15 is configured to rotate the polishing head 1 together with the head shaft 10 in the direction indicated by the arrow. The configuration of the polishing head rotating device 15 is not particularly limited, but in one example, the polishing head rotating device 15 includes an electric motor, a belt, a pulley, etc. The polishing table 3 is connected to the table motor 6, which is configured to rotate the polishing table 3 and the polishing pad 2 in the direction indicated by the arrow. The polishing head 1, the polishing head rotating device 15, and the table motor 6 are connected to the polishing control unit 9, and the operation of the polishing head 1, the polishing head rotating device 15, and the table motor 6 is controlled by the polishing control unit 9.

[0016] The workpiece W is polished as follows: The table motor 6 and the polishing head rotating device 15 rotate the polishing table 3 and the polishing head 1 in the direction indicated by the arrows in Figure 1, while polishing fluid is supplied from the polishing fluid supply nozzle 5 to the polishing surface 2a of the polishing pad 2 on the polishing table 3. As the workpiece W is rotated by the polishing head 1, the workpiece W is pressed against the polishing surface 2a of the polishing pad 2 by the polishing head 1 while polishing fluid is present on the polishing pad 2. The surface of the workpiece W is polished by the chemical action of the polishing fluid and the mechanical action of the abrasive grains contained in the polishing fluid and / or the polishing pad 2.

[0017] The polishing control unit 9 comprises a storage device 9a in which a program is stored, and an arithmetic unit 9b that performs calculations according to the instructions contained in the program. The polishing control unit 9 is composed of at least one computer. The storage device 9a comprises a main memory such as random access memory (RAM) and an auxiliary storage device such as a hard disk drive (HDD) or solid-state drive (SSD). Examples of arithmetic units 9b include a CPU (central processing unit) and a GPU (graphics processing unit). However, the specific configuration of the polishing control unit 9 is not limited to these examples.

[0018] The polishing apparatus further includes a film thickness sensor 21 for measuring the film thickness of a workpiece W on a polishing pad 2. The film thickness sensor 21 is fixed to the polishing table 3 and rotates with the polishing table 3. The position of the film thickness sensor 21 is such that it crosses the surface of the workpiece W on the polishing pad 2 each time the polishing table 3 and polishing pad 2 complete one rotation. The film thickness sensor 21 is configured to measure the film thickness at multiple measurement points on the surface of the workpiece W each time it crosses the surface of the workpiece W. Specific examples of the film thickness sensor 21 include optical film thickness sensors and eddy current film thickness sensors, but the type of film thickness sensor 21 is not particularly limited as long as it can measure the film thickness of the workpiece W. The film thickness sensor 21 is electrically connected to the polishing control unit 9, and the measured film thickness is transmitted from the film thickness sensor 21 to the polishing control unit 9. The measured film thickness may be a numerical value that directly indicates the film thickness, or it may be an index or physical quantity that indirectly indicates the film thickness.

[0019] Figure 2 is a cross-sectional view showing one embodiment of the polishing head 1. The polishing head 1 comprises a carrier 31 fixed to the end of the head shaft 10, an elastic membrane 34 attached to the lower part of the carrier 31, and a retainer ring 32 positioned below the carrier 31. The retainer ring 32 is positioned around the elastic membrane 34.

[0020] The elastic membrane 34 comprises a contact portion 35 having a contact surface 35a that can contact the upper surface of the workpiece W, and inner wall portions 36a, 36b, 36c and an outer wall portion 36d connected to the contact portion 35. The contact portion 35 has substantially the same size and shape as the upper surface of the workpiece W. The inner wall portions 36a, 36b, 36c and the outer wall portion 36d are endless walls arranged concentrically. The outer wall portion 36d is located outside the inner wall portions 36a, 36b, 36c and is arranged to surround the inner wall portions 36a, 36b, 36c.

[0021] Multiple (four in this embodiment) pressure chambers C1, C2, C3, and C4 are provided between the elastic membrane 34 and the carrier 31. The pressure chambers C1, C2, C3, and C4 are formed by the contact portion 35, inner wall portions 36a, 36b, and 36c, and outer wall portion 36d of the elastic membrane 34. In this embodiment, the elastic membrane 34 forms four pressure chambers C1 to C4, but in one embodiment, the elastic membrane 34 may form three pressure chambers, or it may form five or more pressure chambers.

[0022] An annular membrane (rolling diaphragm) 37 is positioned between the carrier 31 and the retainer ring 32, and a pressure chamber C5 is formed inside this membrane 37. Gas transfer lines F1, F2, F3, F4, and F5 are connected to the pressure chambers C1, C2, C3, C4, and C5, respectively. The gas transfer lines F1, F2, F3, F4, and F5 extend via a rotary joint 40 attached to the head shaft 10.

[0023] Gas transfer lines F1, F2, F3, F4, and F5 are connected to a compressed gas supply source (not shown) which serves as a utility supply source in the factory where the polishing equipment is installed. Compressed gas, such as compressed air, is supplied to pressure chambers C1, C2, C3, C4, and C5, respectively, through gas transfer lines F1, F2, F3, F4, and F5.

[0024] Pressure regulators Ra1, Ra2, Ra3, Ra4, and Ra5, which are pressure regulating devices, are installed on the gas transfer lines F1, F2, F3, F4, and F5, respectively. Compressed gas from the compressed gas supply source is supplied independently to the pressure chambers C1 to C5 through the pressure regulators Ra1 to Ra5 ​​and the gas transfer lines F1 to F5. The pressure regulators Ra1 to Ra5 ​​are configured to regulate the pressure of the compressed gas in the pressure chambers C1 to C5.

[0025] The pressure regulators Ra1 to Ra5, which are pressure regulating devices, are connected to the polishing control unit 9. The operation of the pressure regulators Ra1 to Ra5 ​​is controlled by the polishing control unit 9. The polishing control unit 9 sends pressure command values ​​for pressure chambers C1 to C5 to the pressure regulators Ra1 to Ra5, and the pressure regulators Ra1 to Ra5 ​​operate so that the pressure in pressure chambers C1 to C5 is maintained at the corresponding pressure command value.

[0026] The pressure regulators Ra1 to Ra5 ​​can independently change the pressure within the pressure chambers C1 to C5. Therefore, the polishing head 1 can independently adjust the polishing pressure on four corresponding areas of the workpiece W, namely the central part, the inner middle part, the outer middle part, and the edge part, and the pressing force of the polishing pad 2 of the retainer ring 32 against the polishing surface 2a. For example, the polishing head 1 can press different areas of the workpiece W surface against the polishing surface 2a of the polishing pad 2 with different polishing pressures. Therefore, the polishing head 1 can control the film thickness profile of the workpiece W to achieve a target film thickness profile.

[0027] Figure 3 is a cross-sectional view showing an example of the surface structure of a workpiece W before polishing. As shown in Figure 3, the workpiece W before polishing has a surface structure including a first film 101 and a second film 102 formed beneath the first film 101. Examples of workpiece W include wafers, substrates, wiring boards, and square substrates used in the manufacture of semiconductor devices. In this embodiment, the second film 102 is a metal film, and the first film 101 is a native oxide film covering the second film 102. The native oxide film is formed by the reaction of a metal film (e.g., a copper film) with oxygen in the air. The first film 101 has a uniform thickness across the entire surface of the workpiece W.

[0028] However, the second film 102 is not limited to a metal film. In other examples, the second film 102 may be an insulating film. In particular, when the first film 101 is a low-dielectric constant film (low-k film), the polishing rate of the first film 101 may be lower than that of the insulating film (e.g., SiO2) of the second film 102. In another example, the first film 101 is a metal film made of a first metal, and the second film 102 is a metal film made of a second metal different from the first metal. In other examples, the polishing rate of the first film 101 may be higher than that of the second film 102. In all of the examples described above, the polishing rate (also called the removal rate) of the first film 101 is different from the polishing rate of the second film 102. Here, the polishing rate is the film thickness reduced by polishing per unit time.

[0029] The film thickness sensor 21 shown in Figure 1 measures the film thickness at multiple measurement points on the surface of the workpiece W during polishing and sends the multiple measured film thickness values ​​to the polishing control unit 9. The polishing control unit 9 is configured to create a current film thickness profile of the workpiece W from the multiple measured film thickness values. The film thickness profile is the distribution of film thickness in the radial direction of the workpiece W.

[0030] Next, an embodiment of a method for polishing a workpiece W using the polishing apparatus described above will be explained. Figure 4 is a flowchart showing an embodiment of the method for polishing a workpiece W. In step 101, polishing of the workpiece W is started by pressing the surface of the workpiece W against the polishing pad 2 using the multiple pressure chambers C1, C2, C3, and C4 of the polishing head 1. During polishing of the workpiece W, the film thickness of the workpiece W is measured by the film thickness sensor 21, and the measured value of the film thickness of the workpiece W is sent to the polishing control unit 9.

[0031] In step 102, the polishing control unit 9 creates an initial film thickness profile of the workpiece W when polishing of the workpiece W begins. More specifically, the polishing control unit 9 creates an initial film thickness profile of the workpiece W from multiple measurement points of the initial film thickness at the start of polishing of the workpiece W. The initial film thickness of the workpiece W is the film thickness at the start of polishing of the workpiece W. Therefore, the initial film thickness profile is the film thickness profile of the workpiece W at the start of polishing. After polishing of the workpiece W begins, the polishing control unit 9 similarly periodically creates a film thickness profile from multiple measurement points of the film thickness of the workpiece W.

[0032] In step 103, the polishing head 1 performs a polishing amount control operation. This polishing amount control operation is a quantitative polishing operation that polishes multiple areas of the workpiece W by the same amount. That is, the polishing control unit 9 gives a command to the pressure regulators Ra1 to Ra4 (see Figure 2), which are pressure regulating devices, to cause the polishing head 1 to polish multiple areas of the workpiece W by the same amount. The multiple areas of the workpiece W correspond to the multiple pressure chambers C1, C2, C3, C4 (see Figure 2) of the polishing head 1. In other words, the polishing head 1 applies the pressure from the multiple pressure chambers C1, C2, C3, C4 to multiple areas of the workpiece W and polishes the surface of the workpiece W.

[0033] The polishing amount control operation includes polishing multiple areas of the workpiece W with the polishing head 1 so as to maintain the surface shape of the workpiece W shown in the initial film thickness profile. That is, in the polishing amount control operation, the polishing control unit 9 commands the pressure regulators Ra1 to Ra4 (see Figure 2), which are pressure regulating devices, to polish multiple areas of the workpiece W with the polishing head 1 so as to maintain the surface shape of the workpiece W shown in the initial film thickness profile. Specifically, the pressure regulators Ra1 to Ra4 adjust the pressure in the multiple pressure chambers C1, C2, C3, C4 of the polishing head 1 so as to maintain the surface shape of the workpiece W shown in the initial film thickness profile. Therefore, during the polishing amount control operation, the overall film thickness of the workpiece W decreases, while the surface shape of the workpiece W is maintained at a constant level. Since the surface shape of the workpiece W is maintained during the polishing amount control operation, the pressure changes in the multiple pressure chambers C1, C2, C3, C4 of the polishing head 1 are small.

[0034] As soon as the polishing amount control operation starts, the polishing control unit 9 calculates the polishing rates for the multiple regions on the surface of the workpiece W. During the polishing amount control operation, the multiple regions of the workpiece W are polished by the same amount, so the multiple polishing rates for the multiple regions of the workpiece W remain constant.

[0035] In step 104, the polishing control unit 9 detects multiple change points in multiple polishing rates. The method for detecting each change point in polishing rate will be described later, but in one embodiment, the point at which the polishing rate of each region of the workpiece W reaches a reference rate is the change point in the polishing rate. The polishing rate changes significantly when the surface structure of the workpiece W changes. In the example shown in Figure 3, the change point in the polishing rate is the point at which the first film 101 constituting the exposed surface of the workpiece W is removed and the second film 102, made of a different material from the first film 101, is exposed.

[0036] In step 105, after detecting multiple change points of multiple polishing rates, a profile control operation is performed. The profile control operation is a feedback polishing operation in which multiple areas of the workpiece W are polished by the polishing head 1 so that the film thickness profile of the workpiece W reaches the target film thickness profile. During the profile control operation, the polishing control unit 9 creates a film thickness profile (i.e., the current film thickness profile) from multiple film thickness measurements sent from the film thickness sensor 21.

[0037] The polishing control unit 9 determines the pressures in multiple pressure chambers C1, C2, C3, and C4 to minimize the difference between the current film thickness profile and the target film thickness profile, and transmits the determined pressure command value to pressure regulators Ra1 to Ra4. The pressure regulators Ra1 to Ra4 then adjust the pressures in the multiple pressure chambers C1, C2, C3, and C4 of the polishing head 1 according to the pressure command value. Through this pressure control of the polishing head 1, the film thickness profile of the workpiece W approaches the target film thickness profile. The target film thickness profile is pre-stored in the storage device 9a of the polishing control unit 9. One embodiment of the profile control operation can be applied to known technology, for example, the technology disclosed in Japanese Patent Application Publication No. 2015-168015.

[0038] In step 106, the profile control operation is terminated when the target film thickness of the workpiece W is reached. Polishing of the workpiece W is terminated when the target film thickness is reached or when the second film 102 is completely removed.

[0039] Detecting a change in the polishing rate indicates that the first film 101, which constitutes the exposed surface of the workpiece W, has been removed, and polishing of the second film 102, which is made of a different material from the first film 101, has begun. Polishing of the second film 102 is performed based on the profile control operation until the target film thickness of the workpiece W is reached. During the profile control operation, the same material of the second film 102 is removed, so the polishing rate does not change significantly. As a result, the profile control operation, i.e., the pressure control of the polishing head 1, can be stabilized.

[0040] If the pressure control of the polishing head 1 switches from polishing amount control operation to profile control operation while a portion of the first film 101 remains on the workpiece W, the profile control operation tends to become unstable when the remaining portion of the first film 101 is removed and the second film 102 is exposed. Therefore, in one embodiment, the polishing control unit 9 is configured to switch the pressure control of the polishing head 1 from polishing amount control operation to profile control operation after all of the multiple change points of multiple polishing rates corresponding to multiple regions of the workpiece W have been detected. With this operation, the profile control operation is started after the entire first film 101 has been removed from the workpiece W, thus ensuring the stability of the profile control operation.

[0041] Figure 5 is a graph showing the change in the film thickness profile of a workpiece W polished by a polishing method performed according to the embodiment shown in Figure 4. In Figure 5, the vertical axis represents the film thickness of the workpiece W, and the horizontal axis represents the radial position of the workpiece W. The multiple curves shown in Figure 5 represent the film thickness profile that changes with polishing time. As shown in Figure 5, as the workpiece W is polished, the film thickness profile changes from the initial film thickness profile to the target film thickness profile.

[0042] The polishing amount control operation is performed from the start of polishing of the workpiece W until a point of change in the polishing rate is detected. As can be seen from Figure 5, during the polishing amount control operation, the film thickness of the workpiece W decreases, but the shape of the film thickness profile, i.e., the surface shape of the workpiece W, remains unchanged.

[0043] When multiple polishing rates in multiple regions of the workpiece W reach their respective change points, the pressure control of the polishing head 1 switches from polishing volume control operation to profile control operation. The profile control operation continues until the target film thickness is reached.

[0044] Figure 6 is a graph showing the change in polishing rate corresponding to the embodiment in Figure 5. In Figure 6, the vertical axis represents the film thickness of the workpiece W, and the horizontal axis represents the polishing time of the workpiece W. The symbol RL shown in Figure 6 represents the range in which the points of change in the polishing rate of multiple regions of the workpiece W corresponding to pressure chambers C1 to C4 are detected. That is, the multiple points of change in the polishing rate are contained within the range RL. In this embodiment, after all of the multiple points of change in the multiple polishing rates of multiple regions of the workpiece W have been detected, the pressure control of the polishing head 1 is switched from polishing amount control operation to profile control operation. As shown in Figure 6, the multiple polishing rates during profile control operation are maintained almost constant without hunting.

[0045] The polishing rate before multiple change points of multiple polishing rates are detected is the polishing rate of the first film 101 shown in Figure 3, and the polishing rate after multiple change points of multiple polishing rates are detected is the polishing rate of the second film 102 shown in Figure 3. In the embodiment shown in Figure 6, the polishing rate of the first film 101 is lower than the polishing rate of the second film 102 (i.e., the slope angle of the polishing rate of the first film 101 is smaller than the slope angle of the polishing rate of the second film 102).

[0046] Figure 7 is a graph illustrating a comparative example, more specifically, a graph showing the change in the film thickness profile of a workpiece W polished by a polishing method that performs only profile control operations. In this comparative example, profile control operations are performed from the start to the end of polishing of the workpiece W, and polishing amount control operations are not performed. As shown in Figure 7, multiple regions of the workpiece W are polished unevenly from the start of polishing until a point of change in the polishing rate is detected. This is because the pressure in a certain pressure chamber changes significantly in order to bring the initial film thickness profile closer to the target film thickness profile.

[0047] Figure 8 is a graph showing the change in polishing rate corresponding to the comparative example in Figure 7. As shown in Figure 8, the points at which the polishing rate change points were detected for multiple regions of the workpiece W corresponding to pressure chambers C1 to C4 fall within the range RL, but the range RL shown in Figure 8 is larger than the range RL shown in Figure 6. This indicates that it takes longer for the multiple polishing rates to converge. Furthermore, the polishing rate in a certain region hunts (fluctuations) after its change point. As a result, the pressure control of the polishing head 1 is unstable until the target film thickness is reached.

[0048] As can be seen from the comparison between Figure 6 and Figure 8, this embodiment, which performs the polishing amount control operation before the point of change in the polishing rate, can stabilize the profile control operation after the point of change in the polishing rate.

[0049] Figure 9 is a flowchart showing one embodiment of step 104 in Figure 4, which detects multiple change points of multiple polishing rates. In step 201, the polishing control unit 9 calculates the initial polishing rate of the workpiece W immediately after the polishing of the workpiece W begins. Since the polishing rate is the amount of reduction in the film thickness of the workpiece W per unit time, the polishing control unit 9 can calculate the initial polishing rate from the film thickness of the workpiece W measured by the film thickness sensor 21.

[0050] In step 202, the polishing control unit 9 calculates the current polishing rate and current polishing amount for each of the multiple regions of the workpiece W, thereby obtaining multiple current polishing rates and multiple current polishing amounts corresponding to the multiple regions. The polishing amount for each region of the workpiece W is the difference between the film thickness at the start of polishing the workpiece W and the current film thickness. In step 203, the polishing control unit 9 determines whether the current polishing rate of each of the multiple regions has reached the reference rate.

[0051] In one embodiment, the reference rate is a polishing rate determined based on the initial polishing rate calculated in step 201. For example, the reference rate is obtained by multiplying the initial polishing rate by a reference ratio. The reference ratio is a reference value for the ratio of the polishing rate after the change point to the polishing rate before the change point.

[0052] In other embodiments, the reference rate may be a polishing rate obtained from the polishing results of a reference workpiece having the same surface structure. More specifically, the reference rate is the polishing rate of the reference workpiece after a point of change in the polishing rate of the reference workpiece has been detected.

[0053] If the current polishing rate has not reached the baseline rate (NO in step 203), the process flow returns to step 202. When the current polishing rate reaches the reference rate (YES in step 203), the polishing control unit 9 determines in step 204 whether the current polishing amount of each of the multiple regions of the workpiece W has reached the reference polishing amount. In one embodiment, the reference polishing amount is the amount of reduction in film thickness (i.e., polishing amount) from the start of polishing of the reference workpiece to the point of change in the polishing rate.

[0054] If the current polishing amount has not reached the standard polishing amount (NO in step 204), the process flow returns to step 202. When the current polishing amount reaches the standard polishing amount (YES in step 204), the polishing control unit 9 determines in step 205 that multiple polishing rates in multiple regions of the workpiece W have reached their respective change points. In this way, the polishing control unit 9 can detect multiple change points in polishing rates.

[0055] Step 203 described above is a first detection condition for detecting multiple change points of multiple polishing rates, and Step 204 described above is a second detection condition for detecting multiple change points of multiple polishing rates. In the embodiment shown in Figure 9, multiple change points of multiple polishing rates are detected when both the first and second detection conditions are met.

[0056] In other embodiments, either step 203 or step 204 described above may be omitted. In yet another embodiment, step 203 described above may be performed after step 204. In other words, multiple points of change in multiple polishing rates are detected when at least one of the first detection condition and the second detection condition is met. The first detection condition is that each of the multiple polishing rates reaches a baseline rate, and the second detection condition is that the polishing amount of each of the multiple regions of the workpiece W reaches a baseline polishing amount.

[0057] 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. [Explanation of symbols]

[0058] 1 Polishing head 2 polishing pads 2a Polished surface 3 Polishing Table 5. Polishing fluid supply nozzle 6 Table motors 9 Polishing Control Unit 10 Head Shaft 15. Polishing head rotation device 21 Film Thickness Sensor 31 Careers 32 Retainer Rings 34 Elastic membrane 35 Contact area 35a Contact surface 36a,36b,36c Inner wall 36d Exterior wall 37 Membrane (Rolling Diaphragm) 40 Rotary Joint C1,C2,C3,C4,C5 Pressure chamber F1, F2, F3, F4, F5 Gas Transfer Line Ra1, Ra2, Ra3, Ra4, Ra5 Pressure Regulator (Pressure Regulating Device) W Workpiece

Claims

1. While measuring the film thickness of the workpiece, the workpiece surface is pressed against the polishing pad by multiple pressure chambers of the polishing head, thereby polishing the workpiece. During the polishing of the workpiece, multiple polishing rates for multiple regions within the surface of the workpiece are calculated. Multiple change points of the aforementioned multiple polishing rates are detected, Before detecting the multiple change points of the multiple polishing rates, the polishing head performs a polishing amount control operation to polish the multiple regions of the workpiece by the same amount. A polishing method comprising: detecting the plurality of change points of the plurality of polishing rates, the polishing head performs a profile control operation to polish the plurality of regions of the workpiece so that the film thickness profile of the workpiece reaches a target film thickness profile.

2. The polishing method according to claim 1, wherein the polishing amount control operation includes polishing the plurality of regions of the workpiece with the polishing head such that the surface shape of the workpiece shown in the initial film thickness profile at the start of polishing of the workpiece is maintained.

3. The multiple change points of the multiple polishing rates are detected when at least one of the first detection condition and the second detection condition is met. The first detection condition is that each of the multiple polishing rates reaches a reference rate. The polishing method according to claim 1, wherein the second detection condition is that the polishing amount of each of the plurality of regions of the workpiece reaches a reference polishing amount.

4. The polishing method according to claim 1, wherein after all of the multiple change points of the multiple polishing rates corresponding to each of the multiple regions of the workpiece have been detected, the polishing amount control operation is switched to the profile control operation.

5. The workpiece has a surface structure including a first film and a second film formed beneath the first film. The polishing method according to claim 1, wherein the plurality of change points are the points at which the first film is removed.

6. The polishing method according to claim 5, wherein the polishing rate of the first film is different from the polishing rate of the second film.

7. A polishing table that supports the polishing pad, A polishing head having multiple pressure chambers that press the surface of the workpiece against the polishing pad, A film thickness sensor for measuring the film thickness of the workpiece, A pressure regulating device that adjusts the pressure in the plurality of pressure chambers, The polishing control unit controls the pressure of the polishing head by controlling the operation of the pressure adjustment device, The polishing control unit, The polishing rates of multiple regions within the surface of the workpiece are calculated, Multiple change points of the aforementioned multiple polishing rates are detected, Before detecting the multiple change points of the multiple polishing rates, a command is given to the pressure regulating device to perform a polishing amount control operation that causes the polishing head to polish the multiple areas of the workpiece by the same amount. A polishing apparatus configured to detect the plurality of change points of the plurality of polishing rates, and then to issue a command to the pressure regulator to cause the polishing head to perform a profile control operation to polish the plurality of regions of the workpiece so that the film thickness profile of the workpiece reaches a target film thickness profile.

8. The polishing control unit, An initial film thickness profile of the workpiece at the start of polishing is created from multiple measurement points of the initial film thickness of the workpiece. The polishing apparatus according to claim 7, wherein during the polishing amount control operation, a command is given to the pressure regulating device to cause the polishing head to polish the plurality of regions of the workpiece so as to maintain the surface shape of the workpiece shown in the initial film thickness profile.

9. The polishing control unit is configured to detect the plurality of change points of the plurality of polishing rates when at least one of the first detection condition and the second detection condition is met. The first detection condition is that each of the multiple polishing rates reaches a reference rate. The polishing apparatus according to claim 7, wherein the second detection condition is that the polishing amount of each of the plurality of regions of the workpiece reaches a reference polishing amount.

10. The polishing apparatus according to claim 7, wherein the polishing control unit is configured to switch the pressure control of the polishing head from the polishing amount control operation to the profile control operation after all of the multiple change points of the multiple polishing rates corresponding to each of the multiple regions of the workpiece have been detected.

11. The workpiece has a surface structure including a first film and a second film formed beneath the first film. The polishing apparatus according to claim 7, wherein the plurality of change points are the points at which the first film is removed.

12. The polishing apparatus according to claim 11, wherein the polishing rate of the first film is different from the polishing rate of the second film.

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