Polishing apparatus and polishing method

Abstract

The objective of the present invention is to provide a polishing device capable of polishing a workpiece, such as a wafer, under appropriate polishing conditions by monitoring the distribution of liquid amounts, such as polishing liquid or chemical liquid, on the polishing surface of a polishing pad. The polishing device comprises a polishing table (5) that supports a polishing pad (2), a polishing head (7) that presses a workpiece (W) against a polishing surface (2a) of the polishing pad (2), a liquid supply device (8) that supplies liquid onto the polishing surface (2a), a liquid monitoring device (12) that acquires optical information included in light from multiple points on the polishing surface (2a), an optical information analysis unit (13) that determines the distribution of liquid amount on the polishing surface (2a) from the optical information, and an operation control unit (47) that controls the operation of the polishing device.

Description

Technology Field

[0001] The present invention relates to a polishing apparatus and a polishing method for polishing a workpiece, such as a wafer, substrate, or panel, by pressing it against the polishing surface of a polishing pad. In particular, the invention relates to a polishing apparatus and a polishing method for sliding contact of a workpiece with a polishing pad while a polishing liquid, such as a slurry, is present on the polishing surface of a polishing pad. Background Technology

[0002] In the manufacturing of semiconductor devices, various types of films are formed on wafers. In the wiring and contact formation process, the wafer is polished after the film deposition process to remove unnecessary parts of the film or surface irregularities. Chemical Mechanical Polishing (CMP) is a representative technology for wafer polishing. This CMP is performed by supplying a polishing liquid onto the polishing surface of a polishing pad while pressing the wafer against the polishing surface and making sliding contact. The film formed on the wafer is polished by a combination of chemical action caused by the chemical components of the polishing liquid supplied onto the polishing surface and mechanical action caused by abrasive particles contained in the polishing liquid and / or the polishing pad.

[0003] A polishing device for performing a CMP process is equipped with a polishing table that supports a polishing pad and a polishing head for pressing a wafer, which is the workpiece to be polished, against the polishing pad. This polishing device presses the wafer against the polishing surface of the polishing pad while supplying a polishing liquid from a liquid supply device onto the polishing surface of the polishing pad. At this time, by rotating the polishing table and the polishing head, the wafer makes sliding contact with the polishing surface, and the surface of the wafer is polished to be flat and mirror-like.

[0004] The precision required for each process in the manufacturing of modern semiconductor devices has already reached the order of several nanometers, and CMP is no exception. Furthermore, along with the high integration of semiconductor integrated circuits, miniaturization and multilayering are accelerating. Therefore, to realize this miniaturization and multilayering, it is required that the variation in residual film thickness after CMP be kept within the order of several nanometers across the entire wafer surface, even in CMP.

[0005] To reduce variations in residual film thickness, it is necessary to control various factors affecting the polishing rate, such as the surface temperature of the polishing pad during polishing, the amount of polishing liquid supplied, and the distribution of polishing liquid on the polishing pad. Additionally, in the CMP process, cleaning liquids such as chemicals or deionized water (DIW) are sometimes supplied onto the polishing pad via a liquid supply device instead of polishing liquid for the purpose of cleaning the wafer surface after polishing. The distribution of the cleaning liquid supply amount also affects the uniformity of the cleaning performance of the wafer surface.

[0006] Furthermore, cost reduction is required for each process in the manufacturing of semiconductor devices. In the CMP process, the polishing fluid is a particular target for cost reduction. The polishing fluid used in CMP is expensive, and the disposal of used fluid also incurs costs. Therefore, to reduce the operating costs of CMP equipment and the manufacturing costs of semiconductor devices, a reduction in the amount of polishing fluid used is required.

[0007] A liquid supply device typically supplies polishing liquid from a nozzle having a single supply port, and depending on the polishing process, performs operations such as oscillating the nozzle parallel to the polishing pad. Additionally, Patent Document 1 describes a device for efficiently supplying polishing liquid to the polishing surface of a polishing pad. Patent Document 1 discloses a nozzle having multiple polishing liquid supply ports and a nozzle having a slit-shaped supply port, and states that efficient polishing can be achieved by spreading the polishing liquid onto the polishing pad. Prior art literature

[0008] Japanese Patent Publication No. 2006-147773 The problem to be solved

[0009] As such, the amount of polishing liquid supplied during polishing and the distribution of the amount of polishing liquid on the polishing pad significantly affect polishing performance (variation in polishing rate) and polishing efficiency. Therefore, monitoring the distribution of the amount of polishing liquid on the polishing pad is necessary to maintain polishing performance and polishing efficiency.

[0010] Factors that cause changes in the distribution of polishing fluid on the polishing pad include equipment failure, changes in the physical properties (such as viscosity) of the polishing fluid caused by a rise in the polishing pad's temperature, and changes in the surface condition of the polishing pad. In cases where equipment failure is the cause, most are detected as abnormalities in the polishing fluid flow rate by flow sensors. For example, if the liquid supply device is a nozzle with a single supply port, a flow sensor is provided at each nozzle. Furthermore, if the liquid supply device is a nozzle with multiple supply ports, a flow sensor is provided in the main flow path communicating with the nozzle.

[0011] However, in the liquid supply device having the aforementioned multiple supply ports, if a blockage occurs in any of the multiple supply ports, the change in flow rate is distributed among the number of supply ports, resulting in a small change in the flow rate of the supply channel. Consequently, there are cases where an abnormality in the flow rate is not determined, and consequently, the blockage of the supply port may not be detected. To address this, one approach is to place multiple flow sensors at each of the multiple supply ports; however, since the number of flow sensors must be increased in proportion to the increase in supply ports, this inevitably entails an increase in sensor installation space and sensor costs.

[0012] In addition, the polishing pad undergoes wear due to polishing, and the distribution of the polishing liquid on the polishing pad surface changes due to variations in the amount of wear within the polishing pad surface. For example, if the dimensions (especially the depth of the groove) of the groove formed within the polishing pad surface decrease due to wear, even if the supply flow rate of the polishing liquid is normal, the distribution of the polishing liquid on the polishing pad surface changes, leading to changes or variations in the polishing rate distribution. Furthermore, these problems are the same even when the liquid supplied to the polishing surface is a chemical solution or pure water.

[0013] Therefore, the present invention provides a polishing apparatus and a polishing method capable of monitoring the distribution of liquid amounts, such as polishing liquid or chemical liquid, on the polishing surface of a polishing pad, and polishing a workpiece, such as a wafer, under appropriate polishing conditions based on the distribution of liquid amounts obtained from the monitoring. means of solving the problem

[0014] In one embodiment, a polishing device for polishing a workpiece is provided, comprising: a polishing table that supports a polishing pad; a polishing head that presses the workpiece against the polishing surface of the polishing pad; a liquid supply device that supplies liquid onto the polishing surface; a polishing table rotation device that rotates the polishing table; a polishing head rotation device that rotates the polishing head; a liquid monitoring device that acquires optical information included in light from a plurality of points on the polishing surface; an optical information analysis unit that determines the distribution of the amount of liquid on the polishing surface from the optical information; and an operation control unit that controls the operation of the polishing device.

[0015] In one embodiment, the operation control unit is configured to issue a command to the liquid monitoring device before supplying the liquid to acquire first optical information of a plurality of points on the polishing surface, and also to issue a command to the liquid monitoring device at the time of supplying the liquid to acquire second optical information of a plurality of points on the polishing surface, and the optical information analysis unit is configured to determine a first distribution from the first optical information, determine a second distribution from the second optical information, and determine the distribution of the liquid amount by subtracting the first distribution from the second distribution.

[0016] In one embodiment, the operation control unit is configured to issue a command to the liquid monitoring device to acquire optical information of multiple points on the polishing surface at multiple points in time during the polishing of the workpiece, and the optical information analysis unit is configured to acquire a temporal trend of the distribution of the liquid amount on the polishing surface from the optical information of multiple points on the polishing surface acquired at the multiple points in time.

[0017] In one embodiment, the operation control unit is configured to issue a command to the liquid monitoring device to acquire the optical information during an interval time before or after polishing the workpiece.

[0018] In one embodiment, the operation control unit is configured to issue a command to the liquid monitoring device to acquire initial optical information from multiple points on the polishing surface of the polishing pad in a non-polishing state and current optical information from multiple points on the polishing surface of the polishing pad in use for polishing, the optical information analysis unit determines an initial distribution of the liquid amount from the initial optical information and determines a current distribution of the liquid amount on the polishing surface from the current optical information, and the operation control unit is configured to calculate the difference between the initial distribution and the current distribution.

[0019] In one embodiment, the operation control unit is configured to issue a command to the liquid supply device so that, while the liquid monitoring device is acquiring the optical information, the liquid of a different type from the polishing liquid used for polishing the workpiece is supplied onto the polishing surface of the polishing pad.

[0020] In one embodiment, the polishing device further comprises a light source that irradiates the polishing surface with light having one or more wavelengths within the range of 200 nm to 1100 nm.

[0021] In one embodiment, the liquid monitoring device has a light detection sensor that measures the amount of light having one or more wavelengths within the range of 200 nm to 1100 nm.

[0022] In one embodiment, the optical information analysis unit is configured to determine the distribution of the liquid amount on the polished surface based on the measurement data of the light amount.

[0023] In one embodiment, the liquid monitoring device has an image sensor that generates a color image.

[0024] In one embodiment, the optical information analysis unit is configured to determine the distribution of the liquid amount on the polishing surface by analyzing the color distribution as the optical information appearing on the color image.

[0025] In one embodiment, the liquid monitoring device is arranged to acquire optical information of the plurality of points within a monitoring area located upstream of the polishing head in the rotational direction of the polishing table.

[0026] In one embodiment, the operation control unit is configured to calculate the difference between a plurality of distributions of the liquid amount on the polishing surface determined at a plurality of points in time during the polishing of the workpiece, and if the difference in distribution is greater than an allowable value, to change the polishing conditions for the workpiece in a direction that reduces the difference in distribution.

[0027] In one embodiment, the operation control unit is configured to recalculate the difference between a plurality of distributions of the liquid amount determined during the polishing of the workpiece after changing the polishing conditions, and if the difference in distribution is greater than an allowable value, stop the operation of the polishing device before polishing the next workpiece.

[0028] In one embodiment, the operation control unit is configured to calculate the difference between a plurality of distributions of the liquid amount determined at a plurality of points in time during the polishing of the workpiece, and if the difference in distribution is greater than an allowable value, to stop the operation of the polishing device before polishing the next workpiece.

[0029] In one embodiment, the operation control unit is configured to calculate the difference between a plurality of distributions of the liquid amount determined at a plurality of points in time during the polishing of the workpiece, and if the difference in distribution is greater than an allowable value, to change the pressure of the polishing head on the workpiece.

[0030] In one embodiment, the operation control unit is configured to change the polishing conditions for the workpiece in a direction that reduces the difference in distribution when the difference between the initial distribution and the current distribution of the liquid amount on the polishing surface is greater than a threshold.

[0031] In one embodiment, after changing the polishing conditions, the difference between the initial distribution of the liquid amount and the newly determined current distribution of the liquid amount is recalculated, and if the difference in distribution is greater than the threshold, the polishing operation of the polishing device is stopped before polishing the next workpiece.

[0032] In one embodiment, the operation control unit is configured to stop the polishing operation of the polishing device before polishing the next workpiece if the difference between the initial distribution and the current distribution of the amount of liquid on the polishing surface is greater than a threshold.

[0033] In one embodiment, the operation control unit is configured to determine that an abnormality has occurred in the polishing device when the distribution of the liquid amount on the polishing surface falls below a preset threshold distribution of the liquid amount.

[0034] In one embodiment, the liquid is one of a polishing liquid, pure water, a chemical solution, and colored water.

[0035] In one embodiment, a polishing method for polishing a workpiece is provided, comprising: a polishing table supporting a polishing pad; a polishing head rotating, and pressing the workpiece against the polishing surface of the polishing pad by the polishing head to polish the workpiece; and, before, during, or after polishing the workpiece, supplying a liquid onto the polishing surface, acquiring optical information included in light from a plurality of points on the polishing surface, and determining the distribution of the amount of liquid on the polishing surface from the optical information.

[0036] In one embodiment, the distribution of the liquid amount is determined by subtracting the first distribution, determined from the first optical information of the plurality of points on the polishing surface acquired before the supply of the liquid, from the second distribution, determined from the second optical information of the plurality of points on the polishing surface acquired at the time of the supply of the liquid.

[0037] In one embodiment, the process of acquiring the optical information is a process of acquiring the optical information at multiple points on the polishing surface at multiple points in time while polishing the workpiece while supplying a liquid onto the polishing surface, and the process of determining the distribution of the liquid amount is a process of acquiring the temporal trend of the distribution of the liquid amount on the polishing surface from the optical information at multiple points on the polishing surface acquired at the multiple points in time.

[0038] In one embodiment, the process of acquiring the optical information is a process of acquiring the optical information while supplying a liquid onto the polishing surface during an interval time before or after polishing the workpiece.

[0039] In one embodiment, the polishing method further comprises the steps of: acquiring initial optical information of a plurality of points on the polishing surface while supplying a liquid onto the polishing surface of the polishing pad in a non-polishing state; acquiring current optical information of a plurality of points on the polishing surface while supplying a liquid onto the polishing surface of the polishing pad in use for polishing; determining an initial distribution of the amount of liquid on the polishing surface from the initial optical information; determining a current distribution of the amount of liquid on the polishing surface from the current optical information; and calculating the difference between the initial distribution and the current distribution.

[0040] In one embodiment, the liquid supplied to the polishing surface of the polishing pad while acquiring the optical information is a liquid of a different type from the polishing liquid used for polishing the workpiece.

[0041] In one embodiment, the optical information is the amount of light from the polished surface.

[0042] In one embodiment, the optical information is the color distribution of the polished surface.

[0043] In one embodiment, the process of acquiring the optical information is a process of acquiring optical information of the plurality of points within a monitoring area located upstream of the polishing head in the rotational direction of the polishing table.

[0044] In one embodiment, the polishing method further comprises a process of calculating the difference between a plurality of distributions of the liquid amount determined at a plurality of points in time during the polishing of the workpiece, and if the difference in distribution is greater than an allowable value, changing the polishing conditions for the workpiece in a direction that reduces the difference in distribution.

[0045] In one embodiment, the polishing method further comprises a process of, after changing the polishing conditions, recalculating the difference between a plurality of distributions of the liquid amount determined at a plurality of points during the polishing of the workpiece, and if the difference in distribution is greater than an allowable value, stopping the operation of the polishing device before polishing the next workpiece.

[0046] In one embodiment, the polishing method further comprises a process of calculating the difference between a plurality of distributions of the liquid amount determined at a plurality of points in time during the polishing of the workpiece, and if the difference in distribution is greater than an allowable value, stopping the operation of the polishing device before polishing the next workpiece.

[0047] In one embodiment, the polishing method further comprises a process of calculating the difference between a plurality of distributions of the liquid amount determined at a plurality of points in time during the polishing of the workpiece, and, if the difference between the distributions is greater than an allowable value, changing the pressure of the polishing head on the workpiece.

[0048] In one embodiment, the polishing method further includes a process of changing the polishing conditions for the workpiece in a direction that reduces the difference in distribution when the difference between the initial distribution and the current distribution of the liquid amount on the polishing surface is greater than a threshold.

[0049] In one embodiment, the polishing method further comprises, after changing the polishing conditions, recalculating the difference between the initial distribution of the liquid amount on the polishing surface and the current distribution of the newly determined liquid amount, and if the difference in distribution is greater than the threshold, stopping the operation of the polishing device before polishing the next workpiece.

[0050] In one embodiment, the polishing method further includes a process of stopping the operation of the polishing device before polishing the next workpiece if the difference between the initial distribution and the current distribution of the liquid amount on the polishing surface is greater than a threshold.

[0051] In one embodiment, the polishing method further includes a process of determining that an abnormality has occurred in the polishing device when the distribution of the liquid amount falls below a preset critical distribution of the liquid amount.

[0052] In one embodiment, the liquid is one of a polishing liquid, pure water, a chemical solution, and colored water. Effects of the invention

[0053] According to the present invention, it is possible to monitor the distribution of liquid amounts, such as polishing liquid or chemical solution, on a polishing pad itself. Furthermore, by feeding the monitoring results back to the operation of a polishing device, it becomes possible to polish a workpiece, such as a wafer, under appropriate polishing conditions. Brief explanation of the drawing

[0054] FIG. 1 is a perspective view schematically illustrating one embodiment of a grinding device. Figure 2 is a cross-sectional view of the grinding head shown in Figure 1. Figure 3 is a plan view of the polishing pad, liquid supply device, and polishing head. Figure 4 is a diagram illustrating an example of a graph showing the distribution of polishing liquid volume. Figure 5 is a diagram illustrating an example of a graph showing the distribution of polishing liquid volume. Figures 6(a) and 6(b) are graphs illustrating the distribution of the amount of polishing liquid changed during the polishing of one wafer. Figure 7 is a graph showing the overall distribution of polishing liquid decreasing due to an abnormality in the polishing device. Figure 8 is a graph illustrating the change in the distribution of liquid volume when one of the multiple supply ports is blocked. Figure 9 is a graph showing the initial and current distribution of liquid volume. FIG. 10 is a graph illustrating an embodiment for determining whether the difference between the distributions of liquid amounts is within a predetermined range. Figure 11 is a graph illustrating the change in the distribution of liquid volume when one of the multiple supply ports is blocked. FIG. 12 (a) is a graph showing a first distribution obtained from first optical information acquired before the supply of liquid, FIG. 12 (b) is a graph showing a second distribution obtained from second optical information acquired at the time of supply of liquid, and FIG. 12 (c) is a graph showing a distribution of liquid amount obtained by subtracting the first distribution from the second distribution. Specific details for implementing the invention

[0055] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0056] FIG. 1 is a perspective view schematically illustrating one embodiment of a polishing device. As shown in FIG. 1, the polishing device comprises a polishing table (5) that supports a polishing pad (2) having a polishing surface (2a), a polishing head (7) that presses a wafer (W), which is a workpiece to be polished, against the polishing surface (2a), a liquid supply device (8) that supplies a liquid, such as a polishing liquid, to the polishing surface (2a), a liquid monitoring device (12) that acquires optical information included in light from the polishing surface (2a), an optical information analysis unit (13) that determines the distribution of the amount of liquid on the polishing surface (2a) from the optical information acquired by the liquid monitoring device (12), and an operation control unit (47) that controls the operation of the polishing device.

[0057] The polishing head (7) is configured to hold and support the wafer (W) on its lower surface by means of vacuum suction, etc. In this embodiment, the wafer (W) is circular. The workpiece to be polished is not limited to a wafer, provided it is a workpiece used in the manufacture of a semiconductor device. Other examples of the workpiece to be polished include a rectangular wafer, a substrate, a panel, etc.

[0058] The polishing device further comprises a support shaft (14), a polishing head oscillating arm (16) connected to the upper end of the support shaft (14) to oscillate the polishing head (7), a polishing head shaft (18) rotatably supported at the free end of the polishing head oscillating arm (16), and a polishing head rotation device (20) that rotates the polishing head (7) around its axis. The polishing head rotation device (20) is fixed to the polishing head oscillating arm (16) and is connected to the polishing head shaft (18) through a torque transmission mechanism (not shown) composed of a belt and a pulley. The polishing head (7) is connected to the lower end of the polishing head shaft (18). The polishing head rotation device (20) rotates the polishing head shaft (18) through the torque transmission mechanism, and the polishing head (7) rotates together with the polishing head shaft (18). In this way, the polishing head (7) is rotated by the polishing head rotation device (20) in the direction indicated by the arrow around its axis. An example of a grinding head rotation device (20) can be an electric motor.

[0059] The grinding head shaft (18) is movable up and down relative to the grinding head oscillating arm (16) by means of a lifting mechanism (not shown), and the grinding head (7) is movable up and down relative to the grinding head oscillating arm (16) by the up and down movement of the grinding head shaft (18).

[0060] The polishing device further comprises a polishing table rotation device (21) that rotates the polishing pad (2) and the polishing table (5) around their respective axes. The polishing table (5) is connected to the polishing table rotation device (21) via a table axis (5a). The polishing table (5) and the polishing pad (2) are configured to rotate around the table axis (5a) in the direction indicated by the arrow by the polishing table rotation device (21). The polishing pad (2) is attached to the upper surface of the polishing table (5). The upper surface of the polishing pad (2) forms a polishing surface (2a) for polishing a wafer (W). An electric motor may be cited as a specific example of the polishing table rotation device (21).

[0061] A liquid supply device (8) comprises a liquid nozzle (9) having a supply port (9a) at its tip, a nozzle oscillation mechanism (10) that oscillates the supply port (9a) of the liquid nozzle (9) in the radial direction of the polishing pad (2), a first liquid supply line (25) and a second liquid supply line (27) connected to the liquid nozzle (9), and a first flow control valve (31) and a second flow control valve (32) respectively installed in the first liquid supply line (25) and the second liquid supply line (27). The first liquid supply line (25) is a line for supplying a polishing liquid (typically a slurry) as a first liquid to the liquid nozzle (9), and the second liquid supply line (27) is a line for supplying a liquid of a different type from the first liquid (e.g., pure water, chemical solution, or colored water) to the liquid nozzle (9).

[0062] The first flow control valve (31) and the second flow control valve (32) are connected to an operation control unit (47), and the operation of the first flow control valve (31) and the second flow control valve (32) is controlled by the operation control unit (47). When the second flow control valve (32) is closed, if the operation control unit (47) opens the first flow control valve (31), a polishing liquid as a first liquid is supplied onto the polishing surface (2a) of the polishing pad (2). When the first flow control valve (31) is closed, if the operation control unit (47) opens the second flow control valve (32), a second liquid different from the polishing liquid is supplied onto the polishing surface (2a) of the polishing pad (2).

[0063] Polishing of the wafer (W) is performed as follows. While rotating the polishing head (7) and the polishing table (5) respectively, polishing liquid is supplied from the liquid nozzle (9) of the liquid supply device (8) onto the polishing surface (2a) of the polishing pad (2). An example of the polishing liquid supplied to the polishing pad (2) is a slurry containing abrasive particles. The polishing pad (2) rotates integrally with the polishing table (5) around its axis. The polishing head (7) is lowered to a predetermined polishing position by a lifting mechanism (not shown). Additionally, the polishing head (7) presses the wafer (W) against the polishing surface (2a) of the polishing pad (2) with a predetermined pressure at the polishing position. With the polishing liquid present on the polishing surface (2a) of the polishing pad (2), the wafer (W) is in sliding contact with the polishing surface (2a) of the polishing pad (2). The surface of the wafer (W) is polished by a combination of the chemical action of the polishing liquid supplied onto the polishing surface (2a) and the mechanical action of the abrasive particles contained in the polishing liquid and / or the polishing pad (2).

[0064] The optical information analysis unit (13) is equipped with a memory device (13a) in which a program is stored and an arithmetic unit (13b) that executes operations according to instructions included in the program. The memory device (13a) is equipped with a main memory device such as random access memory (RAM) and an auxiliary memory device such as a hard disk drive (HDD) or a solid-state drive (SSD). Examples of the arithmetic unit (13b) include a CPU (central processing unit) and a GPU (graphics processing unit). However, the specific configuration of the optical information analysis unit (13) is not limited to this embodiment.

[0065] The operation control unit (47) is equipped with a memory device (47a) in which a program is stored and an operation device (47b) that executes operations according to instructions included in the program. The memory device (47a) is equipped with a main memory device such as random access memory (RAM) and an auxiliary memory device such as a hard disk drive (HDD) or a solid-state drive (SSD). Examples of the operation device (47b) include a CPU (central processing unit) and a GPU (graphics processing unit). However, the specific configuration of the operation control unit (47) is not limited to this embodiment.

[0066] Each of the optical information analysis unit (13) and the operation control unit (47) may be composed of one computer or multiple computers. Alternatively, the optical information analysis unit (13) and the operation control unit (47) may be composed of one computer. The optical information analysis unit (13) and the operation control unit (47) do not need to be physically independent and may be virtually constructed by at least one computer.

[0067] A liquid monitoring device (12) is positioned above the polishing pad (2) and faces the polishing surface (2a). More specifically, the liquid monitoring device (12) faces at least a monitoring area (M) upstream of the polishing head (7) in the rotational direction of the polishing table (5) and the polishing pad (2), and is configured to acquire optical information included in light from the monitoring area (M). The monitoring area (M) extends in the radial direction of the polishing pad (2). In one embodiment, a plurality of monitoring areas may be set. These monitoring areas extend in the radial direction of the polishing pad (2) and are arranged along the circumferential direction of the polishing pad (2). One of the plurality of monitoring areas is located upstream of the polishing head (7), as indicated by the symbol M in FIG. 1.

[0068] The polishing device further comprises a light source (40) that irradiates light having one or more wavelengths within the range of 200 nm to 1100 nm onto the polishing surface (2a) of the polishing pad (2). The light source (40) is configured to emit at least visible light and, for example, is equipped with a light-emitting diode. It is preferable that the light source (40) uniformly illuminates the polishing surface (2a) of the polishing pad (2). For example, the light source (40) may have a plurality of light-emitting diodes or a light-dispersing plate. The light source (40) is positioned to irradiate uniform light toward at least a monitoring area (M).

[0069] FIG. 2 is a cross-sectional view of the polishing head (7) shown in FIG. 1. The polishing head (7) is equipped with a carrier (71) fixed to the polishing head shaft (18) and a retainer ring (72) positioned below the carrier (71). A flexible membrane (elastic film) (74) that contacts a wafer (W) is supported at the bottom of the carrier (71). Four pressure chambers (G1, G2, G3, G4) are formed between the membrane (74) and the carrier (71). The pressure chambers (G1, G2, G3, G4) are formed by the membrane (74) and the carrier (71). The central pressure chamber (G1) is circular, and the other pressure chambers (G2, G3, G4) are ring-shaped. These pressure chambers (G1, G2, G3, G4) are arranged concentrically. In one embodiment, five or more pressure chambers may be provided, or three or fewer pressure chambers may be provided.

[0070] In each pressure chamber (G1, G2, G3, G4), compressed gas, such as compressed air, is supplied from a gas supply source (77) through a fluid path (F1, F2, F3, F4). A wafer (W) is pressed against the polishing surface (2a) of a polishing pad (2) by a membrane (74). More specifically, the pressure of the compressed gas in the pressure chamber (G1, G2, G3, G4) acts on the wafer (W) through the membrane (74) to press the wafer (W) against the polishing surface (2a). The internal pressure of the pressure chamber (G1, G2, G3, G4) can be changed independently, thereby allowing the polishing pressure for the four corresponding regions of the wafer (W), namely the central region, the inner middle region, the outer middle region, and the peripheral region, to be adjusted independently.

[0071] Between the carrier (71) and the retainer ring (72), a ring-shaped rolling diaphragm (76) is disposed, and a pressure chamber (G5) is formed inside the rolling diaphragm (76). The pressure chamber (G5) is connected to the gas supply source (77) through a fluid path (F5). The gas supply source (77) supplies compressed gas into the pressure chamber (G5), and the compressed gas inside the pressure chamber (G5) presses the retainer ring (72) against the polishing surface (2a) of the polishing pad (2) through the rolling diaphragm (76).

[0072] The periphery of the wafer (W) and the lower surface of the membrane (74) (i.e., the wafer pressure surface) are surrounded by a retainer ring (72). During the polishing of the wafer (W), the retainer ring (72) presses the polishing surface (2a) of the polishing pad (2) from the outside of the wafer (W), preventing the wafer (W) from popping out of the polishing head (7) during polishing.

[0073] The fluid passages (F1, F2, F3, F4, F5) extend from the pressure chambers (G1, G2, G3, G4, G5) to the gas supply source (77). Pressure regulators (R1, R2, R3, R4, R5) are each installed in the fluid passages (F1, F2, F3, F4, F5). Compressed gas is supplied from the gas supply source (77) into the pressure chambers (G1 to G5) through the pressure regulators (R1 to R5) and the fluid passages (F1 to F5).

[0074] Pressure regulators (R1, R2, R3, R4, R5) are configured to control the pressure within pressure chambers (G1, G2, G3, G4, G5). Pressure regulators (R1, R2, R3, R4, R5) are connected to an operation control unit (47). The operation control unit (47) is configured to generate a target pressure value for each pressure chamber (G1 to G5). The operation control unit (47) sends the target pressure value to the pressure regulators (R1 to R5), and the pressure regulators (R1 to R5) operate so that the pressure within the pressure chambers (G1 to G5) matches the corresponding target pressure value.

[0075] FIG. 3 is a plan view of a polishing pad (2), a liquid supply device (8), and a polishing head (7). As shown in FIG. 3, polishing liquid is supplied from the liquid nozzle (9) of the liquid supply device (8) to an area near the center of the polishing surface (2a) of the polishing pad (2). The polishing liquid on the rotating polishing pad (2) spreads outward in the radial direction due to centrifugal force and comes into contact with the wafer (W) held and supported by the polishing head (7). Immediately after the supply of polishing liquid begins, the polishing liquid has not yet spread sufficiently over the polishing surface (2a). Therefore, typically, after the supply of polishing liquid begins and a preset time has elapsed, the polishing head (7) presses the wafer (W) against the polishing surface (2a).

[0076] The liquid monitoring device (12) is configured to acquire optical information included in light from the polishing surface (2a) of the polishing pad (2) and light from the liquid (e.g., polishing liquid) present on the polishing surface (2a). Specific examples of optical information include the color of the polishing surface (2a) and the liquid (i.e., color distribution on the polishing surface (2a)), the amount of light from the polishing surface (2a) and the liquid, etc. In this embodiment, the liquid monitoring device (12) is equipped with an image sensor that generates a color image. Examples of the image sensor include a CCD sensor, a COMS sensor, etc. The liquid monitoring device (12) is configured to generate a color image of a monitoring area (M) within the polishing surface (2a) and to acquire a color distribution as optical information appearing on the color image.

[0077] Typically, the polishing liquid and the polishing pad (2) have different colors. Therefore, the polishing liquid present on the polishing surface (2a) of the polishing pad (2) can be visually identified from the polishing surface (2a). The optical information analysis unit (13) is connected to the liquid monitoring device (12) and acquires a color image from the liquid monitoring device (12). Additionally, the optical information analysis unit (13) performs image processing on the color image to determine the distribution of the amount of polishing liquid present on the polishing surface (2a). More specifically, the optical information analysis unit (13) determines a liquid color index value representing the concentration of the color of the polishing liquid within the monitoring area (M) from the color image, and creates a polishing liquid amount distribution graph representing the amount of polishing liquid expressed by the liquid color index value at each location within the monitoring area (M).

[0078] FIG. 4 is a diagram illustrating an example of a graph showing the distribution of polishing liquid volume. In FIG. 4, the vertical axis represents the amount of liquid corresponding to the liquid color index value, and the horizontal axis represents a position within the monitoring area (M). In the example illustrated in FIG. 4, the position indicated by the horizontal axis is a radial position of the polishing pad (2). Since the liquid color index value changes depending on the amount of polishing liquid present on the polishing surface (2a), the liquid color index value corresponds to the amount of polishing liquid. The vertical axis of FIG. 4 represents the amount of polishing liquid expressed using the liquid color index value.

[0079] Liquid color index values ​​can be changed by the color model (or color space) that defines the color within a color image. Examples of color models used to quantitatively express color include RGB, CMY, CMYK, HSL, HSV, etc.

[0080] The liquid color index value may be a numerical value of only one of the multiple components defining each color model. For example, the RGB color model uses three components of R (red), G (green), and B (blue) as primary colors, but the liquid color index value may be represented by a numerical value of any one of these three components. In one example, each component of R (red), G (green), and B (blue) is expressed as a numerical value within the range of 0 to 255. By using only one component, it may be possible to detect the polishing liquid on the polishing surface (2a) with high precision.

[0081] In one embodiment, the optical information analysis unit (13) may determine the liquid color index value by using a composite value such as brightness or luminance in addition to each component of the color model (or color space). Brightness is the average of the maximum and minimum values ​​of each component of RGB, and luminance is the brightness perceived by the human eye, calculated as red component (R) × 0.21 + green component (G) × 0.72 + blue component (B) × 0.07. In this way, the optical information analysis unit (13) can determine the relative distribution of the polishing liquid on the polishing pad (2) by analyzing a color image that reflects the shade of the polishing liquid on the polishing pad (2). Additionally, the optical information analysis unit (13) may be configured to determine the distribution of the film thickness of the polishing liquid existing on the polishing surface (2a) from the color image by acquiring data in advance that indicates the relationship between the film thickness and color of the polishing liquid.

[0082] When the color of the polishing liquid is close to the color of the polishing pad (2), or when the polishing liquid is transparent, it may be difficult to determine the distribution of the amount of polishing liquid on the polishing pad (2) by processing a color image. Therefore, in one embodiment, the liquid monitoring device (12) has a light detection sensor that measures the amount of light, which is another example of optical information, instead of an image sensor that generates a color image. In one example, the light detection sensor is configured to measure the amount of light having one or more wavelengths within the range of 200 nm to 1100 nm. An example of a light detection sensor is a photodiode.

[0083] A liquid monitoring device (12) equipped with a light detection sensor measures the amount of light reflected from the polishing liquid within the monitoring area (M) and transmits the measured data to an optical information analysis unit (13). The optical information analysis unit (13) is configured to determine the distribution of the amount of polishing liquid on the polishing surface (2a) based on the measured data of the amount of light. In the area where polishing liquid exists on the polishing surface (2a) of the polishing pad (2), light is easily reflected by the polishing liquid, and consequently, the amount of light increases. Therefore, the optical information analysis unit (13) can determine the distribution of the amount of polishing liquid on the polishing surface (2a) based on the measured data of the amount of light obtained by the liquid monitoring device (12).

[0084] FIG. 5 is a diagram illustrating an example of a graph showing the distribution of polishing liquid volume. In FIG. 5, the vertical axis represents the amount of liquid corresponding to the amount of light reflected from the polishing liquid, and the horizontal axis represents a position within the monitoring area (M). In the example shown in FIG. 5, the position indicated by the horizontal axis is a radial position of the polishing pad (2). Since the amount of light reflected from the polishing liquid changes depending on the presence or absence of polishing liquid on the polishing surface (2a), the amount of light corresponds to the amount of polishing liquid present on the polishing surface (2a). The vertical axis of FIG. 5 represents the amount of polishing liquid expressed using the amount of light.

[0085] In one embodiment, the light detection sensor of the liquid monitoring device (12) may be an infrared sensor. The polishing surface (2a) and the polishing liquid emit infrared rays depending on their temperatures. During the polishing of the wafer (W), the temperature of the polishing surface (2a) of the polishing pad (2) rises due to sliding contact with the wafer (W). In contrast, the temperature of the polishing liquid is approximately room temperature. Therefore, there is a temperature difference between the polishing surface (2a) and the polishing liquid. The intensity of the infrared rays emitted from the polishing surface (2a) and the polishing liquid changes depending on these temperatures. The liquid monitoring device (12) equipped with an infrared sensor measures the intensity of the infrared rays within the monitoring area (M) and transmits the measurement data to the optical information analysis unit (13). The optical information analysis unit (13) determines the distribution of the amount of polishing liquid on the polishing surface (2a) based on the measurement data of the intensity of the infrared rays. The intensity of the infrared rays corresponds to the amount of polishing liquid present on the polishing surface (2a). In the case of using an infrared sensor, the light source (40) shown in FIG. 1 may be omitted.

[0086] When the color of the polishing liquid is close to the color of the polishing pad (2), or when the polishing liquid is transparent, the distribution of the amount of colored water on the polishing surface (2a) may be analyzed using colored water during the interval time before or after polishing of the wafer (W), such as during the idling of the polishing device. More specifically, during the interval time before or after polishing of the wafer (W), the operation control unit (47) closes the first flow control valve (31) shown in FIG. 1 and opens the second flow control valve (32) to supply colored water as the second liquid onto the polishing surface (2a) of the polishing pad (2) from the liquid supply device (8). Examples of colored water include black water containing carbon, etc. The operation control unit (47) issues a command to the liquid monitoring device (12) to acquire optical information contained in light from the polishing surface (2a) and the colored water. More specifically, the liquid monitoring device (12) generates a color image of the colored water on the polishing surface (2a) and sends the color image to the optical information analysis unit (13). The optical information analysis unit (13) can determine the distribution of the amount of colored water on the polishing surface (2a) by analyzing the color image. Additionally, depending on the color of the colored water and the color of the polishing surface (2a) of the polishing pad (2), there may be cases where the distribution of the obtained optical information (e.g., luminance value) and the distribution of the actual amount of liquid are inverted. In such cases, the distribution of the amount of liquid may be obtained by using data processing, such as inverting the luminance value.

[0087] As the liquid supplied during the interval time, pure water may be used instead of colored water. The operation control unit (47) closes the first flow control valve (31) shown in FIG. 1 and opens the second flow control valve (32) during the interval time before or after polishing the wafer (W), thereby supplying pure water as the second liquid from the liquid supply device (8) onto the polishing surface (2a) of the polishing pad (2). In this case, according to the other embodiment described above, the liquid monitoring device (12) measures the amount of light reflected from the pure water within the monitoring area (M), transmits the measurement data to the optical information analysis unit (13), and the optical information analysis unit (13) determines the distribution of the amount of pure water on the polishing surface (2a) based on the measurement data of the amount of light.

[0088] Additionally, as the liquid supplied during the interval time, a chemical solution may be used instead of colored water. In this case as well, the distribution of the chemical solution amount on the polished surface (2a) is obtained in the same manner as in the embodiment described above.

[0089] The polishing liquid used for polishing wafers is generally expensive. According to the above embodiment, which uses colored water, pure water, or a chemical solution instead of the polishing liquid, the cost of obtaining the distribution of liquid amount on the polishing surface (2a) can be reduced.

[0090] Depending on the polishing process, the polishing product may color the polishing surface (2a) of the polishing pad (2). For example, in copper polishing, copper ions in the polishing product may be mixed with the polishing liquid, thereby coloring the polishing surface (2a) of the polishing pad (2) and forming a color contrast with the liquid, such as the polishing liquid supplied from the liquid supply device (8). The liquid monitoring device (12) may generate a color image of the colored polishing surface (2a), and the optical information analysis unit (13) may determine the color distribution of the polishing surface (2a) from the color image and make this color distribution the distribution of the liquid amount on the polishing pad (2).

[0091] During the polishing of the wafer (W), it is desirable that the polishing liquid be uniformly distributed on the polishing surface (2a). This is because the polishing rate of the film on the wafer (W) can change depending on the amount of polishing liquid present on the polishing surface (2a). Therefore, the operation control unit (47) is configured to issue a command to the liquid monitoring device (12) to acquire optical information of the polishing surface (2a) at multiple points in time during the polishing of the wafer (W) (e.g., to generate multiple color images). The optical information analysis unit (13) is configured to acquire the temporal trend of the distribution of the polishing liquid amount by analyzing the optical information acquired at the multiple points in time.

[0092] If, during the polishing of the wafer (W), the distribution of the polishing liquid amount on the polishing surface (2a) changes, the operation control unit (47) may change the polishing conditions for the wafer (W) to restore the distribution of the polishing liquid amount to its original state. More specifically, the operation control unit (47) calculates the difference between multiple distributions of the polishing liquid amount determined at multiple points in time during the polishing of the wafer (W), and if the difference in distribution is greater than the allowable value, it determines that there is an abnormality in the distribution of the polishing liquid amount and changes the polishing conditions in a direction that reduces the difference in distribution. For example, the operation control unit (47) reduces the difference in distribution by changing at least one of the rotation speed of the polishing head (7), the rotation speed of the polishing table (5), the flow rate of the polishing liquid supplied from the liquid supply device (8), and the oscillation of the liquid nozzle (9). By doing this, unintended changes in the polishing rate or the polishing rate distribution of the wafer (W) can be prevented.

[0093] FIGS. 6(a) and FIGS. 6(b) are graphs illustrating the distribution of polishing liquid volume that changes during the polishing of a wafer (W). As shown in FIG. 6(a), during the polishing of the wafer (W), there may be cases where the current distribution of polishing liquid volume decreases from the distribution of polishing liquid volume at the start of polishing of the wafer (W). The operation control unit (47) calculates the difference in the distribution of these polishing liquids, and if the difference in distribution is greater than the allowable value, the operation control unit (47) changes the polishing conditions for the wafer (W) in a direction that reduces the difference, as shown in FIG. 6(b). For example, the operation control unit (47) increases the opening degree of the first flow control valve (31) to increase the flow rate of the polishing liquid supplied to the polishing surface (2a). If the distribution of the polishing liquid is skewed toward the inner or outer side of the polishing pad (2), the operation control unit (47) may issue a command to the polishing table rotation device (21) to increase or decrease the rotation speed of the polishing table (5).

[0094] In one embodiment, after a predetermined time has elapsed following the operation control unit (47) changing the polishing conditions of the polishing device, the optical information analysis unit (13) determines the distribution of the current polishing liquid amount during the polishing of the wafer (W), and the operation control unit (47) calculates the difference between the distribution of the polishing liquid amount at the start of polishing the wafer (W) and the distribution of the currently determined polishing liquid amount. If this difference in distribution is greater than the allowable value, the operation of the polishing device may be stopped before polishing the next wafer.

[0095] In addition, in one embodiment, the operation control unit (47) calculates the difference between the distributions of the amount of polishing liquid determined at multiple points in time during polishing of the wafer (W), and if the difference in distribution is greater than the allowable value, the operation of the polishing device may be stopped before polishing the next wafer without changing the polishing conditions of the wafer (W).

[0096] In addition, in one embodiment, the operation control unit (47) calculates the difference in the distribution of the polishing liquid amount determined at multiple points in time during the polishing of the wafer (W), and if the difference in distribution is greater than the allowable value, the pressure applied by the polishing head (7) to the wafer (W) may be changed. As shown in FIG. 6 (a), if the distribution of the polishing liquid amount decreases during the polishing of the wafer (W), a decrease in the polishing rate of the wafer (W) is expected due to the decrease in the amount of polishing liquid. Therefore, the operation control unit (47) increases the pressure applied by the polishing head (7) to the wafer (W) to compensate for the decrease in the polishing rate. Specifically, the operation control unit (47) issues a command to at least one of the pressure regulators (R1 to R4) shown in FIG. 2 to increase the pressure of at least one of the pressure chambers (G1 to G4) of the polishing head (7). As a result, the polishing head (7) can press the wafer (W) against the polishing pad (2) with a higher pressure, thereby maintaining the intended polishing rate.

[0097] Factors that cause a change in the distribution of polishing liquid on the polishing surface (2a) of the polishing pad (2) during polishing include a malfunction of the device or a change in the physical properties (viscosity, etc.) of the polishing liquid or the surface condition of the polishing pad (2) caused by a rise in the temperature of the polishing pad (2). In the case where the cause is a malfunction of the device, the malfunction of the device can be detected by monitoring the distribution of polishing liquid on the polishing pad (2).

[0098] In one embodiment, the operation control unit (47) may be configured to determine that an abnormality has occurred in the polishing device when the distribution of the liquid (e.g., polishing liquid, pure water, chemical solution, or colored water) falls below a preset threshold distribution. For example, as shown in FIG. 7, when the entire distribution of the liquid amount falls below a preset threshold distribution (or reference distribution), it is thought that the cause is a blockage of the liquid nozzle (9) or the first liquid supply line (25) (see FIG. 1). The operation control unit (47) may generate an alarm signal when the distribution of the liquid amount falls below a preset threshold distribution.

[0099] The liquid nozzle (9) shown in FIG. 1 has a single supply port (9a) at its tip, but in other embodiments, the liquid nozzle (9) may have multiple supply ports arranged along the radial direction of the polishing pad (2). In this case, the liquid nozzle (9) is likely to form a uniform film of liquid on the polishing surface (2a) of the polishing pad (2). However, if any one of the multiple supply ports is blocked, the distribution of the liquid volume is locally reduced. Meanwhile, the flow rate of the liquid caused by the blockage of one supply port does not change much overall. For this reason, it is difficult to detect the blockage of one supply port based on the change in flow rate. According to the above embodiment for monitoring the distribution of the liquid volume, as shown in FIG. 8, when the distribution of the liquid volume falls below a critical distribution, the operation control unit (47) determines the occurrence of an abnormality, so that partial blockage of the liquid nozzle (9) can be detected.

[0100] Typically, a plurality of grooves are formed on the polishing surface (2a) of the polishing pad (2) to control the flow of the polishing liquid. As the polishing pad (2) is polished, it gradually wears down, and the depth of the grooves on the polishing surface (2a) gradually becomes shallower. As a result, even if the flow rate of the polishing liquid supplied from the liquid supply device (8) does not change, the distribution of the amount of polishing liquid on the polishing surface (2a) may change.

[0101] Therefore, in order to investigate the temporal change in the distribution of the polishing liquid amount, in the embodiment described below, the liquid amount distribution when the polishing pad (2) is not in use and the liquid amount distribution when the polishing pad (2) is in use are compared. More specifically, the operation control unit (47) is configured to issue a command to the liquid monitoring device (12) to acquire the initial optical information of the polishing surface (2a) of the polishing pad (2) in a non-polishing state and the current optical information of the polishing surface (2a) of the polishing pad (2) after polishing use. The polishing pad (2) in a non-polishing state is a new polishing pad that is not being used for polishing a wafer.

[0102] The liquid used is any of polishing liquid, pure water, chemical liquid, or colored water; however, since polishing liquid is generally expensive, it is preferable that the liquid used be any of pure water, chemical liquid, or colored water. Specific examples of optical information of the polishing surface (2a) include the color distribution on the polishing surface (2a), the amount of light from the polishing surface (2a) and the liquid, etc. As described above, the liquid monitoring device (12) is equipped with an image sensor, a light detection sensor, an infrared sensor, etc. For example, the liquid monitoring device (12) generates an initial color image of the liquid on the polishing surface (2a) of the polishing pad (2) in a non-polishing state, and generates an immediate color image of the liquid on the polishing surface (2a) of the polishing pad (2) in use. Alternatively, the liquid monitoring device (12) measures the initial amount of light from the liquid on the polishing surface (2a) of the polishing pad (2) in a non-polishing state, and measures the immediate amount of light from the liquid on the polishing surface (2a) of the polishing pad (2) in use.

[0103] The optical information analysis unit (13) determines the initial distribution of liquid amount on the polishing surface (2a) from the initial optical information (e.g., an initial color image or measurement data of the initial amount of light) and determines the current distribution of liquid amount on the polishing surface (2a) from the current optical information (e.g., a color image of the nearest point or measurement data of the amount of light). FIG. 9 is a graph showing the initial distribution of liquid amount on the polishing surface (2a) and the current distribution of liquid amount on the polishing surface (2a). As shown in FIG. 9, the distribution of liquid amount on the polishing surface (2a) changes over time due to wear of the polishing pad (2).

[0104] The operation control unit (47) receives data on the initial distribution and current distribution of liquid on the polishing surface (2a) from the optical information analysis unit (13) and stores it in the memory device (47a). The operation control unit (47) is configured to determine the state of the polishing pad (2) from the difference between the initial distribution and the current distribution of liquid on the polishing surface (2a). More specifically, the operation control unit (47) calculates the difference between the initial distribution and the current distribution of liquid on the polishing surface (2a), and if this difference in distribution is greater than a threshold, it is configured to generate an alarm signal indicating the depletion of the polishing pad (2).

[0105] The operation control unit (47) may be configured to change the polishing conditions for the wafer in a direction that reduces the difference in distribution when the difference between the initial distribution and the current distribution of the liquid amount on the polishing surface (2a) is greater than a threshold. More specifically, the operation control unit (47) reduces the difference in distribution by changing at least one of the rotational speed of the polishing head (7), the rotational speed of the polishing table (5), the flow rate of the liquid supplied from the liquid supply device (8), and the oscillation of the liquid nozzle (9). By doing so, unintended changes in the polishing rate or polishing rate distribution of the wafer can be prevented.

[0106] In one embodiment, after a predetermined time has elapsed since the operation control unit (47) changed the polishing conditions, the optical information analysis unit (13) determines the current distribution of liquid amount on the polishing surface (2a), and the operation control unit (47) calculates the difference between the initial distribution of liquid amount and the current distribution of liquid amount determined again, and if this difference in distribution is greater than the threshold, the operation of the polishing device may be stopped before polishing the next wafer.

[0107] In addition, in one embodiment, the operation control unit (47) may stop the operation of the polishing device before polishing the next wafer without changing the polishing conditions of the wafer when the difference between the initial distribution and the current distribution of the liquid amount on the polishing surface (2a) is greater than the threshold.

[0108] Additionally, in one embodiment, the operation control unit (47) may change the pressure applied by the polishing head (7) to the wafer when the difference between the initial distribution and the current distribution of the liquid amount on the polishing surface (2a) is greater than the threshold. As shown in FIG. 9, as the polishing pad (2) deteriorates, the amount of polishing liquid on the polishing surface (2a) of the polishing pad (2) decreases, and a decrease in the polishing rate of the wafer is expected due to the decrease in the amount of polishing liquid. Therefore, the operation control unit (47) increases the pressure applied by the polishing head (7) to the wafer to compensate for the decrease in the polishing rate. Specifically, the operation control unit (47) issues a command to at least one of the pressure regulators (R1 to R4) shown in FIG. 2 to increase the pressure of at least one of the pressure chambers (G1 to G4) of the polishing head (7). As a result, the polishing head (7) can apply pressure to the wafer against the polishing pad (2) with a higher pressure, thereby maintaining the intended polishing rate.

[0109] The allowable value and the threshold, which are compared with the difference between the distribution of liquid amount on the polishing surface (2a), may be determined from the difference between the distribution of liquid amount during normal conditions and the distribution when the distribution of liquid amount during normal conditions changes by a predetermined ratio, for example, 10%. The distribution of liquid amount during normal conditions may be, for example, the distribution of liquid amount when the polishing rate profile of the wafer is normal.

[0110] Due to manufacturing variations of the polishing pad (2), the distribution of the liquid volume during normal operation may also change. In such cases, data of multiple liquid volume distributions during normal operation in the past may be accumulated in the memory device (47a) of the operation control unit (47), and as shown in FIG. 10, the operation control unit (47) may determine whether the difference is within a defined range from the data.

[0111] The allowable value and the threshold, which are compared with the difference between the distribution of liquid amounts on the polishing surface (2a), may be automatically determined by artificial intelligence (AI). For example, they may be accumulated in the memory device (47a) of the operation control unit (47) by combining liquid amount distribution data with information on consumable materials such as polishing pads or liquids, or information on the occurrence of polishing abnormalities. Furthermore, by machine learning the trend of the distribution of liquid amounts for each combination of polishing pads and liquids using artificial intelligence (AI), etc., and inputting the consumable material information into the operation control unit (47), it becomes possible to automatically set the allowable value and the threshold.

[0112] In addition, as illustrated in FIG. 11, for example, when an abnormality in the liquid volume distribution is localized and small, such an abnormality may not be correctly detected. In such cases, high-precision determination becomes possible by determining normality or abnormality based on the shape of the liquid volume distribution rather than the allowable value or threshold. Specifically, the liquid volume distribution at the time of an abnormality is recognized by the operation control unit (47) as abnormality data through machine learning, so that when a similar liquid volume distribution is detected, it is determined to be abnormal.

[0113] In the embodiment described so far, the optical information analysis unit (13) determines the distribution of liquid amount on the polishing surface (2a) of the polishing pad (2) from optical information (e.g., color in a color image, measurement data of light amount, etc.) obtained from the liquid monitoring device (12). However, above the polishing pad (2), there is a light-blocking material, such as a dresser for dressing (regenerating) the polishing surface (2a) of the polishing pad (2) or an atomizer for cleaning the polishing surface (2a), although this is not shown. Also, depending on the position of the light source (40), there may be variations in the amount of light reflected by the liquid on the polishing pad (2). Additionally, there is the color of the polishing pad (2) itself and variations therein. The presence of such light-blocking material, the light source (40), and the influence of the color and variations of the polishing pad (2) hinder the optical information analysis unit (13) from determining the accurate distribution of the liquid on the polishing surface (2a).

[0114] Therefore, in the embodiment described below, the operation control unit (47) is configured to issue a command to the liquid monitoring device (12) before the supply of liquid to acquire first optical information included in the light from the polishing surface (2a) of the polishing pad (2), and also to issue a command to the liquid monitoring device (12) when the liquid is supplied to acquire second optical information included in the light from the polishing surface (2a). In addition, the optical information analysis unit (13) is configured to determine the distribution of the liquid amount by determining a first distribution from the first optical information, determining a second distribution from the second optical information, and subtracting the first distribution from the second distribution.

[0115] FIG. 12(a) is a graph showing a first distribution obtained from first optical information of a polished surface (2a) obtained by a liquid monitoring device (12) before the supply of liquid, FIG. 12(b) is a graph showing a second distribution obtained from second optical information of a polished surface (2a) obtained by a liquid monitoring device (12) when the liquid is supplied, and FIG. 12(c) is a graph showing a distribution of liquid amount obtained by subtracting the first distribution from the second distribution. As shown in FIG. 12(a) and FIG. 12(b), noise caused by a light-blocking material such as a dresser appears in the first distribution and the second distribution. Therefore, by subtracting the first distribution from the second distribution, a distribution of liquid amount with noise removed is obtained as shown in FIG. 12(c).

[0116] The above-described embodiments are described for the purpose of enabling a person skilled in the art to practice the present invention. Various modifications of the above embodiments are naturally achievable by those skilled in the art, and the technical concept of the present invention may be applied to other embodiments. Accordingly, the present invention is not limited to the described embodiments but is interpreted within the broadest scope according to the technical concept defined by the claims. Explanation of the symbols

[0117] 2: Polishing pad 2a: Polished surface 5: Grinding table 5a: Table axis 7: Grinding head 8: Liquid supply device 9: Liquid nozzle 9a: Supply port 10: Nozzle oscillation mechanism 12: Liquid monitoring device 13: Optical Information Interpretation Unit 14: Support axis 16: Grinding head oscillating arm 18: Grinding head shaft 20: Grinding head rotation device 21: Grinding table rotary device 25: 1st liquid supply line 27: Second liquid supply line 31: First flow control valve 32: Second flow control valve 40: Light source 47: Operation control unit 71: Carrier 72: Retainer ring 74: Membrane (Elastic membrane) 76: Rolling diaphragm W: Wafer (workpiece) M: Monitoring area F1, F2, F3, F4, F5: Fluid G1, G2, G3, G4, G5: Pressure chambers R1, R2, R3, R4, R5: Pressure regulators

Claims

Claim 1 A polishing device for polishing a workpiece, comprising: a polishing table that supports a polishing pad; a polishing head that presses the workpiece against the polishing surface of the polishing pad; a liquid supply device that supplies liquid onto the polishing surface; a polishing table rotation device that rotates the polishing table; a polishing head rotation device that rotates the polishing head; a liquid monitoring device that acquires optical information included in light from multiple points on the polishing surface; an optical information analysis unit that determines the distribution of the liquid amount on the polishing surface from the optical information; and an operation control unit that controls the operation of the polishing device. The operation control unit is configured to issue a command to the liquid monitoring device before the supply of the liquid to acquire first optical information of multiple points on the polishing surface, and to issue a command to the liquid monitoring device when the liquid is supplied to acquire second optical information of multiple points on the polishing surface. The optical information analysis unit is configured to determine a first distribution from the first optical information, determine a second distribution from the second optical information, and determine the distribution of the liquid amount by subtracting the first distribution from the second distribution. Claim 2 A polishing device according to claim 1, wherein the operation control unit is configured to issue a command to the liquid monitoring device to acquire optical information of multiple points on the polishing surface at multiple points in time during polishing of the workpiece, and the optical information analysis unit is configured to acquire a temporal trend of the distribution of the liquid amount on the polishing surface from the optical information of multiple points on the polishing surface acquired at the multiple points in time. Claim 3 A polishing device according to claim 1, wherein the operation control unit is configured to issue a command to the liquid monitoring device to acquire the optical information during the interval time before or after polishing the workpiece. Claim 4 A polishing device according to paragraph 3, wherein the operation control unit is configured to issue a command to the liquid supply device to supply the liquid of a different type from the polishing liquid used for polishing the workpiece onto the polishing surface of the polishing pad while the liquid monitoring device is acquiring the optical information. Claim 5 A polishing apparatus according to any one of claims 1 to 4, further comprising a light source that irradiates the polishing surface with light having one or more wavelengths within the range of 200 nm to 1100 nm. Claim 6 A polishing device according to any one of claims 1 to 4, wherein the liquid monitoring device has a light detection sensor for measuring the amount of light having one or more wavelengths within the range of 200 nm to 1100 nm. Claim 7 A polishing device according to claim 6, wherein the optical information analysis unit is configured to determine the distribution of the liquid amount on the polishing surface based on the light amount measurement data. Claim 8 In any one of claims 1 to 4, the liquid monitoring device is a polishing device having an image sensor that generates a color image. Claim 9 A polishing device according to claim 8, wherein the optical information analysis unit is configured to determine the distribution of the liquid amount on the polishing surface by analyzing the color distribution as the optical information appearing on the color image. Claim 10 A polishing device according to any one of claims 1 to 4, wherein the liquid monitoring device is arranged to acquire optical information of the plurality of points within a monitoring area located upstream of the polishing head in the rotational direction of the polishing table. Claim 11 A polishing device according to paragraph 2, wherein the operation control unit calculates the difference between a plurality of distributions of liquid amounts on the polishing surface determined at a plurality of points in time during the polishing of the workpiece, and if the difference between the distributions is greater than an allowable value, changes the polishing conditions for the workpiece in a direction in which the difference between the distributions becomes smaller. Claim 12 A polishing device according to claim 11, wherein the operation control unit is configured to recalculate the difference between a plurality of distributions of liquid amounts determined during polishing of the workpiece after changing the polishing conditions, and if the difference between the distributions is greater than an allowable value, stop the operation of the polishing device before polishing the next workpiece. Claim 13 A polishing device according to paragraph 2, wherein the operation control unit calculates the difference between a plurality of distributions of liquid amounts determined at a plurality of points in time during the polishing of the workpiece, and if the difference between the distributions is greater than an allowable value, the operation of the polishing device is stopped before polishing the next workpiece. Claim 14 A polishing device according to paragraph 2, wherein the operation control unit calculates the difference between a plurality of distributions of liquid amounts determined at a plurality of points in time during the polishing of the workpiece, and if the difference between the distributions is greater than an allowable value, the polishing head changes the pressure applied to the workpiece. Claim 15 A polishing device for polishing a workpiece, comprising: a polishing table that supports a polishing pad; a polishing head that presses the workpiece against the polishing surface of the polishing pad; a liquid supply device that supplies liquid onto the polishing surface; a polishing table rotation device that rotates the polishing table; a polishing head rotation device that rotates the polishing head; a liquid monitoring device that acquires optical information included in light from multiple points on the polishing surface; an optical information analysis unit that determines the distribution of the liquid amount on the polishing surface from the optical information; and an operation control unit that controls the operation of the polishing device. The operation control unit is configured to issue a command to the liquid monitoring device to acquire initial optical information from multiple points on the polishing surface of the polishing pad in a non-polishing state and current optical information from multiple points on the polishing surface of the polishing pad in use for polishing. The optical information analysis unit determines the initial distribution of the liquid amount from the initial optical information and determines the current distribution of the liquid amount on the polishing surface from the current optical information. The operation control unit is configured to calculate the difference between the initial distribution and the current distribution. Claim 16 A polishing device according to claim 15, wherein the operation control unit is configured to change the polishing conditions for the workpiece in a direction that reduces the difference in distribution when the difference between the initial distribution and the current distribution of the liquid amount on the polishing surface is greater than a threshold. Claim 17 A polishing device according to claim 16, configured such that after changing the polishing conditions, the difference between the initial distribution of the liquid amount and the newly determined current distribution of the liquid amount is recalculated, and if the difference in the distribution is greater than the threshold, the polishing operation of the polishing device is stopped before polishing the next workpiece. Claim 18 A polishing device according to claim 15, wherein the operation control unit is configured to stop the polishing operation of the polishing device before polishing the next workpiece when the difference between the initial distribution and the current distribution of the liquid amount on the polishing surface is greater than a threshold. Claim 19 A polishing device according to claim 15, wherein the operation control unit is configured to determine that an abnormality has occurred in the polishing device when the distribution of the liquid amount on the polishing surface falls below a preset threshold distribution of the liquid amount. Claim 20 In paragraph 15, the above liquid is a polishing device, which is one of a polishing liquid, pure water, a chemical solution, and colored water. Claim 21 A polishing method for polishing a workpiece, comprising: a polishing table that supports a polishing pad; a polishing head that rotates and presses the workpiece against the polishing surface of the polishing pad by means of the polishing head to polish the workpiece; and, before, during, or after polishing the workpiece, supplying a liquid onto the polishing surface, acquiring optical information included in light from multiple points on the polishing surface, and determining a distribution of liquid amount on the polishing surface from the optical information, wherein the distribution of liquid amount is determined by subtracting a first distribution determined from first optical information of multiple points on the polishing surface acquired before the supply of the liquid from a second distribution determined from second optical information of multiple points on the polishing surface acquired at the time of the supply of the liquid. Claim 22 A polishing method according to claim 21, wherein the process of acquiring the optical information is a process of acquiring the optical information of multiple points on the polishing surface at multiple points in time while polishing the workpiece while supplying a liquid on the polishing surface, and the process of determining the distribution of the liquid amount is a process of acquiring the temporal trend of the distribution of the liquid amount on the polishing surface from the optical information of multiple points on the polishing surface acquired at the multiple points in time. Claim 23 In claim 21, the process of acquiring the optical information is a polishing method in which, during an interval time before or after polishing of the workpiece, a liquid is supplied onto the polishing surface to acquire the optical information. Claim 24 A polishing method according to claim 23, wherein the liquid supplied to the polishing surface of the polishing pad while acquiring the optical information is a liquid of a different type from the polishing liquid used for polishing the workpiece. Claim 25 A polishing method according to any one of claims 21 to 24, wherein the optical information is the amount of light from the polished surface. Claim 26 A polishing method according to any one of claims 21 to 24, wherein the optical information is the color distribution of the polished surface. Claim 27 A polishing method according to any one of claims 21 to 24, wherein the process of acquiring the optical information is a process of acquiring optical information of the plurality of points within a monitoring area located upstream of the polishing head in the rotational direction of the polishing table. Claim 28 A polishing method according to claim 22, further comprising a process of calculating the difference between multiple distributions of liquid amounts determined at multiple points in time during polishing of the workpiece, and, if the difference between the distributions is greater than an allowable value, changing the polishing conditions for the workpiece in a direction that reduces the difference between the distributions. Claim 29 A polishing method according to claim 28, further comprising the process of, after changing the polishing conditions, recalculating the difference between the distributions of the liquid amount determined at multiple points during the polishing of the workpiece, and if the difference between the distributions is greater than an allowable value, stopping the operation of the polishing device before polishing the next workpiece. Claim 30 A polishing method according to claim 22, further comprising the process of calculating the difference between a plurality of distributions of the liquid amount determined at a plurality of points in time during polishing of the workpiece, and stopping the operation of the polishing device before polishing the next workpiece if the difference between the distributions is greater than an allowable value. Claim 31 A polishing method according to claim 22, further comprising a process of calculating the difference between a plurality of distributions of the liquid amount determined at a plurality of points in time during polishing of the workpiece, and changing the pressure of the polishing head on the workpiece when the difference between the distributions is greater than an allowable value. Claim 32 A polishing method for polishing a workpiece, wherein the method comprises: supplying a liquid onto a polishing surface of a polishing pad that is not in use for polishing, acquiring initial optical information of multiple points on the polishing surface, determining an initial distribution of the amount of liquid on the polishing surface from the initial optical information, polishing a workpiece by pressing it against the polishing surface of the polishing pad by means of a polishing head while rotating a polishing table that supports the polishing pad, and polishing the workpiece by supplying a liquid onto a polishing surface of a polishing pad that is in use for polishing, acquiring current optical information of multiple points on the polishing surface, determining a current distribution of the amount of liquid on the polishing surface from the current optical information, and calculating the difference between the initial distribution and the current distribution. Claim 33 A polishing method according to claim 32, wherein if the difference between the initial distribution and the current distribution of the liquid amount on the polishing surface is greater than a threshold, the polishing conditions for the workpiece are further modified in a direction in which the difference in distribution becomes smaller. Claim 34 A polishing method according to claim 33, further comprising the process of, after changing the polishing conditions, recalculating the difference between the initial distribution of the liquid amount on the polishing surface and the current distribution of the newly determined liquid amount, and if the difference in distribution is greater than the threshold, stopping the operation of the polishing device before polishing the next workpiece. Claim 35 A polishing method according to claim 32, further comprising a process of stopping the operation of a polishing device before polishing the next workpiece when the difference between the initial distribution and the current distribution of the liquid amount on the polishing surface is greater than a threshold. Claim 36 A polishing method comprising, in any one of claims 32 to 35, a process for determining that an abnormality has occurred in the polishing device when the distribution of the liquid amount falls below a preset critical distribution of the liquid amount. Claim 37 A polishing method according to any one of paragraphs 32 to 35, wherein the liquid is one of a polishing liquid, pure water, a chemical solution, and a colored water. Claim 38 delete Claim 39 delete

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