Method of raising polishing head after polishing of workpiece, polishing apparatus for workpiece, and computer-readable storage medium storing program

Abstract

This invention provides a method for raising a grinding head after workpiece grinding, a workpiece grinding apparatus, and a computer-readable recording medium containing a program. This method of raising the grinding head prevents the workpiece from bending due to contact with the retaining ring and prevents excessive stress on the workpiece when the grinding head is raised from the grinding pad after workpiece grinding is completed. The method involves rotating the grinding head (7) and grinding pad (2) while pressing the workpiece (W) against the grinding pad (2) to grind the workpiece (W). The rotation of the grinding pad (2) and grinding head (7) stops, and the retaining ring (48) of the grinding head (7) rises relative to the workpiece (W), thereby separating the retaining ring (48) from the grinding pad (2) and moving the retaining ring (48) to a position higher than the workpiece (W). Then, the grinding head (7) is raised while the workpiece (W) is held on the grinding head (7).

Description

A method for raising the grinding head after workpiece grinding, a workpiece grinding apparatus, and a computer-readable recording medium containing the recorded program. This invention relates to a technique for raising the grinding head together with the workpiece after grinding to reduce the stress of the workpiece used in the manufacture of semiconductor devices such as wafers, substrates, and panels. Chemical mechanical polishing (CMP) is a process that involves simultaneously polishing materials containing silicon dioxide (SiO2) with silicon dioxide. 2) A technique for grinding by supplying abrasive slurry of equal abrasive particles to the grinding surface of the grinding pad, thereby causing the workpiece to slide into contact with the grinding surface. As shown in Figure 13, a grinding apparatus for CMP includes: a grinding table 501 that supports a grinding pad 500; a grinding head 505 for holding the workpiece W; and a grinding slurry nozzle 508 that supplies grinding slurry to the grinding pad 500. The grinding of workpiece W using such a grinding apparatus is performed as follows: While the grinding table 501 and the grinding pad 500 are rotated together, grinding fluid is supplied to the grinding pad 500 from the grinding fluid nozzle 508. The grinding head 505 rotates the workpiece W and presses it against the grinding pad 500. The workpiece W slides in contact with the grinding pad 500 in the presence of the grinding fluid, and the surface of the workpiece W is flattened by a combination of the chemical action of the grinding fluid, the abrasive particles contained in the grinding fluid, and the mechanical action of the grinding pad 500. During the grinding of workpiece W, the surface of workpiece W slides in contact with the rotating grinding pad 500, thus friction is applied to workpiece W. Therefore, in order to prevent workpiece W from detaching from the grinding head 505 during grinding, the grinding head 505 is equipped with a retaining ring 510. This retaining ring 510 is configured to surround workpiece W, and during grinding, the retaining ring 510 rotates while pressing against the grinding pad 500 on the outside of workpiece W. Figure 14 is a cross-sectional view showing a portion of the grinding head 505 shown in Figure 13. As shown in Figure 14, the grinding head 505 has an annular elastic membrane 512 for pressing a retaining ring 510 against a grinding pad 500. A pressure chamber 513 is formed inside the elastic membrane 512. When pressurized gas (e.g., pressurized air) is supplied into the pressure chamber 513, the elastic membrane 512, subjected to the fluid pressure within the pressure chamber 513, presses the retaining ring 510 against the grinding pad 500. Therefore, during the grinding of the workpiece W, the retaining ring 510 prevents the workpiece W from flying out of the grinding head 505. The grinding head 505 also has an elastic diaphragm 514 for pressing the workpiece W against the grinding pad 500. A pressure chamber 515 is formed inside the elastic diaphragm 514. When pressurized gas (e.g., pressurized air) is supplied into the pressure chamber 515, the elastic diaphragm 514, under the fluid pressure within the pressure chamber 515, presses the workpiece W against the grinding pad 500. Therefore, the workpiece W slides in contact with the grinding pad 500 while the grinding fluid is present on the grinding pad 500. Both elastic membranes 512 and 514 are fixed to the carrier 517 of the grinding head 505. The retaining ring 510 is configured to move up and down relative to the carrier 517 and the elastic membrane 514 so that it can press against the grinding pad 500 independently of the workpiece W. After grinding the workpiece W, as shown in Figure 15, a negative pressure is formed in the pressure chamber 515, causing the workpiece W to adhere to the elastic membrane 514. While the workpiece W is adhered to the elastic membrane 514, it is slightly lifted. When the surface tension of the liquid between the workpiece W and the grinding pad 500 is high, sometimes the lifting of the workpiece W from the grinding pad 500 fails. Therefore, to reduce the surface tension acting between the workpiece W and the grinding pad 500, the grinding head 505 and the grinding pad 500 are rotated separately while the workpiece W is adhered to the elastic membrane 514. Then, the grinding head 505 and the workpiece W are raised together, and subsequently, the grinding head 505 and the workpiece W are moved together to a predetermined workpiece contact position. [Prior Art Documents] [Patent Documents] [Patent Document 1] Japanese Patent Application Publication No. 2009-178800 (The problem that the invention aims to solve) As the grinding head 505 rises, in order to prevent the workpiece W on the rotating grinding pad 500 from flying off the grinding head 505, the retaining ring 510 presses against the grinding pad 500. Therefore, as shown in FIG16, the carrier 517 of the grinding head 505 and the workpiece W rise and separate from the grinding pad 500, while the lower surface of the retaining ring 510 remains in contact with the grinding pad 500. However, if the workpiece W attempts to rise while in contact with the inner surface of the retaining ring 510, the portion of the workpiece W in contact with the inner surface of the retaining ring 510 will remain on the abrasive pad 500. Therefore, the workpiece W bends downwards, sometimes generating excessive stress. If this stress is too high, the workpiece W may break. In particular, as shown in FIG17, when wear grooves 510a formed on the inner surface of the retaining ring 510 due to contact with the workpiece W are formed, it is easier for the workpiece W to hook, thus making it prone to bending downwards significantly, resulting in a higher likelihood of breakage. Therefore, the present invention provides a method for raising a grinding head, which, when the grinding head is raised from the grinding pad after grinding of the workpiece, prevents the workpiece from bending by avoiding contact with the inner surface of the retaining ring, thereby preventing excessive stress on the workpiece. Furthermore, the present invention provides a grinding apparatus for a workpiece capable of performing such a method. Moreover, the present invention provides a computer-readable recording medium containing a program for performing such a method. (Means to Solve the Problem) In one embodiment, a method is provided for raising a grinding head after workpiece grinding, wherein the grinding head and grinding pad are rotated while the workpiece is pressed against the grinding pad and ground, the rotation of the grinding pad and the grinding head is stopped, and the retaining ring of the grinding head is raised relative to the workpiece, thereby separating the retaining ring from the grinding pad and moving the retaining ring to a position higher than the workpiece, and then the grinding head is raised while the workpiece is held on the grinding head. In one embodiment, the method further includes the step of holding the workpiece with the grinding head after grinding and before raising the grinding head. In one embodiment, the step of raising the holding ring to a position higher than the workpiece is performed before or simultaneously with holding the workpiece with the grinding head. In one embodiment, the step of holding the workpiece with the grinding head is performed while directly supplying fluid between the workpiece and the grinding pad. In one embodiment, the grinding head has an elastic membrane forming a plurality of pressure chambers for pressing the workpiece against the grinding pad, and the step of holding the workpiece with the grinding head is achieved by creating a negative pressure in the outer pressure chamber of the plurality of pressure chambers and then creating a negative pressure in the inner pressure chamber, thereby holding the workpiece with the grinding head. In one embodiment, the step of holding the workpiece with the grinding head is performed before stopping the rotation of the grinding pad and the grinding head. In one embodiment, the process of raising the grinding head includes the following steps: raising the grinding head at a first speed until the entire workpiece leaves the grinding pad; and raising the grinding head at a second speed higher than the first speed after the entire workpiece leaves the grinding pad. In one embodiment, a grinding apparatus for a workpiece is provided, comprising: a grinding table for supporting a grinding pad; a grinding table rotation device for rotating the grinding table and the grinding pad together; a grinding head for pressing the workpiece against the grinding pad to grind the workpiece; a grinding head pressure control device for controlling the pressure inside the grinding head; a grinding head rotation device for rotating the grinding head; a grinding head lifting device for moving the grinding head up and down relative to the grinding table; and an action control unit for controlling the grinding table rotation device and the grinding pad. The operation of the head pressure control device, the grinding head rotation device, and the grinding head lifting device, wherein the grinding head has a retaining ring surrounding the workpiece, the operation control unit is configured to, after grinding the workpiece, issue commands to the grinding table rotation device and the grinding head rotation device to stop the rotation of the grinding pad and the grinding head, issue commands to the grinding head pressure control device to raise the retaining ring relative to the workpiece, thereby separating the retaining ring from the grinding pad and moving the retaining ring to a position higher than the workpiece, and then issue commands to the grinding head lifting device to raise the grinding head while the workpiece is held on the grinding head. In one embodiment, the motion control unit is configured to instruct the grinding head pressure control device to hold the workpiece using the grinding head after it has been ground and before it rises. In another embodiment, the motion control unit is configured to instruct the grinding head pressure control device to raise the retaining ring to a position higher than the workpiece before or simultaneously with holding the workpiece using the grinding head. In one embodiment, the grinding apparatus further includes a fluid supply system for supplying fluid between the workpiece and the grinding pad; the motion control unit is configured to instruct the fluid supply system to hold the workpiece using the grinding head while directly supplying fluid between the workpiece and the grinding pad. In one embodiment, the grinding head has an elastic membrane forming a plurality of pressure chambers for pressing the workpiece against the grinding pad; the motion control unit is configured to instruct the grinding head pressure control device to create a negative pressure in the outer pressure chamber of the plurality of pressure chambers and then create a negative pressure in the inner pressure chamber, thereby holding the workpiece using the grinding head. In one embodiment, the motion control unit is configured to hold the workpiece with the grinding head until the rotation of the grinding pad and the grinding head stops, by issuing a command to the grinding head pressure control device. In another embodiment, the motion control unit is configured to issue a command to the grinding head lifting device to continuously raise the grinding head at a first speed until the entire workpiece leaves the grinding pad; and to raise the grinding head at a second speed higher than the first speed after the entire workpiece leaves the grinding pad. In one embodiment, a computer-readable recording medium is provided, the medium containing a program for causing a computer to perform the following steps: while issuing commands to a grinding head pressure control device, a grinding table rotation device, and a grinding head rotation device to rotate the grinding head and a grinding pad on the grinding table, a workpiece is pressed against the grinding pad to grind the workpiece; after grinding the workpiece, commands are issued to the grinding table rotation device and the grinding head rotation device to stop the rotation of the grinding pad and the grinding head; a command is issued to the grinding head pressure control device to raise the retaining ring relative to the workpiece, thereby separating the retaining ring from the grinding pad and moving the retaining ring to a position higher than the workpiece; and a command is issued to the grinding head lifting device to raise the grinding head while the workpiece is held on the grinding head. (Effects of the Invention) According to the present invention, the retaining ring is raised to a position higher than the workpiece before the grinding head is raised. Therefore, the workpiece does not contact the retaining ring when the grinding head rises, and the workpiece does not bend downwards due to the retaining ring. As a result, excessive stress is not generated on the workpiece, preventing workpiece breakage. Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG1 is a schematic diagram showing one embodiment of the polishing apparatus. The polishing apparatus is a device for chemically and mechanically polishing a workpiece W used in the manufacture of semiconductor devices such as wafers, substrates (e.g., circular substrates, corner substrates), and panels. In the embodiment shown in FIG1, a wafer is used as the workpiece W. As shown in Figure 1, the grinding apparatus includes: a grinding table 5 that supports a grinding pad 2 having a grinding surface 2a; a grinding head 7 that presses a workpiece W against the grinding surface 2a; and a grinding fluid supply nozzle 8 that supplies grinding fluid (e.g., a slurry containing abrasive particles) to the grinding surface 2a. The grinding head 7 is configured to hold the workpiece W on its lower surface. The grinding apparatus also includes a support shaft 14, a grinding head swing arm 16 connected to the upper end of the support shaft 14, a grinding head shaft 18 rotatably supported on the free end of the grinding head swing arm 16, and a grinding head rotating device 20 for rotating the grinding head shaft 18 and the grinding head 7. The grinding head 7 is fixed to the lower end of the grinding head shaft 18. The grinding head rotating device 20 is fixed to the grinding head swing arm 16. The grinding head rotating device 20 includes a motor, a torque transmission device, etc., but its structure is not particularly limited. The grinding head rotating device 20 is connected to the grinding head shaft 18 and configured to rotate the grinding head shaft 18 and the grinding head 7 in the direction indicated by the arrow. A rotary joint 22 is connected to the upper end of the grinding head shaft 18. The grinding apparatus also includes a grinding head lifting device 25 that moves the grinding head 7 and the grinding head shaft 18 up and down relative to the grinding table 5 and the grinding head swing arm 16. This grinding head lifting device 25 may have a combination of a ball screw mechanism and a servo motor, or an actuator such as a cylinder, but its structure is not particularly limited. When the grinding head lifting device 25 moves the grinding head shaft 18 up and down relative to the grinding head swing arm 16, the grinding head 7 moves up and down relative to the grinding head swing arm 16 and the grinding table 5, as indicated by the arrow. The grinding apparatus also includes a grinding table rotation device 30 that rotates the grinding pad 2 and the grinding table 5 about their respective axes. The grinding table rotation device 30 is positioned below the grinding table 5, which is connected via a table shaft 5a. The grinding table rotation device 30 includes an actuator such as a motor, but its structure is not particularly limited. The grinding table 5 and the grinding pad 2 rotate integrally about the table shaft 5a in the direction indicated by the arrow via the grinding table rotation device 30. The grinding pad 2 is attached to the upper surface of the grinding table 5. The exposed surface of the grinding pad 2 forms the grinding surface 2a for grinding workpieces such as wafers W. The grinding apparatus also includes a grinding head pressure control device 33 for controlling the pressure within the grinding head 7. This grinding head pressure control device 33 is configured to actuate components of the grinding head 7 (e.g., the retaining ring or elastic diaphragm described later). In this embodiment, the grinding head pressure control device 33 includes a pressure regulator (not shown) that adjusts the pressure of a gas (e.g., air) that serves as the working fluid for actuating the components of the grinding head 7. For example, by adjusting the pressure of the gas supplied to the grinding head 7 using the pressure regulator, the force with which the grinding head 7 presses the workpiece W against the grinding pad 2 can be adjusted. The grinding head pressure control device 33 is connected to a rotary joint 22, through which gas at a predetermined pressure is supplied to the grinding head 7. The grinding apparatus also includes a grinding head moving device 37 that moves the grinding head 7 in a direction parallel to the grinding surface 2a of the grinding pad 2. This grinding head moving device 37 is fixed to the upper end of the support shaft 14 and connected to the grinding head swing arm 16. By rotating the grinding head swing arm 16 around the support shaft 14, the grinding head 7 supported on the grinding head swing arm 16 can be moved in a direction parallel to the grinding surface 2a of the grinding pad 2. However, the structure of the grinding head moving device 37 is not limited to this embodiment. In one embodiment, the grinding head moving device 37 may also be configured to be connected to the lower part of the support shaft 14, so that the support shaft 14 and the grinding head swing arm 16 rotate integrally around the support shaft 14. The grinding apparatus also includes a motion control unit 40 that controls the overall movement of the grinding apparatus, including the grinding head rotation device 20, the grinding head lifting device 25, the grinding table rotation device 30, the grinding head pressure control device 33, and the grinding head moving device 37. The motion control unit 40 has at least one computer. The motion control unit 40 may also have multiple computers. For example, the motion control unit 40 may also be composed of a combination of an edge server and a cloud server. The motion control unit 40 includes a storage device 40a and a processing unit 40b. The processing unit 40b includes a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit) that performs calculations according to commands contained in a program stored in the storage device 40a. The storage device 40a includes a main storage device (e.g., random access memory) accessible by the processing unit 40b and an auxiliary storage device (e.g., a hard disk drive or a solid-state drive) for storing data and programs. However, the specific structure of the motion control unit 40 is not limited to these examples. The grinding of workpiece W is performed as follows. Workpiece W is held in the grinding head 7 with its grinding surface facing down. While the grinding head 7 and the grinding table 5 are rotated, grinding fluid (e.g., a slurry containing abrasive particles) is supplied to the grinding surface 2a of the grinding pad 2 from the grinding fluid supply nozzle 8 located above the grinding table 5. The grinding pad 2 rotates integrally with the grinding table 5 around its central axis. The grinding head 7 is lowered to a predetermined grinding height by the grinding head lifting device 25. Furthermore, while maintaining the above-mentioned grinding height, the grinding head 7 presses the workpiece W against the grinding surface 2a of the grinding pad 2. The workpiece W rotates integrally with the grinding head 7. With the grinding fluid present on the grinding surface 2a of the grinding pad 2, the workpiece W slides in contact with the grinding surface 2a. The surface of the workpiece W is ground by a combination of the chemical action of the grinding fluid and the abrasive particles contained in the grinding fluid and / or the mechanical action of the grinding pad 2. Next, the details of the grinding head 7 will be described. Figure 2 is a cross-sectional view showing one embodiment of the grinding head 7. The grinding head 7 includes a head body 45 and a retaining ring 48. The head body 45 includes a carrier 50 connected to the grinding head shaft 18 and a first elastic membrane 51 mounted on the lower surface of the carrier 50. The lower surface of the first elastic membrane 51 forms a pressing surface 51a for pressing the workpiece W against the polishing pad 2. This pressing surface 51a contacts the upper surface of the workpiece W (the surface opposite to the polished surface). A plurality of first pressure chambers C1, C2, and C3 are formed between the carrier 50 and the first elastic membrane 51. That is, a plurality of first pressure chambers C1, C2, and C3 are formed inside the first elastic membrane 51. The central first pressure chamber C1 is circular, the first pressure chamber C2 located outside the first pressure chamber C1 is annular, and the first pressure chamber C3 located outside the first pressure chamber C2 is annular. These first pressure chambers C1, C2, and C3 are arranged in a concentric circle. The first pressure chambers C1, C2, and C3 are connected to the grinding head pressure control device 33 via first fluid lines F1, F2, and F3 and a rotary joint 22. In this embodiment, the grinding head pressure control device 33 includes a pressure regulator (not shown) that supplies gas at a predetermined pressure to the grinding head 7. When fluid (e.g., air) is supplied to the first pressure chambers C1, C2, and C3, the pressing surface 51a of the first elastic membrane 51, subjected to the fluid pressure within the first pressure chambers C1, C2, and C3, presses the workpiece W against the grinding surface 2a of the grinding pad 2. The number of first pressure chambers C1, C2, and C3 is not limited to the embodiment shown in FIG2. In one embodiment, a single first pressure chamber may also be provided between the carrier 50 and the first elastic membrane 51. The retaining ring 48 is configured to surround the workpiece W and the first elastic membrane 51. More specifically, the retaining ring 48 is configured to surround the outer edge of the workpiece W and the pressing surface 51a of the first elastic membrane 51. The upper part of the retaining ring 48 is connected to an annular retaining ring pressing mechanism 60. The retaining ring pressing mechanism 60 is configured to apply a uniform downward load to the entire upper surface of the retaining ring 48, pressing the lower surface of the retaining ring 48 against the grinding surface 2a of the grinding pad 2. The retaining ring pressing mechanism 60 includes an annular second elastic diaphragm 62 mounted on the carrier 50. A second pressure chamber 65 is formed inside the second elastic diaphragm 62. This second pressure chamber 65 is connected to the grinding head pressure control device 33 via a second fluid line F4 and a rotary joint 22. When fluid (e.g., air or other gas) is supplied to the second pressure chamber 65 through the second fluid line F4, the second elastic diaphragm 62, under the pressure of the fluid within the second pressure chamber 65, presses the retaining ring 48 downwards as a whole. In this way, the retaining ring pressing mechanism 60 presses the lower surface of the retaining ring 48 against the grinding surface 2a of the grinding pad 2. When a negative pressure is created in any of the first pressure chambers C1, C2, and C3 by the grinding head pressure control device 33, the workpiece W is held by vacuum suction on the pressing surface 51a of the first elastic membrane 51. For example, as shown in FIG3, when a negative pressure is created in the first pressure chambers C2 and C3, the pressing surface 51a of the first elastic membrane 51 is concave upward, and the first elastic membrane 51 functions as a suction cup to attract the workpiece W. When attracting the workpiece W to the first elastic membrane 51, a negative pressure can be created in only one of the first pressure chambers C1, C2, and C3, or a negative pressure can be created in all of the first pressure chambers C1, C2, and C3. In one embodiment, the pressing surface 51a of the first elastic membrane 51 may also have a through hole (not shown) communicating with at least one of the first pressure chambers C1, C2, and C3. In this case, when a negative pressure is formed in the first pressure chamber communicating with the through hole, a negative pressure is also formed in the through hole, and the workpiece W can be attracted to the pressing surface 51a of the first elastic membrane 51 by means of this negative pressure. As shown in Figure 4, when a negative pressure is created in the second pressure chamber 65 by the grinding head pressure control device 33, the retaining ring 48 rises relative to the first elastic membrane 51, the carrier 50, and the workpiece W, moving away from the grinding pad 2. On the other hand, when pressurized fluid is supplied to the second pressure chamber 65 by the grinding head pressure control device 33, as shown in Figure 2, the retaining ring 48 descends relative to the first elastic membrane 51, the carrier 50, and the workpiece W, pressing against the grinding pad 2. In this way, the grinding head pressure control device 33 can move the retaining ring 48 up and down by changing the pressure in the second pressure chamber 65. Figure 5 illustrates the release of the ground workpiece W from the grinding head 7. After grinding the workpiece W, the grinding head 7 moves together with the workpiece W to the workpiece contact position. At this workpiece contact position, fluid (e.g., air or other gas) is supplied into the first pressure chambers C1, C2, and C3, causing the first elastic membrane 51 to expand. Then, a jet of release fluid (e.g., pure water, gas, or a mixture thereof) is released from the release nozzle 71 to the contact portion between the workpiece W and the first elastic membrane 51, thereby releasing the workpiece W from the grinding head 7. During the release of the workpiece W, as shown in Figure 5, the retaining ring 48 is positioned higher than the workpiece W. Therefore, the release fluid can reach the contact portion between the workpiece W and the first elastic membrane 51. The released workpiece W is received by a conveying device (not shown) and transported for the next process. Next, the operation of the grinding head 7 during and after grinding the workpiece W will be described with reference to FIG6. FIG6 is a flowchart illustrating one embodiment of the operation of the grinding head 7 during and after grinding the workpiece W. In step 1, the motion control unit 40 issues commands to the grinding table rotation device 30 and the grinding head rotation device 20, causing the grinding pad 2 and the grinding head 7 to rotate at predetermined speeds. Grinding fluid is supplied to the rotating grinding pad 2 from the grinding fluid supply nozzle 8. The motion control unit 40 issues commands to the grinding head lifting device 25, causing the grinding head 7 to descend to a predetermined grinding action height. The motion control unit 40 further issues commands to the grinding head pressure control device 33, supplying pressurized fluid to the first pressure chambers C1, C2, C3 and the second pressure chamber 65 of the grinding head 7, pressing the workpiece W and the retaining ring 48 against the grinding surface 2a of the grinding pad 2 (see Figure 2). The workpiece W slides in contact with the grinding surface 2a of the grinding pad 2 while the grinding fluid is present on the grinding pad 2. The surface of workpiece W is ground by a combination of the chemical action of the grinding fluid and the mechanical action of the abrasive particles contained in the grinding fluid and / or the grinding pad 2. During the grinding of workpiece W, the grinding pad 2 rotates integrally with the grinding table 5, and the workpiece W rotates integrally with the grinding head 7. During the grinding of workpiece W, the grinding head 7 is maintained at the aforementioned grinding action height. The grinding action height is the overall relative height of the grinding head 7 with respect to the grinding surface 2a of the grinding pad 2. In step 2, after the grinding of workpiece W is completed, the pressure of workpiece W against grinding pad 2 based on grinding head 7 is stopped. After the grinding of workpiece W is completed, the supply of grinding fluid to grinding pad 2 also stops. In step 3, the motion control unit 40 issues commands to the grinding table rotation device 30 and the grinding head rotation device 20 to stop the rotation of the grinding pad 2 and the grinding head 7. The grinding table rotation device 30 stops the rotation of the grinding table 5, thereby stopping the rotation of the grinding pad 2 as well. In step 4, the motion control unit 40 issues a command to the grinding head pressure control device 33, causing the retaining ring 48 to rise relative to the workpiece W, thereby separating the retaining ring 48 from the grinding pad 2 and moving the retaining ring 48 to a position higher than the workpiece W (see Figure 4). During the relative rise of the retaining ring 48 relative to the workpiece W, the rotation of the grinding pad 2 and the grinding head 7 has stopped. Therefore, the workpiece W will not fly off the grinding head 7, and the relative position of the workpiece W relative to the grinding head 7 will not change. During the relative rise of the retaining ring 48 relative to the workpiece W, the grinding head 7 remains at the aforementioned grinding action height, and the workpiece W is in contact with the grinding pad 2. In step 5, the motion control unit 40 issues a command to the grinding head pressure control device 33 to keep the workpiece W in place by the grinding head 7. More specifically, a negative pressure is formed in at least one of the first pressure chambers C1 to C3 of the grinding head 7, and the workpiece W is attracted to the pressing surface 51a of the first elastic membrane 51 by vacuum suction. At this time, at least a portion of the workpiece W is slightly pulled up from the grinding pad 2. In step 6, the motion control unit 40 issues a command to the grinding head lifting device 25, causing the grinding head 7, which holds the workpiece W, to rise as a whole. The grinding head 7 and the workpiece W rise together to a position higher than the height of the aforementioned grinding action. When the grinding head 7 and the workpiece W are raised, the rotation of the grinding pad 2 and the grinding head 7 has stopped. In step 7, the motion control unit 40 issues a command to the grinding head moving device 37, causing the grinding head swing arm 16 to rotate around the support shaft 14, so that the grinding head 7 and the workpiece W are moved to the specified workpiece handover position. In step 8, at the workpiece junction, a jet of release fluid (e.g., pure water, gas, or a mixture thereof) is released from the release nozzle 71 to the contact portion between the workpiece W and the first elastic membrane 51 (see Figure 5), thereby releasing the workpiece W from the grinding head 7. According to the embodiment shown in Figure 6, before the grinding head 7 is raised from the grinding pad 2, the retaining ring 48 is raised to a position higher than the workpiece W (see Figure 4). Therefore, when the grinding head 7 rises, the workpiece W will not contact the retaining ring 48, and the workpiece W will not bend downwards due to the retaining ring 48. As a result, excessive stress will not be generated on the workpiece W, and breakage of the workpiece W can be prevented. In the embodiment shown in FIG6, the retaining ring 48 is raised in step 4, and then the workpiece W is held in the grinding head 7 in step 5. However, in one embodiment, the raising of the retaining ring 48 in step 4 and the holding of the workpiece W by the grinding head 7 in step 5 can be performed simultaneously. Moreover, in other embodiments, the workpiece W can be held in the grinding head 7 in step 4, and then the retaining ring 48 is raised in step 5. However, as explained with reference to FIG17, when wear grooves are formed on the inner surface of the retaining ring 48 due to contact with the workpiece W, the order of steps 4 and 5 shown in FIG6 is preferred. This is because when the workpiece W is held in the grinding head 7, the first pressure chamber C3 shrinks due to negative pressure, the workpiece W is slightly lifted, the outer edge of the workpiece W hooks into the wear groove, and the workpiece W may bend. Figure 7 is a flowchart illustrating another embodiment of the operation of the grinding head 7 during and after grinding of the workpiece W. The specific actions of each step, unless otherwise specified, are the same as those described with reference to Figure 6, therefore repeated descriptions are omitted. As shown in Figure 7, in this embodiment, in step 3, the ground workpiece W is held on the grinding head 7, and then in step 4, the rotation of the grinding pad 2 and the grinding table 5 is stopped. Furthermore, in step 5, the holding ring 48 is raised to a position higher than the workpiece W. Between steps 3 and 4, the holding ring 48 remains in contact with the grinding pad 2. The embodiment shown in Figure 7 has the following advantages: when the workpiece W is held on the grinding head 7, the grinding pad 2 and the grinding table 5 rotate, thus reducing the tightness due to the entry of liquid or air between the workpiece W and the grinding pad 2, and enabling a reliable suction action of the workpiece W towards the pressing surface 51a based on the grinding head 7. On the other hand, when wear grooves caused by contact with the workpiece W are formed on the inner surface of the retaining ring 48, the embodiment shown in Figure 6 is preferred for the above reasons. Figures 8 and 9 are schematic diagrams illustrating an example of the action of the grinding head 7 holding the workpiece W. In Figures 8 and 9, the grinding head 7 is simplified, and the deformation of the workpiece W is exaggerated. In the example shown in Figure 8, negative pressure is formed sequentially from the outermost pressure chamber among the plurality of first pressure chambers C1 to C3. That is, negative pressure is initially formed in the outermost first pressure chamber C3, and then negative pressure is formed in the innermost first pressure chamber C2. By forming negative pressure in the first pressure chambers C3 and C2 in this order, the outer portion of the workpiece W is slightly lifted by the first elastic membrane 51, forming an open gap between the outer portion of the workpiece W and the grinding pad 2. In contrast, in the example shown in Figure 9, negative pressure is formed sequentially from the innermost pressure chamber among the plurality of first pressure chambers C1 to C3. That is, negative pressure is initially formed in the innermost first pressure chamber C1, and then in the outermost first pressure chamber C2. When negative pressure is formed in the first pressure chambers C1 and C2 in this order, the central part of the workpiece W is slightly lifted by the first elastic membrane 51, forming a closed space S between the central part of the workpiece W and the grinding pad 2. Because negative pressure is formed in this closed space S, the entire workpiece W functions as a suction cup, preventing the workpiece W from being held on the grinding head 7. Therefore, it is preferable to initially create a negative pressure in the outer first pressure chamber C3, and then create a negative pressure in the inner first pressure chamber C2. Through this workpiece W holding action, the grinding head 7 can smoothly hold the workpiece W. In one embodiment, as shown in FIG10, fluid may also be supplied between the workpiece W and the grinding pad 2 while the grinding head 7 holds the workpiece W. More specifically, the grinding apparatus includes a fluid supply system 80 for supplying fluid between the workpiece W and the grinding pad 2. The fluid supply system 80 includes a fluid line 81 for supplying fluid (e.g., liquid, gas, or a mixture thereof) to the grinding surface 2a of the grinding pad 2 and an actuator-driven valve 82 connected to the fluid line 81. Fluid line 81 extends within the grinding table 5, and fluid flows out through opening 83 formed in the grinding pad 2 onto the grinding surface 2a of the grinding pad 2. Examples of actuator-driven valve 82 include electric valves, solenoid valves, and pneumatic valves. The actuator-driven valve 82 is electrically connected to the motion control unit 40, and the operation of the actuator-driven valve 82 is controlled by the motion control unit 40. The motion control unit 40 issues a command to the grinding head pressure control device 33 to keep the workpiece W in place by the grinding head 7. Simultaneously, the motion control unit 40 issues a command to the fluid supply system 80 to supply fluid between the workpiece W and the grinding pad 2. Through this action, while fluid flows in the gap between the workpiece W and the grinding pad 2, the workpiece W is held in place by the grinding head 7. The flow of fluid in the gap between the workpiece W and the grinding pad 2 reduces the surface tension of the liquid acting between them. As a result, the grinding head 7 can reliably hold the workpiece W. In one embodiment, during the process of lifting the grinding head 7 and the workpiece W together from the grinding pad 2, the motion control unit 40 may also issue a command to the fluid supply system 80 to supply fluid between the workpiece W and the grinding pad 2. The flow of fluid in the gap between the workpiece W and the grinding pad 2 reduces the surface tension of the liquid acting between the workpiece W and the grinding pad 2. As a result, the grinding head 7 is able to smoothly separate the workpiece W from the grinding pad 2 as it rises. In step 6, as described with reference to Figures 6 and 7, the grinding head 7 rises together with the workpiece W while the holding ring 48 is positioned higher than the workpiece W. At this time, the workpiece W remains on the grinding head 7, but a portion of the workpiece W sometimes contacts the grinding pad 2. When the grinding head 7 rises together with the workpiece W while a portion of the workpiece W is in contact with the grinding pad 2, the workpiece W deforms due to the surface tension of the liquid present between the workpiece W and the grinding pad 2, potentially generating excessive stress on the workpiece W. Therefore, in the embodiments described below, the grinding head 7 is raised at a first speed until the entire workpiece W moves away from the grinding pad 2; and after the entire workpiece W moves away from the grinding pad 2, the grinding head 7 is raised at a second speed higher than the first speed. Figures 11(a) and 11(b) are schematic diagrams illustrating an embodiment in which the rising speed of the grinding head 7 is switched from a first speed to a second speed. In Figures 11(a) and 11(b), the grinding head 7 is depicted in a simplified manner. The grinding apparatus includes a workpiece detector 90 configured to detect the moment when the workpiece W leaves the grinding pad 2. The workpiece detector 90 is disposed within the grinding table 5. The structure of the workpiece detector 90 is not particularly limited as long as it can detect the moment when the workpiece W leaves the polishing pad 2. The workpiece detector 90 can also be a known sensor. For example, the workpiece detector 90 can be a displacement sensor that detects the displacement of the workpiece W or a film thickness sensor (e.g., an eddy current sensor or an optical film thickness sensor) that detects the thickness of the film on the workpiece W. In other examples, the workpiece detector 90 can also be configured to detect the moment when the workpiece W leaves the polishing pad 2 based on changes in pressure or flow rate of the fluid flowing between the polishing pad 2 and the workpiece W from the opening of the polishing pad 2. As shown in Figure 11(a), the motion control unit 40 issues a command to the grinding head lifting device 25 (refer to Figure 1) to cause the grinding head 7 to rise at a first speed until the entire workpiece W leaves the grinding pad 2. When the motion control unit 40 receives a signal from the workpiece detector 90 indicating that the entire workpiece W has left the grinding pad 2, as shown in Figure 11(b), the motion control unit 40 issues a command to the grinding head lifting device 25 (refer to Figure 1) to cause the grinding head 7 to rise at a second speed higher than the first speed. By performing this action, the stress on the workpiece W can be continuously reduced until it leaves the grinding pad 2, and the grinding head 7 can be quickly raised after the workpiece W leaves the grinding pad 2, thereby increasing throughput. Figures 12(a) and 12(b) are top views illustrating the operation of the grinding head 7 after the workpiece W has been ground. Unless otherwise specified, the specific operations of this embodiment are the same as those of the embodiment described with reference to Figures 6 and 7, therefore, repeated descriptions are omitted. In this embodiment, after grinding the workpiece W, the grinding head 7 moves from the grinding position shown in FIG12(a) for grinding the workpiece W to the overhang position shown in FIG12(b) for raising the workpiece W. More specifically, after grinding the workpiece W, while the grinding pad 2 and the grinding head 7 are rotating, the motion control unit 40 issues a command to the grinding head moving device 37, causing the grinding head 7 to move from the grinding position shown in FIG12(a) to the overhang position shown in FIG12(b). The overhang position is where a portion of the workpiece W held by the grinding head 7 extends outward in the radial direction from the grinding pad 2. The action of moving the grinding head 7 to the extended position is performed after the workpiece W has been ground and before the workpiece W is held in the grinding head 7. For example, in the flowchart shown in FIG6, the action of moving the grinding head 7 to the extended position is performed after stopping the pressing of the workpiece W against the grinding pad 2 in step 2, and before stopping the rotation of the grinding pad 2 and the grinding table 5 in step 3. In the flowchart shown in FIG7, the action of moving the grinding head 7 to the extended position is performed after stopping the pressing of the workpiece W against the grinding pad 2 in step 2, and before holding the workpiece W in step 3 by the grinding head 7. In the extended position, a portion of the workpiece W lies outside the grinding head 7, thus reducing the surface tension of the liquid acting between the workpiece W and the grinding pad 2. Therefore, the grinding head 7 can reliably hold the workpiece W. After the grinding head 7 and the workpiece W rise together from the grinding pad 2, the motion control unit 40 issues a command to the grinding head moving device 37, causing the grinding head 7 and the workpiece W to move to the workpiece contact position TP shown in FIG12(b). At the workpiece contact position TP, as explained with reference to FIG5, a jet of release fluid (e.g., pure water, gas, or a mixture thereof) is released from the release nozzle 71 to the contact portion between the workpiece W and the grinding head 7, thereby releasing the workpiece W from the grinding head 7. The embodiments described above are intended to enable those skilled in the art to carry out the present invention. Various modifications of the above embodiments will be apparent to those skilled in the art, and the technical concept of the present invention can be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is interpreted as encompassing the widest scope of the technical concept as defined by the claims. 2: Grinding pad 2a: Grinding surface 5: Grinding table 7: Grinding head 8: Grinding fluid supply nozzle 14: Support shaft 16: Grinding head swing arm 18: Grinding head shaft 20: Grinding head rotating device 22: Rotary joint 25: Grinding head lifting device 30: Grinding table rotating device 33: Grinding head pressure control device 37: Grinding head moving device 40: Motion control unit 40a: Storage device 40b: Calculation device 45: Head body 48: Holding ring 50: Carrier 51: First elastic membrane 51a: Pressing surface 60: Holding ring pressing mechanism 62: Second elastic membrane 65: Second pressure chamber 80: Fluid supply system 81: Fluid line 82: Actuator driven valve 90: Workpiece detector W: Workpiece C1: First pressure chamber C2: First pressure chamber C3: First pressure chamber F1: First fluid line F2: First fluid line F3: First fluid line F4: Second fluid line Figure 1 is a schematic diagram showing one embodiment of the grinding apparatus. Figure 2 is a cross-sectional view showing one embodiment of the grinding head. Figure 3 is a diagram illustrating the case where the first elastic membrane of the grinding head holds the workpiece by vacuum attraction. Figure 4 is a diagram illustrating the case where the holding ring rises relative to the workpiece and separates from the grinding pad. Figure 5 is a diagram illustrating the case where the ground workpiece is released from the grinding head. Figure 6 is a flowchart illustrating one embodiment of the operation of the grinding head during and after grinding the workpiece. Figure 7 is a flowchart illustrating another embodiment of the operation of the grinding head during and after grinding the workpiece. Figure 8 is a schematic diagram showing an example of the operation of the grinding head holding the workpiece. Figure 9 is a schematic diagram showing an example of the operation of the grinding head holding the workpiece. Figure 10 is a diagram illustrating an embodiment of supplying fluid between the workpiece and the grinding pad when the grinding head holds the workpiece. Figures 11(a) and 11(b) are schematic diagrams illustrating an embodiment of switching the rising speed of the grinding head from a first speed to a second speed. Figures 12(a) and 12(b) are top views illustrating yet another embodiment of the operation of the grinding head after grinding the workpiece. Figure 13 is a schematic diagram showing a conventional grinding apparatus. Figure 14 is a cross-sectional view showing a portion of the grinding head shown in Figure 13. Figure 15 is a diagram illustrating the conventional case where the grinding head holds the workpiece. Figure 16 is a diagram illustrating the case where the workpiece bends downwards as the grinding head rises. Figure 17 is a diagram illustrating the case where the workpiece bends downwards as the grinding head rises. 2: Grinding pad 2a: Grinding surface 5: Grinding table 7: Grinding head 18: Grinding head shaft 22: Rotary joint 33: Grinding head pressure control device 45: Head Body 48: Keeping ring 50: Carrier 51: First elastic membrane 51a: Pressing surface 60: Retaining ring pressing mechanism 62: Second elastic membrane 65: Second pressure chamber W: Workpiece C1: First pressure chamber C2: First pressure chamber C3: First pressure chamber F1: First fluid circuit F2: First fluid circuit F3: First fluid circuit F4: Second fluid circuit

Claims

1. A method for raising the grinding head after workpiece grinding, wherein, While rotating the grinding head and grinding pad, the workpiece is pressed against the grinding pad to grind it. With the workpiece and the retaining ring of the grinding head in contact with the grinding pad, the rotation of the grinding pad and grinding head is stopped, the retaining ring is separated from the grinding pad, and the retaining ring is moved to a position higher than the workpiece. Then, the workpiece is held on the grinding head by vacuum suction. After that, with the workpiece held on the grinding head by vacuum suction, the workpiece is separated from the grinding pad by raising the grinding head.

2. The method according to request item 1, wherein, The method further includes the following step: holding the workpiece in the grinding head by vacuum suction before separating the retaining ring from the grinding pad.

3. The method according to request item 1 or 2, wherein, The process of holding the workpiece using the grinding head is carried out while fluid is directly supplied between the workpiece and the grinding pad.

4. The method according to request item 1 or 2, wherein, The grinding head has an elastic membrane forming a plurality of pressure chambers for pressing the workpiece against the grinding pad. The process of holding the workpiece using the grinding head involves creating a negative pressure in the outer pressure chamber of the plurality of pressure chambers and then creating a negative pressure in the inner pressure chamber, thereby holding the workpiece using the grinding head.

5. The method according to request item 1 or 2, wherein, The process of raising the grinding head includes the following steps: raising the grinding head at a first speed until the entire workpiece leaves the grinding pad; and raising the grinding head at a second speed higher than the first speed after the entire workpiece leaves the grinding pad.

6. A grinding apparatus for a workpiece, wherein, Includes: a grinding table for supporting the grinding pad; A grinding table rotation device that causes the grinding table and the grinding pad to rotate together; A grinding head that presses the workpiece against the grinding pad to grind the workpiece; A grinding head pressure control device that controls the pressure inside the grinding head; A grinding head rotating device that rotates the grinding head; A grinding head lifting device that allows the grinding head to move up and down relative to the grinding table; The system includes an action control unit that controls the operation of the grinding table rotation device, the grinding head pressure control device, the grinding head rotation device, and the grinding head lifting device. The grinding head has a retaining ring surrounding the workpiece. The action control unit is configured to, after grinding the workpiece, issue commands to the grinding table rotation device and the grinding head rotation device to stop the rotation of the grinding pad and the grinding head while the workpiece and the retaining ring are in contact with the grinding pad. It then issues commands to the grinding head pressure control device to separate the retaining ring from the grinding pad and move the retaining ring to a position higher than the workpiece. After that, it holds the workpiece on the grinding head by vacuum suction. Finally, it issues commands to the grinding head lifting device to separate the workpiece from the grinding pad by raising the grinding head while the workpiece is held on the grinding head by vacuum suction.

7. The grinding apparatus according to claim 6, wherein, The motion control unit is configured to issue a command to the grinding head lifting device to hold the workpiece on the grinding head by vacuum suction before the retaining ring is separated from the grinding pad.

8. The grinding apparatus according to claim 6 or 7, wherein, The grinding apparatus further includes a fluid supply system for supplying fluid between the workpiece and the grinding pad. The motion control unit is configured to issue a command to the fluid supply system to directly supply fluid between the workpiece and the grinding pad while keeping the grinding head holding the workpiece.

9. The grinding apparatus according to claim 6 or 7, wherein, The grinding head has an elastic membrane forming a plurality of pressure chambers for pressing the workpiece against the grinding pad. The motion control unit is configured to issue a command to the grinding head pressure control device to create a negative pressure in the outer pressure chamber of the plurality of pressure chambers and then create a negative pressure in the inner pressure chamber, thereby using the grinding head to hold the workpiece.

10. The grinding apparatus according to claim 6 or 7, wherein, The motion control unit is configured to issue a command to the grinding head lifting device to continuously raise the grinding head at a first speed before the entire workpiece leaves the grinding pad; and to raise the grinding head at a second speed higher than the first speed after the entire workpiece leaves the grinding pad.

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