METHOD OF INFLATING ELASTIC MEMBRANE OF POLISHING HEAD, AND POLISHING HEAD SYSTEM

CROSS REFERENCE TO RELATED APPLICATION

This document claims priority to Japanese Patent Application No. 2023-028037 filed Feb. 27, 2023, the entire contents of which are hereby incorporated by reference.

BACKGROUND

Chemical mechanical polishing (CMP) is a technique of polishing a surface of a wafer by pressing the wafer against a polishing surface while supplying a polishing liquid onto the polishing surface to place the wafer in sliding contact with the polishing surface in the presence of the polishing liquid. During polishing of the wafer, the wafer is pressed against the polishing surface by a polishing head. The surface of the wafer is planarized by a chemical action of the polishing liquid and mechanical action(s) of abrasive grains contained in the polishing liquid and/or a polishing pad.

FIG. 7 is a cross-sectional view schematically showing an example of a polishing head 100. The polishing head 100 has an elastic membrane 110 to be contact an upper surface of a wafer W1. This elastic membrane 110 has a shape that forms a plurality of pressure chambers 101 to 104. A pressure in each of the pressure chambers 101 to 104 can be regulated independently. Therefore, the polishing head 100 can press a plurality of regions of the wafer W1 corresponding to these pressure chambers 101 to 104 with different forces, and can achieve a desired film-thickness profile of the wafer W1.

When the polishing of the wafer W1 is terminated, the polished wafer W1 is moved to a position above a wafer transfer device 114 by the polishing head 100, as shown in FIG. 8. Then, pressures in the pressure chambers 101 to 104 are increased until the elastic membrane 110 is curved downward, so that a gap is formed between an edge portion of the wafer W1 and the elastic membrane 110. Release nozzles 115 emit a release gas (for example, an inert gas, such as nitrogen gas) into the gap between the edge portion of the wafer W1 and the elastic membrane 110. As a result, the wafer W1 is released from the polishing head 100 and received by the wafer transfer device 114, as shown in FIG. 9. Thereafter, the polished wafer W1 is transported to the next process, such as a cleaning process.

FIG. 10 is a schematic diagram showing a state in which a wafer W2 to be polished next is placed on the wafer transfer device 114. As shown in FIG. 10, the next wafer W2 is transported onto the wafer transfer device 114 below the polishing head 100 by a transport device (not shown), such as a transfer robot. At the same time, the polishing head 100 is cleaned with a liquid (for example, pure water) supplied from cleaning nozzles 120, so that polishing liquid and polishing debris are removed from the polishing head 100.

The liquid used to clean the polishing head 100 falls onto an upper surface of the wafer W2. If the liquid exists between the wafer W2 and the elastic membrane 110 of the polishing head 100 when the wafer W2 is being polished, the polishing head 100 cannot appropriately apply force to the wafer W2. In order to prevent this, as shown in FIG. 11, before the polishing head 100 holds the wafer W2, the pressures in the pressure chambers 101 to 104 are increased to curve the elastic membrane 110 downward. Then, as shown in FIG. 12, the polishing head 100 is lowered until the downwardly curved elastic membrane 110 pushes the liquid outside the wafer W2, so that the liquid is removed from the upper surface of the wafer W2.

As wafers tend to become smaller and more multilayered, wafers are becoming brittle and are more easily broken. As shown in FIGS. 8 and 12, when the downwardly curved elastic membrane 110 contacts the wafer, a stress is generated in the wafer. In the conventional technology, the pressures in the pressure chambers 101 to 104 are controlled when the elastic membrane 110 is inflated. However, the pressure chambers 101 to 104 may not be inflated into a desired shape due to various causes, such as individual difference in the elastic membrane 110, a structure or material of the elastic membrane 110 itself, aging deterioration of the elastic membrane 110, etc. For example, the elastic membrane 110 may be inflated excessively or may be inflated locally. Due to individual difference in the elastic membrane 110, the pressures required to inflate the elastic membrane 110 may vary. Moreover, an amount of inflation of the elastic membrane 110 also varies depending on volumes of the pressure chambers 101 to 104, pressure loss in pipes, etc. Therefore, predictive control using pressure is difficult. As a result, excessive stress may be generated in the wafer and the wafer may be damaged. Such problems are expected to become more prominent as the number of pressure chambers of the polishing head increases. Specifically, as the number of pressure chambers of the polishing head increases, a volume per pressure chamber decreases, and it is expected that the way of the inflation of the pressure chambers will be more susceptible to pressure and flow rate.

SUMMARY

Therefore, a technique is provided that can allow an elastic membrane to be inflated into a desired shape when a workpiece (e.g., a wafer, substrate, or panel) is released from a polishing head, or when the workpiece is held on the polishing head, thereby avoiding excessive stress on the workpiece.

Embodiments described below relate to a technique for inflating an elastic membrane of a polishing head to force a workpiece (e.g., a wafer, substrate, or panel) against a polishing pad, and in particular relate to a technique for inflating the elastic membrane when the workpiece is released from the polishing head or when the workpiece is held on the polishing head.

In an embodiment, there is disclosed a method of inflating an elastic membrane of a polishing head, comprising: supplying a gas into a first pressure chamber and a second pressure chamber at a first flow rate and a second flow rate regulated by a first flow-rate control valve and a second flow-rate control valve when a polished workpiece is released from the polishing head, or when a workpiece to be polished is held on the polishing head, the first pressure chamber and the second pressure chamber being formed by the elastic membrane.

In an embodiment, a volume of the first pressure chamber is larger than a volume of the second pressure chamber, and the first flow rate is higher than the second flow rate.

In an embodiment, the gas is supplied into the first pressure chamber at the first flow rate until a cumulative value of the first flow rate reaches a first target flow-rate cumulative value, and the gas is supplied into the second pressure chamber at the second flow rate until a cumulative value of the second flow rate reaches a second target flow-rate cumulative value.

In an embodiment, the method further comprises: calculating the first flow rate by dividing a first target flow-rate cumulative value for the first pressure chamber by preset operating time; and calculating the second flow rate by dividing a second target flow-rate cumulative value for the second pressure chamber by preset operating time.

In an embodiment, the method further comprises changing at least one of the first flow rate and the second flow rate while supplying the gas into the first pressure chamber and the second pressure chamber.

In an embodiment, the method further comprises: measuring a flow rate of the gas supplied to the first pressure chamber while polishing a workpiece with the polishing head, the flow rate being measure by the first flow-rate control valve; calculating a polishing flow-rate cumulative value which is a cumulative value of the measured flow rate; and determining a malfunction of the elastic membrane or a polishing abnormality of the workpiece based on a change in the polishing flow-rate cumulative value.

In an embodiment, there is provided a polishing-head system for polishing a workpiece, comprising: a polishing head having an elastic membrane forming a first pressure chamber and a second pressure chamber; a first gas delivery line and a second gas delivery line that communicate with the first pressure chamber and the second pressure chamber, respectively; a first flow-rate control valve and a second flow-rate control valve coupled to the first gas delivery line and the second gas delivery line, respectively; and a system controller configured to instruct the first flow-rate control valve and the second flow-rate control valve to supply a gas into the first pressure chamber and the second pressure chamber at a first flow rate and a second flow rate when a polished workpiece is released from the polishing head, or when a workpiece to be polished is held on the polishing head.

In an embodiment, a volume of the first pressure chamber is larger than a volume of the second pressure chamber, and the first flow rate is higher than the second flow rate.

In an embodiment, the system controller is configured to: calculate a cumulative value of the first flow rate; instruct the first flow-rate control valve to supply the gas into the first pressure chamber at the first flow rate until the cumulative value of the first flow rate reaches a first target flow-rate cumulative value; calculate a cumulative value of the second flow rate; and instruct the second flow-rate control valve to supply the gas into the second pressure chamber at the second flow rate until the cumulative value of the second flow rate reaches a second target flow-rate cumulative value.

In an embodiment, the system controller is configured to: calculate the first flow rate by dividing a first target flow-rate cumulative value for the first pressure chamber by preset operating time; and calculate the second flow rate by dividing a second target flow-rate cumulative value for the second pressure chamber by preset operating time.

In an embodiment, the system controller is configured to instruct at least one of the first flow-rate control valve and the second flow-rate control valve to change at least one of the first flow rate and the second flow rate while the gas is supplied into the first pressure chamber and the second pressure chamber.

In an embodiment, the first flow-rate control valve is configured to measure a flow rate of the gas supplied to the first pressure chamber while a workpiece is polished with the polishing head; and the system controller is configured to calculate a polishing flow-rate cumulative value which is a cumulative value of the measured flow rate and determine a malfunction of the elastic membrane or a polishing abnormality of the workpiece based on a change in the polishing flow-rate cumulative value.

The inflation of the plurality of pressure chambers of the polishing head is controlled by the gas flow rate rather than gas pressure. An inflation speed of each pressure chamber and a volume of inflated pressure chamber can be easily and appropriately regulated by the corresponding flow-rate control valve. As a result, the elastic membrane can be reliably inflated into a desired shape, and excessive stress on workpiece (e.g., wafer) can be prevented. The gas with predetermined flow rates can be supplied into the pressure chambers, so that the amount of inflation of the elastic membranes can be controlled to be constant, and excessive stress can be prevented. If the flow rate of the gas to be fed can be clearly determined, a flow velocity can also be controlled based on a relationship between pressure and flow rate, so that the elastic membrane can be quickly and stably formed into a desired shape. Furthermore, since the workpiece can be quickly and reliably released from the polishing head, the amount of release gas (see FIGS. 8 and 9) to be supplied can be reduced. As a result, drying of the polished workpiece due to the release gas can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an embodiment of a polishing apparatus;

FIG. 2 is a cross-sectional view showing an embodiment of a polishing-head system;

FIG. 3 is a diagram illustrating an example of supplying compressed air to a plurality of pressure chambers at different flow rates when a polished wafer is released from a polishing head;

FIG. 4 is a diagram illustrating an example of supplying compressed air to the plurality of pressure chambers at different flow rates before a wafer to be polished is held on the polishing head;

FIG. 5 is a diagram illustrating an example of removing liquid from an upper surface of a wafer to be polished using a downwardly curved elastic membrane;

FIG. 6 is a graph showing an example of a temporal change in the flow rate of compressed gas supplied to the pressure chamber during polishing of a wafer;

FIG. 7 is a cross-sectional view schematically showing an example of the polishing head;

FIG. 8 is a diagram illustrating an example of curving the elastic membrane downward by changing the pressure within the plurality of pressure chambers;

FIG. 9 is a diagram showing a wafer when released from the elastic membrane of the polishing head;

FIG. 10 is a schematic diagram showing a state in which a wafer to be polished is placed on a wafer transfer device;

FIG. 11 is a diagram illustrating an example of curving the elastic membrane downward by changing the pressure in the plurality of pressure chambers; and

FIG. 12 is a diagram illustrating the curved elastic membrane when pressed against a wafer to push out liquid from the wafer.

DESCRIPTION OF EMBODIMENTS

Embodiments will now be described with reference to the drawings.

FIG. 1 is a schematic diagram showing an embodiment of a polishing apparatus. As shown in FIG. 1, the polishing apparatus includes a polishing table 3 configured to support a polishing pad 2, a polishing-head system 4 having a polishing head 1 configured to press a wafer W, which is an example of a workpiece, against the polishing pad 2, a table motor 6 configured to rotate the polishing table 3, and a polishing-liquid supply nozzle 5 configured to supply a polishing liquid (e.g., slurry containing abrasive grains) onto the polishing pad 2. The polishing pad 2 has a surface constituting a polishing surface 2a for polishing the wafer W.

The polishing table 3 is coupled to the table motor 6, which is configured to rotate the polishing table 3 and the polishing pad 2 together. The polishing head 1 is fixed to an end of a polishing-head shaft 11, and the polishing-head shaft 11 is rotatably supported by a head arm 15. The head arm 15 is rotatably supported by a support shaft 16. The polishing-head shaft 11 is coupled to a vertically moving mechanism 18 disposed in the head arm 15. The vertically moving mechanism 18 is configured to vertically move the polishing-head shaft 11 in its axial direction. The vertical movement of the polishing-head shaft 11 caused by the vertically moving mechanism 18 allows the wafer W held by the polishing head 1 to move close to and away from the polishing pad 2 on the polishing table 3.

The polishing apparatus further includes an operation controller 9 configured to control operations of each component of the polishing apparatus. The operation controller 9 is electrically coupled to the polishing head 1, the table motor 6, the polishing-liquid supply nozzle 5, and the vertically moving mechanism 18, and controls operations of the polishing head 1, the table motor 6, the polishing-liquid supply nozzle 5, and the vertical moving mechanism 18.

The operation controller 9 includes a memory 9a storing programs, and an arithmetic device 9b configured to perform arithmetic operations according to instructions contained in the programs. The operation controller 9 is composed of at least one computer. The memory 9a includes a main memory, such as a random-access memory (RAM), and an auxiliary memory, such as a hard disk drive (HDD) or a solid state drive (SSD). Examples of the arithmetic device 9b include a CPU (central processing unit) and a GPU (graphic processing unit). However, the specific configuration of the operation controller 9 is not limited to these examples.

Polishing of the wafer W is performed as follows. The operation controller 9 instructs the table motor 6, the polishing head 1, and the polishing-liquid supply nozzle 5 to supply the polishing liquid onto the polishing surface 2a of the polishing pad 2 on the polishing table 3, while rotating the polishing table 3 and the polishing head 1 in directions indicated by arrows in FIG. 1. The wafer W is pressed against the polishing surface 2a of the polishing pad 2 by the polishing head 1 in the presence of the polishing liquid between the polishing pad 2 and the wafer W, while the wafer W is being rotated by the polishing head 1. The surface of the wafer W is polished by a chemical action of the polishing liquid and mechanical action(s) of abrasive grains contained in the polishing liquid and/or the polishing pad 2.

Next, the polishing-head system 4 having the polishing head 1 will be described. FIG. 2 is a cross-sectional view of an embodiment of the polishing-head system 4. As shown in FIG. 2, the polishing-head system 4 includes the polishing head 1 having an elastic membrane 34 forming a plurality of pressure chambers 25A, 25B, 25C, and 25D, gas delivery lines F1, F2, F3, and F4 that communicates with the plurality of pressure chambers 25A, 25B, 25C, and 25D, respectively, flow-rate control valves FC1, FC2, FC3, and FC4 coupled to the gas delivery lines F1, F2, F3, and F4, respectively, and a system controller 50 configured to control operations of the flow-rate control valves FC1, FC2, FC3, and FC4.

The system controller 50 includes a memory 50a storing programs therein, an arithmetic device 50b configured to perform arithmetic operations according to instructions included in the programs, and an input device 50c having buttons, a keyboard, or the like. The system controller 50 is composed of at least one computer. The memory 50a includes a main memory, such as a random-access memory (RAM), and an auxiliary memory, such as a hard disk drive (HDD) or a solid state drive (SSD). Examples of the arithmetic device 50b include a CPU (central processing unit) and a GPU (graphic processing unit). However, the specific configuration of the system controller 50 is not limited to these examples. In one embodiment, the system controller 50 and the operation control unit 9 may be configured integrally.

The polishing head 1 includes a carrier 31 fixed to the end of the polishing-head shaft 11, an elastic membrane 34 attached to a lower portion of the carrier 31, and a retainer ring 32 arranged below the carrier 31. The retainer ring 32 is arranged around the elastic membrane 34. The retainer ring 32 is an annular structure configured to retain the wafer W so as to prevent the wafer W from being ejected from the polishing head 1 during polishing of the wafer W.

The elastic membrane 34 includes a contact portion 35 having a contact surface 35a which is contactable with an upper surface of the wafer W, and inner wall portions 36a, 36b, 36c and an outer wall portion 36d coupled to the contact portion 35. The contact portion 35 has substantially the same size and the same shape as those of the upper surface of the wafer W. The inner wall portions 36a, 36b, and 36c and the outer wall portion 36d are endless walls concentrically arranged. The outer wall portion 36d is located outwardly of the inner wall portions 36a, 36b, and 36c, and is arranged so as to surround the inner wall portions 36a, 36b, and 36c. In this embodiment, three inner wall portions 36a, 36b, and 36c are provided, while the configuration of the polishing head 1 is not limited to this embodiment. In one embodiment, two inner wall portions may be provided, or four or more inner wall portions may be provided.

The plurality of (four in this embodiment) pressure chambers 25A, 25B, 25C, and 25D are located between the elastic membrane 34 and the carrier 31. The pressure chambers 25A, 25B, 25C, and 25D are formed by the contact portion 35 of the elastic membrane 34, the inner wall portions 36a, 36b, and 36c, and the outer wall portion 36d. The pressure chamber 25A located at the center of the elastic membrane 34 is circular, while the other pressure chambers 25B, 25C, and 25D are annular. The pressure chambers 25A, 25B, 25C, and 25D are arranged concentrically. In this embodiment, the polishing head 1 has the four pressure chambers 25A to 25D, while in one embodiment, the polishing head 1 may have an elastic membrane 34 having three pressure chambers, or five or more pressure chambers.

An annular membrane (rolling diaphragm) 37 is arranged between the carrier 31 and the retainer ring 32. A pressure chamber 25E is formed inside the membrane 37. Gas delivery lines F1, F2, F3, F4, and F5 are coupled to the pressure chambers 25A, 25B, 25C, 25D, and 25E, respectively. The gas delivery lines F1, F2, F3, F4 and F5 extend through a rotary joint 40 attached to the polishing-head shaft 11.

The gas delivery lines F1, F2, F3, F4, and F5 are coupled to a compressed-gas source (not shown) as a utility supply source provided in a factory where the polishing apparatus is installed. Compressed gas, such as compressed air, is supplied to the pressure chambers 25A, 25B, 25C, 25D, and 25E through the gas delivery lines F1, F2, F3, F4, and F5, respectively.

The flow-rate control valves FC1, FC2, FC3, FC4, FC5 and pressure regulators Ra1, Ra2, Ra3, Ra4, Ra5 are coupled to the gas delivery lines F1, F2, F3, F4, F5, respectively. The flow-rate control valves FC1 to FC5 are arranged downstream of the pressure regulators Ra1 to Ra5 in flow direction of the compressed gas. The compressed gas from the compressed-gas supply source is supplied into the pressure chambers 25A to 25E independently through the pressure regulators Ra1 to Ra5 and the flow-rate control valves FC1 to FC5. The pressure regulators Ra1 to Ra5 are configured to regulate pressures of the compressed gas in the pressure chambers 25A to 25E. The flow-rate control valves FC1 to FC5 are configured to regulate flow rates of the compressed gas supplied into the pressure chambers 25A to 25E. The flow rate represents an amount of fluid flowing per unit time.

The pressure regulators Ra1 to Ra5 and the flow-rate control valves FC1 to FC5 are electrically coupled to the system controller 50. The operations of the pressure regulators Ra1 to Ra5 and the flow-rate control valves FC1 to FC5 are controlled by the system controller 50. The system controller 50 transmits individual target pressure values of the pressure chambers 25A to 25E to the corresponding pressure regulators Ra1 to Ra5, and the pressure regulators Ra1 to Ra5 operate so as to maintain the pressures in the pressure chambers 25A to 25E at the corresponding target pressure values.

The pressure regulators Ra1 to Ra5 can change the internal pressures of the pressure chambers 25A to 25E independently of each other. Therefore, the polishing head 1 can independently regulate polishing pressures on four corresponding regions of the wafer W (i.e., a central portion, an inner intermediate portion, an outer intermediate portion, and an edge portion) and a pressing force of the retainer ring 32 against the polishing surface 2a of the polishing pad 2. For example, the polishing head 1 can press different regions of the surface of the wafer W against the polishing surface 2a of the polishing pad 2 with different polishing pressures. Therefore, the polishing head 1 can control a film-thickness profile of the wafer W to achieve a target film-thickness profile.

Although not shown, each of the flow-rate control valves FC1 to FC5 includes a variable valve whose opening degree can be changed, an actuator configured to drive the variable valve, and a flow meter configured to measure the flow rate of the fluid passing through the variable valve. The system controller 50 instructs the flow-rate control valves FC1 to FC5 to supply the compressed gas at set flow rates to the pressure chambers 25A to 25E through the flow-rate control valves FC1 to FC5. More specifically, the system controller 50 sends command signals indicating the set flow rates to the flow-rate control valves FC1 to FC5, so that the flow-rate control valves FC1 to FC5 operates to deliver the compressed air at the set flow rates to the pressure chambers 25A to 25E.

Vacuum lines Lb1, Lb2, Lb3, Lb4, and Lb5 are coupled to the gas delivery lines F1, F2, F3, F4, and F5, respectively, at positions upstream of the rotary joint 40. Vacuum valves Vb1, Vb2, Vb3, Vb4, and Vb5 are attached to the vacuum lines Lb1, Lb2, Lb3, Lb4, and Lb5, respectively.

When the vacuum valves Vb1 to Vb5 are opened with no supply of the compressed gas, the compressed gas in the pressure chambers 25A to 25E is transferred from the pressure chambers 25A to 25E through the gas delivery lines F1 to F5 and the vacuum lines Lb1 to Lb5 to the exterior of the polishing-head system 4, and negative pressures are formed in the pressure chambers 25A to 25E. Although not shown, the pressure chambers 25A to 25E may be coupled to atmospheric vent lines.

When the wafer W is pressed against the polishing surface 2a of the polishing pad 2 by the polishing head 1 during polishing of the wafer W, the flow rate control by the flow-rate control valves FC1 to FC5 is not performed, while pressure control is performed by the pressure regulators Ra1 to Ra5. As described above, since each flow-rate control valve has the flow meter, the flow-rate control valves FC1 to FC5 are used to measure the flow rates of the compressed air supplied to the pressure chambers 25A to 25E during polishing of the wafer W. The measured values of the flow rates are transmitted from the flow-rate control valves FC1 to FC5 to the system controller 50, and the flow rates of the compressed air are monitored by the system controller 50.

On the other hand, when the polished wafer W is to be released from the polishing head 1, the pressure regulators Ra1 to Ra5 do not perform the pressure control, while the flow-rate control valves FC1 to FC5 perform the flow-rate control. Specifically, the system controller 50 instructs the flow-rate control valves FC1 to FC4 to regulate the flow rates of the compressed air supplied to the pressure chambers 25A to 25D. More specifically, as shown in FIG. 3, the system controller 50 controls the operations of the flow-rate control valves FC1, FC2, FC3, and FC4 such that the compressed gas is supplied through the flow-rate control valves FC1, FC2, FC3, and FC4 to the pressure chambers 25A, 25B, 25C, and 25D at flow rates FR1, FR2, FR3, and FR4, respectively.

In this embodiment, volumes of the pressure chambers 25A to 25D are different. More specifically, the volume of the pressure chamber 25A is larger than the volume of the pressure chamber 25B, the volume of the pressure chamber 25B is larger than the volume of the pressure chamber 25C, and the volume of the pressure chamber 25C is larger than the volume of the pressure chamber 25D. The flow rates FR1, FR2, FR3, and FR4 of the compressed gas differ according to the volumes of the pressure chambers 25A to 25D. Specifically, the larger the volume of the pressure chamber, the higher the flow rate of compressed air supplied. In this embodiment, the flow rate FR1 is higher than the flow rate FR2, the flow rate FR2 is higher than the flow rate FR3, and the flow rate FR3 is higher than the flow rate FR4. Sizes of arrows of the symbols FR1, FR2, FR3, and FR4 shown in FIG. 3 represent magnitudes of the flow rates.

In this way, the flow rates FR1 to FR4 of the compressed gas differ according to the volumes of the pressure chambers 25A to 25D, so that the pressure chambers 25A to 25D can be inflated to curve the contact surface (lower surface) 35a of the elastic membrane 34 downward. In particular, the flow-rate control of the compressed air can inflate the elastic membrane 34 into a desired shape within a limited time. As shown in FIG. 3, the center of the wafer W contacts the contact surface (lower surface) 35a of the elastic membrane 34, and the edge portion of the wafer W is separated from the elastic membrane 34. Release nozzles 51 emit release gas (e.g., an inert gas, such as nitrogen gas) into the gap between the edge portion of the wafer W and the elastic membrane 34. As a result, the wafer W is released from the polishing head 1 and supported on a workpiece transfer device 52.

The flow-rate control valves FC1 to FC4 regulate the flow rates of the compressed gas supplied to the pressure chambers 25A to 25D, so that the downwardly curved shape as shown in FIG. 3 can be stably and quickly formed. As a result, the wafer W can be released from the polishing head 1 with a small amount of release gas, and drying of the wafer W caused by the release gas can be prevented.

The system controller 50 is configured to calculate cumulative values CV1, CV2, CV3, and CV4 of the flow rates FR1, FR2, FR3, and FR4 while the compressed gas is being supplied to the pressure chambers 25A, 25B, 25C, and 25D at the flow rates FR1, FR2, FR3, and FR4. The system controller 50 allows for the supply of the compressed gas into the pressure chambers 25A, 25B, 25C, and 25D at the flow rates FR1, FR2, FR3, FR4 until the cumulative values CV1, CV2, CV3, CV4 of the flow rates FR1, FR2, FR3, FR4 reach corresponding four target flow-rate cumulative values. The shape of each pressure chamber after the inflation is approximately determined by the cumulative value of the flow rate. Therefore, the elastic membrane 34 can be inflated into a desired shape.

In one embodiment, the system controller 50 may calculate the flow rates FR1, FR2, FR3, and FR4 of the compressed gas to be supplied to the pressure chambers 25A, 25B, 25C, and 25D by dividing the plurality of target flow-rate cumulative values corresponding to the pressure chambers 25A, 25B, 25C, and 25D by a preset operating time. For example, the system controller 50 calculates the flow rate FR1 of the compressed gas to be supplied to the pressure chamber 25A by dividing the target flow-rate cumulative value for the pressure chamber 25A by a preset operating time. Similarly, the system controller 50 can calculate the flow rates FR2, FR3, and FR4 of compressed gas to be supplied to the pressure chambers 25B, 25C, and 25D.

As shown in FIG. 3, the system controller 50 instructs the flow-rate control valves FC1, FC2, FC3, and FC4 to supply the compressed gas to the pressure chambers 25A, 25B, 25C, and 25D at the calculated flow rates FR1, FR2, FR3, and FR4. The preset operating time may be the same for the pressure chambers 25A, 25B, 25C, and 25D, or may be different for the pressure chambers 25A, 25B, 25C, and 25D.

A user may input the target flow-rate cumulative values corresponding to the pressure chambers 25A, 25B, 25C, and 25D and the operation time to the system controller 50 via the input device 50c. The system controller 50 can calculate the flow rates FR1, FR2, FR3, and FR4 of the compressed gas to be supplied to the pressure chambers 25A, 25B, 25C, and 25D based on the target flow-rate cumulative values and the operation time that have been input to the system controller 50.

In one embodiment, when the elastic membrane 34 is inflated with the compressed air in order to release the wafer W from the polishing head 1, the system controller 50 may instruct the flow-rate control valves FC1 to FC4 to change the flow rates FR1, FR2, FR3, and FR4 of the compressed air. For example, the system controller 50 instructs the flow-rate control valves FC1 to FC4 to increase the flow rates FR1, FR2, FR3, and FR4 of the compressed air. Such operation of increasing the flow rates FR1, FR2, FR3, and FR4 can quickly inflate the pressure chambers 25A to 25D into a desired shape, and can improve a throughput of the polishing apparatus. Furthermore, since the release operation is performed in a shorter time, drying of the polished wafer due to the release gas can be prevented. The flow rates FR1 to FR4 may be increased stepwise (for example, in two steps), or may be increased linearly or curvilinearly.

In one embodiment, the system controller 50 may instruct the flow-rate control valves FC1 to FC4 to reduce the flow rates FR1, FR2, FR3, and FR4 of the compressed air. For example, the system controller 50 instructs the flow-rate control valves FC1 to FC4 to reduce the flow rates FR1, FR2, FR3, and FR4 from set flow rates for rapid inflation to set flow rates for normal operation. The set flow rates for rapid inflation and the set flow rates for normal operation are predetermined flow rates necessary for the rapid inflation and the normal operation. In this example as well, the pressure chambers 25A to 25D can be rapidly inflated to a desired shape.

When the wafer W to be polished is held by the polishing head 1, the system controller 50 instructs the flow-rate control valves FC1 to FC4 to regulate the flow rates of the compressed air supplied to the pressure chambers 25A to 25D as well. More specifically, as shown in FIG. 4, before the polishing head 1 holds the wafer W on the workpiece transfer device 52, the system controller 50 instructs the flow-rate control valves FC1 to FC4 to inflate the elastic membrane 34. Then, as shown in FIG. 5, the polishing head 1 is lowered by the vertical movement mechanism 18 (see FIG. 1) until the elastic membrane 34 contacts the upper surface of the wafer W on the workpiece transfer device 52, so that the downwardly curved elastic membrane 34 can remove liquid from the upper surface of the wafer W to be polished.

As shown in FIG. 4, the system controller 50 controls the operations of the flow-rate control valves FC1, FC2, FC3, and FC4 to cause the compressed gas to flow through the flow-rate control valves FC1, FC2, FC3, and FC4 at flow rates of FR5, FR6, FR7, and FR8 into the pressure chambers 25A, 25B, 25C, and 25D. The flow rates FR5, FR6, FR7, and FR8 of the compressed gas differ according to the volumes of the pressure chambers 25A to 25D. Specifically, the larger the volume of the pressure chamber, the higher the flow rate of compressed air supplied. In this embodiment, the flow rate FR5 is higher than the flow rate FR6, the flow rate FR6 is higher than the flow rate FR7, and the flow rate FR7 is higher than the flow rate FR8. Sizes of arrows of the symbols FR5, FR6, FR7, and FR8 shown in FIG. 3 represent magnitudes of the flow rates.

The system controller 50 is configured to calculate cumulative values CV5, CV6, CV7, and CV8 of the flow rates FR5, FR6, FR7, and FR8 while the compressed gas is being supplied to the pressure chambers 25A, 25B, 25C, and 25D at the flow rates FR5, FR6, FR7, and FR8. The system controller 50 allows for the supply of the compressed gas into the pressure chambers 25A, 25B, 25C, and 25D at the flow rates FR5, FR6, FR7, and FR8 until the cumulative values CV5, CV6, CV7, and CV8 of the flow rates FR5, FR6, FR7, and FR8 reach corresponding four target flow-rate cumulative values. The shape of each pressure chamber after the inflation is approximately determined by the cumulative value of the flow rate. Therefore, the elastic membrane 34 can be inflated into a desired shape.

In one embodiment, the system controller 50 may calculate the flow rates FR5, FR6, FR7, and FR8 of the compressed gas to be supplied to the pressure chambers 25A, 25B, 25C, and 25D by dividing the plurality of target flow-rate cumulative values corresponding to the pressure chambers 25A, 25B, 25C, and 25D by a preset operating time. For example, the system controller 50 calculates the flow rate FR5 of the compressed gas to be supplied to the pressure chamber 25A by dividing the target flow-rate cumulative value for the pressure chamber 25A by a preset operating time. Similarly, the system controller 50 can calculate the flow rates FR6, FR7, and FR8 of compressed gas to be supplied to the pressure chambers 25B, 25C, and 25D.

As shown in FIGS. 4 and 5, the system controller 50 instructs the flow-rate control valves FC1, FC2, FC3, and FC4 to supply the compressed gas to the pressure chambers 25A, 25B, 25C, and 25D at the calculated flow rates FR5, FR6, FR7, and FR8. The preset operating time may be the same for the pressure chambers 25A, 25B, 25C, and 25D, or may be different for the pressure chambers 25A, 25B, 25C, and 25D.

A user may input the target flow-rate cumulative values corresponding to the pressure chambers 25A, 25B, 25C, and 25D and the operation time to the system controller 50 via the input device 50c. The system controller 50 can calculate the flow rates FR5, FR6, FR7, and FR8 of the compressed gas to be supplied to the pressure chambers 25A, 25B, 25C, and 25D based on the target flow-rate cumulative values and the operation time that have been input to the system controller 50.

In one embodiment, when the elastic membrane 34 is inflated with the compressed air in order to remove the liquid from the wafer W by the elastic membrane 34, the system controller 50 may instruct the flow-rate control valves FC1 to FC4 to change the flow rates FR5, FR6, FR7, and FR8 of the compressed air. For example, the system controller 50 instructs the flow-rate control valves FC1 to FC4 to increase the flow rates FR5, FR6, FR7, and FR8 of the compressed air. Such operation of increasing the flow rates FR5, FR6, FR7, and FR8 can quickly inflate the pressure chambers 25A to 25D into a desired shape, and can improve a throughput of the polishing apparatus. The flow rates FR5 to FR8 may be increased stepwise (for example, in two steps), or may be increased linearly or curvilinearly.

In one embodiment, the system controller 50 may instruct the flow-rate control valves FC1 to FC4 to reduce the flow rates FR5, FR6, FR7, and FR8 of the compressed air. For example, the system controller 50 instructs the flow-rate control valves FC1 to FC4 to reduce the flow rates FR5, FR6, FR7, and FR8 from set flow rates for rapid inflation to set flow rates for normal operation. The set flow rates for rapid inflation and the set flow rates for normal operation are predetermined flow rates necessary for the rapid inflation and the normal operation. In this example as well, the pressure chambers 25A to 25D can be rapidly inflated to a desired shape.

In one embodiment, when the wafer W is being pressed against the polishing pad 2 by the polishing head 1 during polishing of the wafer W, the flow-rate control valves FC1 to FC4 measure the flow rates of the compressed gas supplied to the pressure chambers 25A to 25D. During polishing of the wafer W, the flow-rate control valves FC1 to FC4 measure the flow rates of the compressed gas supplied to the pressure chambers 25A to 25D, but do not regulate the flow rates of the compressed gas.

FIG. 6 is a graph showing an example of a temporal change in the flow rate of compressed gas supplied to the pressure chamber 25A when the wafer W is being pressed against the polishing pad 2 by the polishing head 1 during polishing of the wafer W. The pressure regulators Ra1, Ra2, Ra3, and Ra4 shown in FIG. 2 regulate the pressures of the compressed gas in the pressure chambers 25A to 25D. With such pressure regulating operations, the flow rate of the compressed gas supplied to the pressure chamber 25A changes with time as shown in FIG. 6. Although not shown, the flow rates of the compressed gas supplied to the pressure chambers 25B to 25D also change with time in the same way.

The system controller 50 is configured to calculate polishing flow-rate cumulative values PV1, PV2, PV3, and PV4 which are cumulative values of the flow rates measured during polishing of the wafer, and detect or determine a malfunction of the elastic membrane 34 or a polishing abnormality of the wafer W based on a change in at least one of the polishing flow-rate cumulative values PV1, PV2, PV3, and PV4. The polishing flow-rate cumulative values PV1, PV2, PV3, and PV4 correspond to the pressure chambers 25A, 25B, 25C, and 25D, respectively.

More specifically, when at least one of the polishing flow-rate cumulative values PV1, PV2, PV3, and PV4 is out of an allowable range, the system controller 50 detects a malfunction of the elastic membrane 34 or a polishing abnormality of the wafer W. For example, if the polishing flow-rate cumulative value PV1 falls outside the allowable range each time a wafer is polished, the system controller 50 determines that there is a malfunction of the elastic membrane 34 or the pressure regulator Ra1. In another example, when the polishing flow-rate cumulative value PV1 obtained during polishing of a certain wafer among a plurality of wafers is out of the allowable range, the system controller 50 determines that a polishing abnormality has occurred for that wafer, or determines that there is a defect of that wafer itself (for example, excessive variation in film thickness of the wafer, or a crack in the wafer).

In one embodiment, the allowable range is a range that includes an average of polishing flow-rate cumulative values obtained from polishing of wafers in the past. A plurality of allowable ranges are provided for the polishing flow-rate cumulative values PV1, PV2, PV3, and PV4, respectively.

The previous description of embodiments is provided to enable a person skilled in the art to make and use the present invention. Moreover, various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles and specific examples defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the embodiments described herein but is to be accorded the widest scope as defined by limitation of the claims.

METHOD OF INFLATING ELASTIC MEMBRANE OF POLISHING HEAD, AND POLISHING HEAD SYSTEM

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