Grinding device

Abstract

This invention provides a grinding apparatus capable of efficiently monitoring film thickness on a wide variety of materials to be ground. The grinding apparatus includes a grinding head, a grinding table, and a film thickness measurement system. The film thickness measurement system includes multiple sensor heads and a control unit. The multiple sensor heads are disposed on the grinding table, and each sensor head is composed of an eddy current sensor. The control unit includes: an oscillator that generates a common clock signal for driving the eddy current sensors; and multiple control circuits, each corresponding to one of the multiple sensor heads. Each control circuit is configured to generate a drive signal applied to the eddy current sensor of that sensor head based on the clock signal from the oscillator, and to process the measurement signal received from the eddy current sensor of that sensor head.

Description

Technical Field

[0001] This invention relates to a grinding apparatus. Background Technology

[0002] Conventionally, polishing apparatuses are used for polishing objects such as semiconductor substrates. A polishing apparatus includes a polishing table on which an polishing pad is mounted and a polishing head on which the substrate to be polished is mounted. In the polishing apparatus, polishing fluid is supplied to the polishing pad, and at least one of the polishing table and the polishing head is rotated while the polishing pad and the substrate are in contact, thereby polishing the substrate.

[0003] A film thickness sensor is provided on the polishing table to monitor the amount of polishing applied to a substrate or a film on the substrate. As the film thickness sensor, an eddy current sensor capable of measuring the thickness of a conductive film on a substrate can be used (see, for example, Patent Document 1).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2011-23579

[0007] Eddy current sensors typically measure sensitivity changes based on the material and thickness of the membrane being measured. Preferably, an eddy current sensor with optimal sensor characteristics is used based on the material and thickness of the membrane being measured. Summary of the Invention

[0008] The present invention was made in view of the above-mentioned problems, and one of its objectives is to provide a grinding apparatus capable of efficiently monitoring film thickness for a wide variety of types of workpieces.

[0009] According to one embodiment, a grinding apparatus is provided for grinding a workpiece, comprising: a grinding head configured to mount the workpiece; a grinding table configured to be opposite to the workpiece mounted on the grinding head and rotatable; and a film thickness measuring system for measuring the thickness of a conductive film on the workpiece ground by the grinding apparatus, the film thickness measuring system comprising a plurality of sensor heads and a control unit, the plurality of sensor heads being disposed on the grinding table, each sensor head being configured as an eddy current sensor, the control unit comprising: an oscillator generating a common clock signal for driving the eddy current sensor; and a plurality of control circuits respectively disposed corresponding to the plurality of sensor heads, each control circuit being configured to generate a drive signal applied to the eddy current sensor of the sensor head based on the clock signal from the oscillator, and to process the measurement signal received from the eddy current sensor of the sensor head.

[0010] In the above embodiments, the eddy current sensor in one part of the plurality of sensor heads may have different sensor characteristics than the eddy current sensor in another part of the plurality of sensor heads.

[0011] In the above embodiments, the eddy current sensor in one part of the plurality of sensor heads and the eddy current sensor in another part of the plurality of sensor heads may be sensors corresponding to different membrane types.

[0012] In the above embodiments, the eddy current sensor in one part of the plurality of sensor heads and the eddy current sensor in another part of the plurality of sensor heads may be sensors corresponding to different film thicknesses.

[0013] In the above embodiments, the eddy current sensor in one part of the plurality of sensor heads and the eddy current sensor in another part of the plurality of sensor heads may be sensors with different spatial resolutions.

[0014] In the above embodiments, the control unit may include a switching unit that switches the sensor head in such a way that an eddy current sensor with optimal sensor characteristics is used according to the grinding scheme. Attached Figure Description

[0015] Figure 1 This is a schematic diagram illustrating the structure of a grinding apparatus according to one embodiment of the present invention.

[0016] Figure 2 This is a schematic diagram showing the structure of a film thickness measurement system mounted on a grinding apparatus according to one embodiment of the present invention.

[0017] Figure 3 This is a schematic diagram showing the structure of a film thickness measurement system based on conventional methods.

[0018] Figure 4A This is a diagram illustrating an example of the structure of multiple sensor heads in a film thickness measurement system based on one embodiment of the present invention.

[0019] Figure 4B This is a diagram illustrating an example of the structure of multiple sensor heads in a film thickness measurement system based on one embodiment of the present invention.

[0020] Figure 5 This is a diagram illustrating an example of a configuration of multiple sensor heads arranged toward a grinding stage in a film thickness measurement system based on one embodiment of the present invention.

[0021] Symbol Explanation

[0022] 10 Grinding device

[0023] 20 Film Thickness Measurement System

[0024] 30 Grinding table

[0025] 31 Grinding Pad

[0026] 311 Grinding surface

[0027] 32 shafts

[0028] 40 Top Ring

[0029] 41A retaining ring

[0030] 41B Top Ring Body

[0031] 42 Top Ring Shaft

[0032] 43 Top ring drive motor

[0033] 50 arms

[0034] 52 arm shaft

[0035] 53-arm drive motor

[0036] 61 Rotating Cylinder

[0037] 62 Synchronous Belt Pulley

[0038] 63 Synchronous Belt

[0039] 64 Synchronous Belt Pulley

[0040] 80 Eddy Current Sensor (Sensor Head)

[0041] 81 Sensor Coil

[0042] 82 Resistors for Impedance Matching

[0043] 100 Control Unit

[0044] 100A drive circuit

[0045] 100B Detection Circuit

[0046] 110 Oscillator

[0047] 120 Distributor

[0048] 130x Multiplier Circuit

[0049] 140 Phase Shifter

[0050] 150 switching circuit

[0051] 160 Variable Attenuator

[0052] 170 Fixed Amplifier

[0053] 180Ω impedance matching resistor

[0054] 185 Impedance matching resistor

[0055] 190 AD converter

[0056] 195 Signal processing circuit. Detailed Implementation

[0057] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings described below, the same or equivalent constituent elements are labeled with the same symbols and repeated descriptions are omitted.

[0058] Figure 1 This is a schematic diagram showing the structure of a polishing apparatus 10 according to one embodiment of the present invention. As shown, the polishing apparatus 10 includes: a polishing table 30 for holding a polishing pad 31; and a top ring 40 (polishing head) that holds a substrate (wafer Wf) as the object to be polished in a manner opposite to the polishing pad 31 and presses it against the polishing surface of the polishing pad 31.

[0059] The polishing table 30 is connected to a table drive motor (not shown) disposed below it via a table shaft 32. The table drive motor drives the table to rotate, thereby enabling the polishing table 30 to rotate about the axis of the table shaft 32. A polishing pad 31 is attached to the upper surface of the polishing table 30. The surface 311 of the polishing pad 31 forms the polishing surface of the polishing wafer Wf. An polishing slurry supply nozzle (not shown) is provided above the polishing table 30, supplying polishing slurry to the polishing pad 31 on the polishing table 30.

[0060] An eddy current sensor 80 is installed inside the polishing table 30. The eddy current sensor 80 is positioned such that it passes through the center of the wafer Wf when the polishing table 30 rotates during polishing. The eddy current sensor 80 is connected to the control unit 100 via a signal cable 83. The eddy current sensor 80 is configured to induce eddy currents in the conductive film on the surface of the wafer Wf. The eddy current sensor 80 is also configured to receive the impedance change caused by the magnetic field generated by the eddy current and output a signal corresponding to the thickness of the conductive film on the surface of the wafer Wf. The thickness of the conductive film on the surface of the wafer Wf can be determined using the output signal from the eddy current sensor 80. Furthermore, in Figure 1 Only one eddy current sensor 80 is shown in the figure, but it can be represented as follows: Figure 2 or Figure 5 In this way, multiple eddy current sensors 80 are placed inside the grinding table 30.

[0061] The top ring 40 is supported on the arm 50 via a top ring shaft 42. The top ring shaft 42 is movable vertically relative to the arm 50 via a vertical movement mechanism (not shown). The vertical movement of the top ring shaft 42 allows the top ring 40 to be positioned vertically relative to the arm 50. The top ring 40 is configured to hold the wafer Wf on its lower surface. Specifically, as... Figure 1 As shown, the top ring 40 includes: a retaining ring 41A that holds the outer peripheral edge of the wafer Wf so that the wafer Wf does not fly out of the top ring 40; and a top ring body 41B that presses the wafer Wf onto the polishing surface 311.

[0062] A top ring drive motor 43 is fixed to the arm 50 supporting the top ring 40. Additionally, as... Figure 1 As shown, the top ring shaft 42 is connected to the rotating cylinder 61, and the synchronous pulley 62, located on the outer periphery of the rotating cylinder 61, is connected to the synchronous pulley 64, which is located on the top ring drive motor 43, via the synchronous belt 63. Thus, when the top ring drive motor 43 rotates, the rotating cylinder 61 and the top ring shaft 42 rotate as a whole via the synchronous pulley 64, the synchronous belt 63, and the synchronous pulley 62, and the top ring 40 rotates around the axis of the top ring shaft 42.

[0063] The arm 50 is connected to an arm drive motor 53 that is fixed to the arm shaft 52. Driven by the arm drive motor 53, the arm 50 and the top ring 40 supported on the arm 50 can rotate about the axis of the arm shaft 52.

[0064] When the polishing apparatus 10 operates, firstly, at a designated receiving position, the top ring 40 receives and holds the wafer Wf conveyed by a transport mechanism (not shown). The top ring 40, having received the wafer Wf at the receiving position, moves from the receiving position to above the polishing table 30 via the rotation of the arm 50. Next, the top ring shaft 42 and the top ring 40 descend, pressing the wafer Wf onto the polishing surface 311 of the polishing pad 31. Then, the table drive motor and the top ring drive motor 43 rotate, thereby rotating the polishing table 30 and the top ring 40 respectively. Simultaneously, polishing slurry is supplied to the polishing pad 31 from a polishing slurry supply nozzle positioned above the polishing table 30. Thus, the wafer Wf slides into contact with the polishing surface 311 of the polishing pad 31, thereby polishing the surface of the wafer Wf. Alternatively, during the polishing of the wafer Wf, the arm drive motor 53 causes the arm 50 to periodically rotate left and right, thereby causing the top ring 40 to oscillate relative to the polishing pad 31 (i.e., reciprocating motion of the top ring 40 on the polishing pad 31) while polishing.

[0065] Figure 2This is a schematic diagram showing the structure of a film thickness measurement system 20 mounted on a polishing apparatus 10 according to one embodiment of the present invention. The film thickness measurement system 20 is a system for measuring the thickness of a conductive film on a wafer Wf polished by the polishing apparatus 10, and includes multiple sensor heads (eddy current sensors) 80 and a control unit 100 for controlling these multiple sensor heads 80.

[0066] Each of the multiple sensor heads (eddy current sensors) 80 includes a sensor coil 81 and an impedance matching resistor 82. Each sensor head (eddy current sensor) 80 is disposed inside the polishing table 30 as described above. The sensor coil 81 of each sensor head 80 generates a magnetic field based on a drive signal from the control unit 100, thereby inducing eddy currents in the conductive film on the surface of the wafer Wf. Furthermore, it receives the change in circuit impedance caused by these eddy currents and generates a signal corresponding to the thickness of the conductive film on the surface of the wafer Wf.

[0067] The control unit 100 includes a drive circuit 100A and a detection circuit 100B. The drive circuit 100A includes an oscillator 110, a distributor 120, multiple multiplier circuits 130, multiple phase shifters 140, a switching circuit 150, multiple variable attenuators 160, multiple fixed amplifiers (Amp) 170, and multiple impedance matching resistors 180. The detection circuit 100B includes multiple impedance matching resistors 185, multiple analog-to-digital converters (ADCs) 190, and a signal processing circuit 195. The multiplier circuits 130, phase shifters 140, variable attenuators 160, fixed amplifiers 170, impedance matching resistors 180 and 185, and ADCs 190 are respectively configured to correspond to the multiple sensor heads 80.

[0068] The components constituting the drive circuit 100A (oscillator 110, distributor 120, multiplier circuit 130, etc.) can be housed within a frame (e.g., a metal frame). Similarly, the components constituting the detection circuit 100B (signal processing circuit 195, AD converter 190, impedance matching resistor 185) can also be housed within a frame (e.g., a metal frame). All components constituting both the drive circuit 100A and the detection circuit 100B can also be housed within a single frame (e.g., a metal frame).

[0069] Oscillator 110 generates a common clock signal (e.g., a high-frequency signal of 1 MHz) for driving multiple eddy current sensors 80. Distributor 120 distributes the clock signal from oscillator 110 to multiple multiplier circuits 130. Each of the multiple multiplier circuits 130 multiplies the clock signal distributed by distributor 120 to a frequency that corresponds to the operating frequency band of the eddy current sensor 80 corresponding to that multiplier circuit 130. Each phase shifter 140 applies a phase shift to the signal from the corresponding multiplier circuit 130 for synchronous detection.

[0070] The switching circuit 150 is used to select and activate the drive signal for the eddy current sensor 80 actually in use among the plurality of eddy current sensors 80 disposed on the grinding table 30. Specifically, the switching circuit 150 operates in such a way that it supplies a signal from the phase shifter 140 to the variable attenuator 160 corresponding to the actually used eddy current sensor 80, and does not supply a signal from the phase shifter 140 to the variable attenuator 160 corresponding to the unused eddy current sensor 80. The number of drive signals activated can be one or more. The selection of the drive signal can be, for example, based on a pre-prepared scheme.

[0071] One or more drive signals, activated by the switching circuit 150, are adjusted to a predetermined signal strength via the variable attenuator 160 and the fixed amplifier 170, and then supplied to the corresponding eddy current sensor 80. Consequently, in response to the generation of eddy currents in the conductive film of the wafer Wf due to the magnetic field generated by the sensor coil 81 of the eddy current sensor 80, a detection signal corresponding to the thickness of the conductive film is output from the eddy current sensor 80. The signal from the eddy current sensor 80 is input to the signal processing circuit 195 via the AD converter 190. The signal processing circuit 195 calculates the thickness of the conductive film on the surface of the wafer Wf by processing the detection signal from the eddy current sensor 80.

[0072] Figure 3 This is a schematic diagram showing the structure of a conventional film thickness measurement system 21. The film thickness measurement system 21 includes multiple sensor units 80'. Each sensor unit 80' includes a distributor 120, a multiplier circuit 130, a phase shifter 140, a variable amplifier 170, a sensor coil 81, a buffer circuit (Buf) 186, an AD converter 190, and a signal processing circuit 195. Additionally, one of the sensor units 80' also includes an oscillator 110. The elements in the sensor unit 80' are similar to those described above. Figure 2 The elements in the film thickness measurement system 20 are the same.

[0073] exist Figure 3In the film thickness measurement system 21, the elements constituting each sensor unit 80' are housed in a separate frame (e.g., a metal frame) for each sensor unit. Therefore, the signal line 122 used to transmit the clock signal distributed from the distributor 120 to another sensor unit 80' passes outside this frame. Consequently, there is a possibility that noise from the external environment may interfere with the clock signal in the portion of the signal line 122 outside the frame.

[0074] In contrast, in one embodiment of the present invention Figure 2 In the film thickness measurement system 20 with the structure shown, the signal line transmitting the clock signal is prevented from being exposed to external environmental noise. Therefore, the degradation of clock signal quality due to noise intrusion can be avoided, and the accuracy of film thickness measurement in the film thickness measurement system 20 using the eddy current sensor 80 can be improved.

[0075] Furthermore, the sensor head 80 in the film thickness measurement system 20 according to one embodiment of the present invention has fewer components than the sensor unit 80' in the conventional film thickness measurement system 21, and therefore the sensor head 80 is smaller than the sensor unit 80'. Thus, in the film thickness measurement system 20 based on one embodiment of the present invention... Figure 1 In the grinding apparatus 10, more sensor heads (eddy current sensors) 80 can be installed on the grinding table 30.

[0076] Figure 4A and 4B This is a diagram illustrating an example of the structure of a plurality of sensor heads 80 in a film thickness measurement system 20 based on one embodiment of the present invention. Figure 4A In the example, the control unit 100 is connected to a type 1 sensor head 80A, a type 2 sensor head 80B, a type 3 sensor head 80C, and a type 4 sensor head 80D. Each type of sensor head (eddy current sensor) 80A, 80B, 80C, and 80D has different sensor characteristics. Specifically, the type 2 sensor head 80B has sensor characteristics suitable for measuring thicker films of film type 1 (e.g., Cu (copper)). The type 3 sensor head 80C has sensor characteristics suitable for measuring thinner films of film type 1. The type 1 sensor head 80A has the following sensor characteristics: suitable for measuring films of film type 1 with a wide range of thicknesses from thin to thick films, and with high spatial resolution (i.e., small spot diameter of the magnetic field emitted from the sensor coil 81) and excellent detection performance at the film edges. The type 4 sensor head 80D has sensor characteristics suitable for measuring films of film type 2 (e.g., W (tungsten)) with a wide range of thicknesses from thin to thick films.

[0077] According to this Figure 4AWith such a structure of multiple sensor heads 80, the switching circuit 150 can switch the sensor head 80 to be used according to a pre-prepared scheme based on the type of wafer Wf to be ground, thereby enabling flexible measurement of film thickness for a wide variety of types of films.

[0078] exist Figure 4B In this example, the control unit 100 connects three sensor heads 80A of type 1 and two sensor heads 80C of type 3. In this example, multiple sensor heads 80 of the same type are used simultaneously, and the signal processing circuit 195 calculates the film thickness based on the signals from these multiple sensor heads 80, thereby improving the accuracy of the film thickness calculation.

[0079] Figure 5 This diagram illustrates a configuration example of a film thickness measurement system 20 according to an embodiment of the present invention, in which multiple sensor heads 80 are arranged on a polishing table 30. In configuration example 1, one sensor head 80A of type 1 and one sensor head 80B of type 2 are provided on the polishing table 30. In configuration example 2, two sensor heads 80A of type 1 and one sensor head 80C of type 3 are provided on the polishing table 30. In configuration example 3, three sensor heads 80A of type 1 and one sensor head 80B of type 2 are provided on the polishing table 30. Furthermore, in configuration example 3, a pressure sensor 85 can be provided on the polishing table 30. The pressure sensor 85 is used to detect the pressing pressure of the wafer Wf held on the top ring 40 on the polishing table 30. In addition to the pressure sensor 85, a temperature sensor for measuring the temperature of the wafer Wf during polishing can also be provided or replaced by the pressure sensor 85. In configuration example 4, three sensor heads 80A of type 1, one sensor head 80B of type 2, and three sensor heads 80C of type 3 are provided on the polishing table 30. In Configuration Example 5, the polishing stage 30 is equipped with four sensor heads 80A of type 1, four sensor heads 80C of type 3, and four sensor heads 80D of type 4. By providing multiple types of sensor heads 80 (sensor heads 80A, 80B, 80C, 80D) with different sensor characteristics on the polishing stage 30, and by using the switching circuit 150 to appropriately (e.g., according to a pre-prepared scheme based on the wafer Wf to be polished), film thickness measurement can be flexibly performed on a wide variety of wafers Wf.

[0080] The embodiments of the present invention have been described above based on several examples. However, the above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention can, of course, be modified and altered without departing from its spirit, and its equivalents are included. Furthermore, any combination or omission of the components described in the specification and the scope of protection claimed by the present invention can be made within the scope that solves at least a portion of the above-mentioned problems or achieves at least a portion of the effects.

Claims

1. A grinding apparatus for grinding a workpiece, characterized in that, have: A grinding head configured to mount the workpiece being ground; A grinding table, configured to face the workpiece mounted on the grinding head, and configured to be rotatable; as well as A film thickness measurement system is used to measure the thickness of the conductive film on the workpiece being ground by the grinding device. The film thickness measurement system includes: Multiple sensor heads are disposed on the grinding table, and each sensor head is composed of an eddy current sensor; and Control unit The control unit includes: An oscillator that generates a common clock signal for driving the eddy current sensor; and Multiple control circuits are respectively provided corresponding to the multiple sensor heads, and each control circuit is configured to generate a drive signal applied to the eddy current sensor of the sensor head based on the clock signal from the oscillator, and process the measurement signal received from the eddy current sensor of the sensor head.

2. The grinding apparatus according to claim 1, characterized in that, The eddy current sensor in one part of the plurality of sensor heads has different sensor characteristics than the eddy current sensor in another part of the plurality of sensor heads.

3. The grinding apparatus according to claim 2, characterized in that, The eddy current sensor in one part of the plurality of sensor heads and the eddy current sensor in another part of the plurality of sensor heads are sensors corresponding to different membrane types.

4. The grinding apparatus according to claim 2, characterized in that, The eddy current sensor in one part of the plurality of sensor heads and the eddy current sensor in another part of the plurality of sensor heads are sensors corresponding to different film thicknesses.

5. The grinding apparatus according to claim 2, characterized in that, The eddy current sensor in one part of the plurality of sensor heads and the eddy current sensor in another part of the plurality of sensor heads are sensors with different spatial resolutions.

6. The grinding apparatus according to any one of claims 2 to 5, characterized in that, The control unit includes a switching unit that switches the sensor head in such a way that the eddy current sensor with the best sensor characteristics is used according to the grinding scheme.

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