Polishing endpoint detection device and cmp device

Abstract

[Problem] To provide a polishing endpoint detection device and a CMP device which can detect the film thickness of a workpiece under polishing with high accuracy in a short time. [Solution] A polishing endpoint detection device (10) includes a fixed-side barrel (25) disposed outside a platen (2), a rotating-side barrel (26) disposed on the platen (2) and transmitting light in a wireless manner with the fixed-side barrel (25), and a sensor head (22) housed in an observation hole (8) formed in the platen (2) and the polishing pad (5) and connected with the rotating-side barrel (26) via a second optical fiber (27) to irradiate measuring light toward a workpiece (W) when the workpiece (W) passes through the observation hole (8) and receive reflected light from the workpiece (W).

Description

Technical Field

[0001] This invention relates to a grinding endpoint detection device and a CMP device. Background Technology

[0002] In the field of semiconductor manufacturing, CMP (Chemical Mechanical Polishing) devices are known to planarize semiconductor silicon wafers (hereinafter referred to as "workpieces") by grinding.

[0003] The grinding apparatus described in Patent Document 1 is a grinding apparatus that utilizes chemical mechanical polishing (CMP) technology. This CMP apparatus presses a workpiece mounted on a grinding head onto a grinding pad to grind the workpiece. Furthermore, a sensor head positioned below the pressure plate illuminates the workpiece through an observation hole each time the pressure plate rotates, and detects the grinding endpoint of the workpiece based on the intensity spectrum of the reflected light.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: JP 2017-52027 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] However, in the grinding apparatus described in Patent Document 1, since the film thickness is measured only at one point within the workpiece each time the pressure plate rotates, therefore... Figure 4 As shown, by moving the grinding head in the horizontal direction d1, the measuring position mp of the scanning sensor head 101 is measured within the workpiece 100 rotating along the rotation direction d2. In order to detect the grinding endpoint with good measurement accuracy, the required number of measuring points are measured. Figure 4 The film thickness is measured at 8 locations (in the middle), therefore, film thickness measurement requires a long time.

[0009] Therefore, in order to detect the film thickness of a workpiece during grinding with high precision in a short time, a technical problem has arisen that needs to be solved, and the purpose of this invention is to solve this problem.

[0010] Technical solutions for solving the problem

[0011] To achieve the above objectives, the grinding apparatus of the present invention is a grinding endpoint detection device, which measures the film thickness of a workpiece being ground on a grinding pad pressed against a pressure plate, and detects the grinding endpoint based on the film thickness of the workpiece. The grinding endpoint detection device includes: a fixed-side mirror tube disposed outside the pressure plate and connected to a light source and a beam splitter via a first optical fiber; a rotating-side mirror tube disposed on the pressure plate and wirelessly transmitting light between it and the fixed-side mirror tube; and a sensing head housed in an observation hole formed in the pressure plate and the grinding pad, and connected to the rotating-side mirror tube via a second optical fiber. When the workpiece passes through the observation hole, the sensing head irradiates measurement light toward the workpiece and receives reflected light from the workpiece.

[0012] In addition, the CMP apparatus of the present invention includes the above-described grinding endpoint detection device.

[0013] Invention Effects

[0014] This invention can detect the film thickness of a workpiece during grinding with high precision in a short time. Attached Figure Description

[0015] Figure 1 A perspective view of the CMP apparatus related to the first embodiment of the present invention is shown schematically.

[0016] Figure 2 A longitudinal sectional view schematically showing the main parts of a CMP apparatus;

[0017] Figure 3 This is a schematic diagram illustrating the scanning of the film thickness measurement position within the workpiece during one rotation of the pressure plate;

[0018] Figure 4 This is a schematic diagram illustrating the situation in an existing CMP apparatus where the grinding head moves horizontally to scan the film thickness measurement position within the workpiece. Detailed Implementation

[0019] One embodiment of the present invention will be described with reference to the accompanying drawings. Furthermore, when referring to the number, value, quantity, range, etc., of the constituent elements, they are not limited to that specific quantity, except where specifically stated or clearly limited in principle to a particular quantity; they may be more than or less than that specific quantity.

[0020] In addition, when referring to the shape and positional relationship of constituent elements, etc., except for cases that are specifically stated or that are obviously not the case in principle, it includes cases that are substantially similar or analogous to that shape, etc.

[0021] Furthermore, the accompanying drawings may exaggerate features by enlarging them for easier understanding, and the size ratios of the constituent elements may not be the same as actual dimensions. Additionally, in sectional views, some section lines of the constituent elements are sometimes omitted to facilitate understanding of their cross-sectional structure.

[0022] Figure 1 The image shows a perspective view of a CMP apparatus 1 according to one embodiment of the present invention. The CMP apparatus 1 grinds one side of a workpiece W to make it flat. The CMP apparatus 1 includes a pressure plate 2 and a grinding head 3. The workpiece W is, for example, a silicon wafer, but is not limited thereto.

[0023] The pressure plate 2 is formed in the shape of a disc and is connected to a rotating shaft 2a disposed below the pressure plate 2. The rotating shaft 2a is rotated by the drive of the motor 4, thereby causing the pressure plate 2 to... Figure 1 Rotate in the direction of arrow D1. An abrasive pad 5 is attached to the top of the pressure plate 2, and a mixture of abrasive and chemical, namely CMP slurry, is supplied to the abrasive pad 5 through a nozzle not shown in the figure.

[0024] The grinding head 3 is formed with a diameter smaller than that of the pressure plate 2 and is connected to a rotating shaft 3a disposed above the grinding head 3. The rotating shaft 3a is rotated by a motor (not shown in the figure), thereby causing the grinding head 3 to... Figure 1 The grinding head 3 rotates in the direction of arrow D2. The grinding head 3 is configured to move vertically and horizontally via a head moving mechanism (not shown in the figure). When grinding the workpiece W, the grinding head 3 descends and presses the workpiece W onto the grinding pad 5.

[0025] The operation of CMP device 1 is controlled by controller 6. Controller 6 controls the constituent elements of CMP device 1. Controller 6 is, for example, a computer, consisting of a CPU, memory, etc. Furthermore, the function of controller 6 can be implemented through software control or through hardware operation.

[0026] Secondly, according to Figure 2 The main parts of the CMP apparatus 1 will be described. The grinding head 3 includes a chuck 7 that is connected to and rotates together with the rotating shaft 3a.

[0027] A chuck 7 is provided at the lower part of the grinding head 3. The chuck 7 has an alumina chuck stage 7a. The chuck 7 is connected to a vacuum source and a compressed air source (not shown in the figure). By activating the vacuum source, the workpiece W is attracted and held on the holding surface 7b of the chuck 7. Alternatively, by activating the compressed air source, compressed air is supplied between the holding surface 7b and the workpiece W to release the workpiece W from the attraction.

[0028] With this structure, the CMP apparatus 1 grinds the workpiece W in the following sequence: First, with the workpiece W facing downwards, it is held by the grinding head 3. Next, the grinding head 3 moves onto the pressure plate 2, and both the pressure plate 2 and the grinding head 3 rotate in the same direction. Then, while supplying slurry to the grinding pad 5, the grinding head 3 presses the workpiece W onto the grinding pad 5 to grind it. Furthermore, when the grinding endpoint detection device 10 (described later) detects the grinding endpoint of the workpiece W, the controller 6 stops the pressure plate 2 and the grinding head 3, and the grinding of the workpiece W ends.

[0029] CMP apparatus 1 includes a grinding endpoint detection device 10 for detecting the grinding endpoint of workpiece W during grinding. The grinding endpoint detection device 10 includes a measuring unit 20 for measuring the film thickness of workpiece W and a detection unit 30 for detecting the grinding endpoint of workpiece W.

[0030] The measuring unit 20 is a so-called optical interferometric film thickness sensor. The measuring unit 20 includes a light source 21, a sensing head 22, and a beam splitter 23.

[0031] The light source 21 is, for example, a halogen light source that emits white light with a wavelength of 400 to 800 nm, but is not limited to this. The measurement light emitted from the light source 21 is transmitted to the sensor head 22 via the first optical fiber 24, the fixed-side mirror tube 25, the rotating-side mirror tube 26, and the second optical fiber 27.

[0032] The first optical fiber 24 is a Y-shaped fiber that bundles multiple optical fibers and branches midway through its length. One end of the fiber is connected to the light source 21 and the beam splitter 23, and the other end is connected to the fixed-side mirror tube 25. The bundle diameter of the first optical fiber 24 is, for example, set to 100 μm. However, the structure of the first optical fiber 24 is not limited to this.

[0033] The fixed-side mirror tube 25 and the rotating-side mirror tube 26 are arranged opposite each other at a predetermined distance, and can illuminate and receive light from each other. That is, light is transmitted wirelessly between the fixed-side mirror tube 25 and the rotating-side mirror tube 26. Hereinafter, the optical path that transmits light wirelessly will be referred to as the "hollow optical path OP".

[0034] The optical axis of the fixed-side lens barrel 25 is configured to be approximately aligned with the optical axis of the first optical fiber 24. The fixed-side lens barrel 25 is supported by a support arm 28. The support arm 28 is mounted on a movable stage 29, and the fixed-side lens barrel 25 can move relative to the rotating-side lens barrel 26 by moving the movable stage 29 in the horizontal or vertical direction.

[0035] The rotating side mirror barrel 26 is mounted on the bottom of the rotating shaft portion 2a of the pressure plate 2 via an attachment 26a. The outer periphery of the rotating side mirror barrel 26 is supported by the attachment 26a. The attachment 26a is configured to be easily installed and removed from the rotating shaft portion 2a by fastening bolts into elongated holes or the like (not shown in the figure). In addition, the attachment 26a can be finely adjusted in the horizontal direction relative to the rotating shaft portion 2a.

[0036] The second optical fiber 27 is a type I optical fiber formed by bundling multiple optical fibers. One end of it is connected to the rotating side mirror tube 26, and the other end is connected to the sensing head 22. The bundle diameter of the second optical fiber 27 is set to, for example, 1000 μm. However, the structure of the second optical fiber 27 is not limited to this. The optical axis of the rotating side mirror tube 26 and the optical axis of the second optical fiber 27 are configured to be approximately aligned.

[0037] The sensor head 22 is housed within the observation hole 8 and is positioned opposite the observation window 9. The observation hole 8 is formed by penetrating the pressure plate 2 and the grinding pad 5 in the vertical direction. The observation hole 8 is offset radially by a predetermined distance from the rotation axis A of the pressure plate 2. The shape of the observation hole 8 is, for example, an elongated ellipse when viewed from above.

[0038] The observation window 9 is configured to close the upper end of the observation hole 8. The observation window 9 is integrated with the grinding pad 5 by bonding its peripheral surface to the grinding pad 5, etc., so that the slurry on the grinding pad 5 will not leak during grinding. The material of the observation window 9 can be any material, such as polyurethane, as long as it is optically transparent with respect to the wavelength of the measurement light described later.

[0039] The measurement light emitted from the light source 21 is transmitted to the sensor head 22 via the first optical fiber 24, the fixed-side mirror tube 25, the rotating-side mirror tube 26, and the second optical fiber 27. That is, the measurement light is transmitted through the hollow optical path OP.

[0040] Then, the measuring light illuminating the workpiece W from the sensor head 22 passes through the observation window 9 and reaches the workpiece W. At this time, since the sensor head 22 rotates integrally with the pressure plate 2, thus... Figure 3 As shown, when the workpiece W passes through the observation window 9, the sensor head 22 illuminates the workpiece W with measuring light at the film thickness measurement position MP, scanning within the workpiece W in a manner that passes through the rotation center of the workpiece W and traverses the workpiece W along the rotation direction D1 of the pressure plate 2. That is, multiple measurements can be performed in a very short time during one revolution of the pressure plate 2.

[0041] Furthermore, the sensor head 22 receives reflected light from the surface and back of the polished layer of the workpiece W, which is reflected and passes through the observation window 9. The reflected light received by the sensor head 22 is transmitted to the beam splitter 23 via the second optical fiber 27, the rotating side mirror tube 26, the fixed side mirror tube 25, and the first optical fiber 24. That is, the reflected light passes through the hollow optical path OP. In addition, the sensor head 22 is not limited to illuminating or receiving light perpendicularly to the observation window 9; the optical path may also be refracted by reflective components or the like.

[0042] The beam splitter 23 is connected to the fixed-side mirror tube 25 via the first optical fiber 24. The beam splitter 23 decomposes the reflected light from the workpiece W according to the wavelength, generating a beam split waveform that represents the relationship between the wavelength and the intensity of the reflected light. In addition, the beam splitter 23 uses Fourier analysis or other methods to calculate the film thickness of the workpiece W during grinding based on the beam split waveform.

[0043] The detection unit 30 compares the film thickness of the workpiece W being processed, as measured by the spectrophotometer 23, with a pre-stored set value for the film thickness corresponding to the grinding endpoint. When the measured film thickness of the workpiece W reaches the set value, the detection unit 30 detects the grinding endpoint of the workpiece W. Additionally, the detection unit 30 outputs a stop signal for the CMP device 1 to the controller 6, thus ending the grinding of the workpiece W.

[0044] Next, in order to enable the grinding endpoint detection device 10 to detect the grinding endpoint with high precision, the preferred structure of the fixed side mirror tube 25 and the rotating side mirror tube 26 will be described.

[0045] If the amount of reflected light acquired is unstable and fluctuates, the measurement accuracy of the measuring unit 20 will decrease. Therefore, it is preferable that the fluctuations in the amounts of the measuring light and reflected light are stable to a degree that does not affect the measurement accuracy. Regarding the main reasons that may cause significant fluctuations in the amount of light within the measuring unit 20, the following reasons are considered, for example.

[0046] (1) The circumferential vibration of the rotation axis A of the pressure plate 2 and the optical axis of the rotating side mirror tube 26;

[0047] (2) The distance of the hollow optical path OP;

[0048] (3) Coaxiality between the optical axis of the fixed side lens tube 25 and the optical axis of the rotating side lens tube 26;

[0049] (1) Circumferential vibration of the rotation axis A of the pressure plate 2 and the optical axis of the rotating side mirror tube 26

[0050] The less circumferential vibration occurs when the rotation axis A of the pressure plate 2 rotates relative to the optical axis of the rotating side mirror tube 26, the less variation there is in the amount of light acquired. Table 1 shows the deviation in the amount of light acquired and the deviation in the measured values ​​in the ratio of the circumferential vibration of the rotating side mirror tube 26 to the diameter of the second optical fiber 27 (circumferential vibration ratio). Furthermore, the "circumferential vibration ratio" in Table 1 refers to the percentage obtained by dividing the circumferential vibration of the rotating side mirror tube 26 (15 μm, 30 μm, and 50 μm) by the bundle diameter of the second optical fiber 27 (1000 μm).

[0051] Table 1

[0052]

[0053] • Oxide film thickness: 2 μm

[0054] As shown in Table 1, as the circumferential vibration ratio of the rotating side mirror tube 26 increases, the deviation in the measurement of light acquisition and film thickness also increases, and the measurement accuracy deteriorates.

[0055] Therefore, in this embodiment, in order to stably obtain the amount of light acquired, the vibration of the optical axis of the rotating side lens barrel 26 when rotating relative to the rotation axis A of the pressure plate 2 is set to 1.5 μm (circumferential vibration ratio: 1.5%). Furthermore, the assembly of the rotating side lens barrel 26 to the rotation axis 2a is performed, for example, by rotating the pressure plate 2 while using an electronic micrometer to confirm the circumferential vibration of the rotating side lens barrel 26, adjusting the mounting of the accessory 26a relative to the rotation axis 2a, so as to position the rotating side lens barrel 26 at a position where the circumferential vibration is below the specified value.

[0056] (2) When the distance between the hollow optical path OP (the gap between the fixed side tube 25 and the rotating side tube 26) is too wide, the light diverges, the light transmission rate decreases, the measurement accuracy deteriorates, and the diverged light reflected from the end face of the fixed side tube 25 or the end face of the rotating side tube 26 becomes noise.

[0057] On the other hand, if the distance of the hollow optical path OP is too close, there is a concern that the rotating side mirror tube 26 may come into contact with the fixed side mirror tube 25 and break when the pressure plate 2 rotates. Table 2 shows the relationship between the distance (gap width) of the hollow optical path OP and the deviation in the measured film thickness.

[0058] Table 2

[0059]

[0060] • Oxide film thickness: 2 μm

[0061] Table 2 shows that if the distance of the hollow optical path OP is 1.5 mm or more, the deviation in film thickness measurement worsens as the distance of the hollow optical path OP increases. On the other hand, if the distance of the hollow optical path OP is 1 mm or less, the deviation in film thickness measurement remains approximately constant.

[0062] Therefore, in this embodiment, in order to reduce the deviation in film thickness measurement and suppress light divergence, the distance of the hollow optical path OP is set to 0.5 mm. Furthermore, the adjustment of the distance of the hollow optical path OP is performed, for example, as follows: starting from the state where the fixed-side mirror tube 25 is in contact with the rotating-side mirror tube 26, the moving stage 29 is driven to move the fixed-side mirror tube 25 away from the rotating-side mirror tube 26; when the movement of the moving stage 29 reaches 0.5 mm, the moving stage 29 is stopped.

[0063] (3) Coaxiality between the optical axis of the fixed-side lens tube 25 and the optical axis of the rotating-side lens tube 26

[0064] The less vibration the optical axis of the fixed-side lens tube 25 relative to the optical axis of the rotating-side lens tube 26, the less variation in the amount of light acquired.

[0065] Therefore, in this embodiment, the relative position of the fixed-side lens barrel 25 with respect to the rotating-side lens barrel 26 is set such that the variation in the amount of light obtained is within ±5%. Furthermore, the horizontal positioning of the fixed-side lens barrel 25 is performed, for example, by rotating the pressure plate 2 while driving the movable stage 29 to move the fixed-side lens barrel 25 horizontally, and by confirming the variation in the amount of light obtained by the beam splitter 23 corresponding to the position of the fixed-side lens barrel 25.

[0066] In this way, the grinding endpoint detection device 10 of this embodiment measures the film thickness of the workpiece W being ground on the grinding pad 5 pressed on the pressure plate 2, and detects the grinding endpoint based on the film thickness of the workpiece W. The grinding endpoint detection device 10 has the following structure, which includes a fixed side mirror tube 25, a rotating side mirror tube 26, and a sensor head 22. The fixed side mirror tube 25 is disposed outside the pressure plate 2 and is connected to the light source 21 and the beam splitter 23 via the first optical fiber 24. The rotating side mirror tube 26 is disposed on the pressure plate 2 and transmits light wirelessly between itself and the fixed side mirror tube 25. The sensor head 22 is housed in the observation hole 8 formed in the pressure plate 2 and the grinding pad 5, and is connected to the rotating side mirror tube 26 via the second optical fiber 27. When the workpiece W passes through the observation hole 8, it irradiates the workpiece W with measuring light and receives the reflected light from the workpiece W.

[0067] With this structure, the sensor head 22 and the fixed side lens tube 25 can rotate together with the pressure plate 2. The film thickness measurement position MP is scanned by traversing the workpiece W every time the pressure plate 2 rotates. Therefore, film thickness measurement can be carried out with high precision over a wide range within the workpiece W in a short time.

[0068] Furthermore, when the light source 21 and the beam splitter 23 are mounted on the pressure plate 2, the light source 21 and the beam splitter 23 may be damaged due to the centrifugal force generated when the pressure plate 2 rotates, or the power supply to the light source 21 and the beam splitter 23 may become unstable or mixed with noise. However, by setting the light source 21 and the beam splitter 23 outside the pressure plate 2, the film thickness of the workpiece W can be measured stably.

[0069] Furthermore, the grinding endpoint detection device 10 of this embodiment has the following structure, in which the fixed side mirror tube 25 and the rotating side mirror tube 26 are arranged opposite each other with a gap.

[0070] With this structure, when the pressure plate 2 rotates at high speed, the situation where the fixed side mirror tube 25 comes into contact with the rotating side mirror tube 26 and breaks can be suppressed, so the film thickness of the workpiece W can be measured stably.

[0071] Furthermore, the grinding endpoint detection device 10 of this embodiment has the following structure, in which the rotating side mirror barrel 26 is provided on the rotating shaft portion 2a of the pressure plate 2 via an attachment 26a that can be freely attached to and detached from the pressure plate 2.

[0072] This structure allows for easy assembly of the rotating side mirror tube 26 onto the rotating shaft portion 2a.

[0073] Furthermore, the grinding endpoint detection device 10 of this embodiment has the following structure, which also includes a movable stage 29 that moves the fixed side mirror tube 25 relative to the rotating side mirror tube 26.

[0074] With this structure, by changing the relative position of the fixed-side mirror tube 25 to the rotating-side mirror tube 26, the gap between the fixed-side mirror tube 25 and the rotating-side mirror tube 26, and the coaxiality between the optical axis of the fixed-side mirror tube 25 and the optical axis of the rotating-side mirror tube 26 can be easily adjusted, thus enabling stable measurement of the film thickness of the workpiece W.

[0075] Furthermore, the CMP apparatus 1 in this embodiment has a structure that includes a grinding endpoint detection device 10.

[0076] With this structure, the sensor head 22 and the fixed side lens tube 25 can rotate together with the pressure plate 2. The film thickness measurement position MP is scanned by traversing the workpiece W every time the pressure plate 2 rotates. Therefore, film thickness measurement can be carried out with high precision over a wide range within the workpiece W in a short time.

[0077] Furthermore, various modifications can be made to the present invention in addition to those described above, provided that they do not depart from the spirit of the invention, and the present invention certainly relates to such modified solutions.

[0078] Explanation of the labels:

[0079] Label 1 indicates a CMP device;

[0080] The number 2 indicates a pressure plate;

[0081] The designation 2a indicates the rotating shaft (of the pressure plate);

[0082] The designation 3 indicates a grinding head;

[0083] The designation 3a indicates the rotating shaft (of the grinding head);

[0084] The number 4 indicates a motor;

[0085] The designation 5 indicates an abrasive pad;

[0086] The number 6 indicates the controller;

[0087] The number 7 indicates a chuck;

[0088] The designation 7a indicates the chuck worktable;

[0089] The designation 7b indicates the retaining face;

[0090] Number 8 indicates an observation well;

[0091] Number 9 indicates the observation window;

[0092] The designation 10 indicates a grinding endpoint detection device;

[0093] The designation 20 indicates the measuring section;

[0094] The number 21 indicates a light source;

[0095] The number 22 indicates the sensor head;

[0096] The designation 23 indicates a spectrophotometer;

[0097] The number 24 indicates the first optical fiber;

[0098] The designation 25 indicates the fixed-side end tube;

[0099] The number 26 indicates the rotating side tube;

[0100] 26a indicates an appendix;

[0101] The label 27 indicates the second optical fiber;

[0102] The number 28 indicates the support arm;

[0103] Number 29 indicates a mobile station;

[0104] The designation 30 indicates the testing department;

[0105] Symbol A represents the axis of rotation;

[0106] The symbol OP represents a hollow optical path;

[0107] The symbol W represents the workpiece.

Claims

1. A grinding endpoint detection device, wherein the grinding endpoint detection device measures the film thickness of a workpiece, the workpiece being pressed onto a grinding pad on a pressure plate for grinding, and the grinding endpoint is detected based on the film thickness of the workpiece, characterized in that, The grinding endpoint detection device includes: A fixed-side lens barrel is disposed outside the aforementioned pressure plate and is connected to the light source and the beam splitter via the first optical fiber. A rotating side mirror tube is disposed on the pressure plate and transmits light wirelessly between the rotating side mirror tube and the fixed side mirror tube in a non-mechanical connection manner. The sensor head is housed in an observation hole formed in the pressure plate and the polishing pad, and is connected to the rotating side mirror via a second optical fiber. When the workpiece passes through the observation hole, the sensor head illuminates the workpiece with measuring light and receives the reflected light from the workpiece.

2. The grinding endpoint detection device according to claim 1, characterized in that, The fixed-side mirror tube and the rotating-side mirror tube are arranged opposite each other with a gap between them.

3. The grinding endpoint detection device according to claim 1, characterized in that, The aforementioned rotating side mirror tube is mounted on the rotating shaft of the aforementioned pressure plate via an accessory, which can be adjusted to its horizontal position relative to the rotating shaft of the aforementioned pressure plate.

4. The grinding endpoint detection device according to claim 1, characterized in that, It also includes a movable stage that moves the fixed-side mirror tube relative to the rotating-side mirror tube.

5. A CMP apparatus, comprising the grinding endpoint detection device according to any one of claims 1 to 4.

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