An on-line polishing pad thickness and flatness measurement device and method

Abstract

This invention discloses an online measurement device and method for polishing pad thickness and flatness. The measurement device includes a laser rangefinder, n eddy current rangefinders, n measuring wafer units, and a feed unit. This invention uses the laser rangefinder to obtain the distance between the laser rangefinder probe and the upper and lower surfaces of the measuring wafer in real time. The distance between the laser rangefinder probe and the lower surface of the measuring wafer reflects the height of various points on the polishing pad surface, and the flatness of the polishing pad can be calculated. The difference between the distance between the laser rangefinder probe and the upper and lower surfaces of the measuring wafer is the measuring wafer thickness. This invention uses an indirect measurement method, eliminating the influence of measurement on the polishing process, avoiding probe wear, and the measurement process is not affected by the polishing fluid. It overcomes the problem of low measurement accuracy caused by the porous material and slotted design of the polishing pad. This invention uses standard optical flat calibration to compensate for motion errors and assembly errors. The measuring wafer unit uses a weight loading method, which is simple, reliable, and has high loading accuracy.

Description

Technical Field

[0001] This invention belongs to the field of precision wafer processing, and specifically relates to an online measurement device and method for polishing pad thickness and flatness. Background Technology

[0002] Currently, wafer processing generally involves processes such as ingot grinding, slicing, chamfering, surface grinding, and polishing. Polishing, as the final step in precision wafer machining, requires ensuring high surface accuracy. During polishing, the polishing pad adheres to the surface of the polishing disc and rotates with it. Under polishing pressure, the wafer and polishing pad come into close contact, while polishing fluid drips onto the surface of the polishing pad. To allow the polishing fluid to better penetrate the interface between the wafer and the polishing pad, the polishing pad has a microporous structure with grooves on its surface.

[0003] Polishing pads are one of the important factors affecting the geometric accuracy of wafers. Polishing pads are often made of materials with low hardness, such as polyurethane. Therefore, the surface of the polishing pad is prone to wear during processing. When the flatness error and thickness loss of the polishing pad reach a certain level, it will lead to serious deterioration of the wafer surface. Therefore, it is necessary to measure the thickness and flatness of the polishing pad online so that operators can repair or replace the polishing pad in time to improve the wafer yield.

[0004] Chinese patent CN202010822565.3 describes a method for obtaining the surface shape of a polishing pad by measuring the height of various points on the polishing pad through the swing of a displacement sensor. However, because it does not consider the polishing environment, it cannot achieve online measurement of the flatness of the polishing pad. In addition, this patent cannot achieve online measurement of the thickness of the polishing pad.

[0005] Chinese patent CN201910028544.1 describes a dressing device and polishing equipment for measuring the thickness of polishing pads. The device uses a contact displacement sensor that is always pressed against the top surface of the dressing mechanism to measure the displacement of the dressing mechanism and thus obtain the change in the thickness of the polishing pad. However, in actual processing, the change in the thickness of the polishing pad is generally only a few tens of micrometers. This patent does not take into account the wear and tear of the dressing mechanism when dressing the polishing pad, resulting in insufficient measurement accuracy.

[0006] Chinese patent CN201780057451.0 describes a method for detecting the thickness of a polishing pad used in chemical mechanical polishing. However, this patent does not consider the wear and tear of the conductor during the polishing process, resulting in low measurement accuracy. When the conductor is worn, new impurities are introduced during the polishing process, which will affect the surface quality of the polished workpiece. The recesses machined on the lower surface of the polishing pad to place the sensor will cause insufficient rigidity of the polishing pad at that location. During the polishing process, this location is prone to deformation under the action of force and heat, which will affect the geometric accuracy of the polished workpiece. Summary of the Invention

[0007] To address the aforementioned problems in existing technologies, this invention designs an online measurement device and method for polishing pad thickness and flatness. Without affecting workpiece polishing, this method adapts to the wafer polishing environment, avoids sensor probe wear, and enables online measurement of polishing pad thickness and flatness. This allows for timely acquisition of polishing pad wear and surface shape changes, reducing wafer flatness errors and improving wafer polishing yield and processing efficiency.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: an online measuring device for the thickness and flatness of a polishing pad, wherein the polishing pad is bonded to a polishing disc and the workpiece is in close contact with the surface of the polishing pad;

[0009] The measuring device includes a laser rangefinder, n eddy current rangefinders, n measuring wafer units, a feed unit, and a measuring support.

[0010] The measuring support includes a beam frame, support columns, and a magnetic base. There are two support columns, which are respectively fixed on the magnetic base and installed at both ends of the beam frame. The magnetic base is placed on a polishing machine table. The polishing machine table is made of iron.

[0011] The n measuring wafer units are fixed side by side, at equal intervals and heights, on the side of the beam frame; the distance between the central axes of two adjacent measuring wafer units is a;

[0012] The feeding unit includes a lead screw, guide rails, a motor, and a guide rail slide. Two guide rails are horizontally parallel and fixedly mounted on the beam frame. The lead screw is mounted on the beam frame between the two guide rails and is connected to the guide rail slide via a threaded connection. The guide rail slide is slidably connected to the guide rails. One end of the lead screw is fixedly connected to the output shaft of the motor, which is fixedly mounted on the beam frame. The laser rangefinder is vertically mounted on the guide rail slide. The motor drives the lead screw to rotate, thus achieving horizontal movement of the guide rail slide.

[0013] The measuring wafer unit includes a measuring wafer, a guide post, screw B, a washer, a weight, an adapter, a loading shaft, an air-bearing bushing, a support base, screw C, and a clamp. The clamp is fixed to the lower end face of the loading shaft by screw C. The guide post is fixed to the center of the loading shaft by the adapter. The adapter is fixed to the upper end face of the loading shaft by screw B and a washer. The support base is fixed to the beam frame by screw A. The air-bearing bushing is installed inside the support base, and the loading shaft is nested inside the air-bearing bushing. During operation, clean air at 0.2–0.6 MPa is introduced into the gap between the air-bearing bushing and the loading shaft. Under the action of air film pressure, the loading shaft is stabilized at the center of the air-bearing bushing. The weight is nested on the guide post. The guide post and the loading shaft are coaxial. The centers of the guide post, the loading shaft, and the clamp are all through holes. The eddy current ranging sensor is embedded in the clamp, and the lower surface of the eddy current ranging sensor is in close contact with the upper surface of the measuring wafer.

[0014] Furthermore, the measuring wafer is made of the same material as the workpiece, which is a transparent material.

[0015] Furthermore, the laser emitted by the laser ranging sensor head passes through the guide post, the loading shaft, and the through hole in the center of the fixture.

[0016] Furthermore, the measurement wafer units are evenly distributed on the beam frame, and the number n is greater than 3, with n being an odd number.

[0017] Furthermore, the distance 'a' between the central axes of two adjacent measuring wafer units is between (0.1 and 0.3)D, where D is the diameter of the polishing disk.

[0018] A method for online measurement of polishing pad thickness and flatness, utilizing an online polishing pad thickness and flatness measurement device, includes the following steps:

[0019] A. Calibration

[0020] The measuring device is mounted on the upper surface of the polishing machine table using the magnetic attraction of the magnetic base. The beam of the measuring device spans the polishing pad, and a standard optical flat is placed on the upper surface of the polishing pad. The drive feed unit moves the laser rangefinder sensor from the first measuring wafer unit to each measuring wafer unit, recording the distance between the laser rangefinder sensor probe and the standard optical flat at each measuring wafer unit position, denoted as k1, k2…k n ;

[0021] B. Online Measurement

[0022] During workpiece polishing, the drive feed unit moves the laser rangefinder sensor, starting from the first measuring wafer unit, sequentially above each measuring wafer unit, measuring the distance from the laser rangefinder sensor probe to the upper surface of the measuring wafer, denoted as q1, q2…q. n Simultaneously, the distance between the laser rangefinder sensor and the lower surface of the measuring chip is measured and denoted as p1, p2…p n Record the readings of the eddy current ranging sensor, denoted as h1, h2…h n ;

[0023] C. Calculate flatness and thickness

[0024] Based on the measurement results of steps AB, calculate the flatness and thickness of the polishing pad. The formula for calculating the flatness ΔZ is as follows:

[0025] ΔZ=max[(p i -k i )-(p j -k j )], i∈[1,n], j∈[1,n],

[0026] Thickness ΔF at each measurement point i The calculation formula is as follows:

[0027] ΔF i =h i -(p i -q i ), i∈[1,n].

[0028] Compared with existing inventions, the present invention has the following beneficial effects:

[0029] 1. This invention enables high-precision online measurement of both polishing pad thickness and flatness simultaneously. Employing an indirect measurement method, it is unaffected by polishing fluid interference and overcomes the low accuracy issues caused by the porous material and slotted design of the polishing pad. A laser rangefinder sensor provides real-time data on the distances between its probe and the upper and lower surfaces of the measuring wafer. The distance between the laser rangefinder probe and the lower surface of the measuring wafer reflects the height of various points on the polishing pad surface, allowing calculation of the polishing pad's flatness. The difference between the distances between the laser rangefinder probe and the upper and lower surfaces of the measuring wafer represents the wafer thickness, which continuously decreases during polishing. An eddy current rangefinder sensor probe is embedded in the fixture, maintaining constant contact with the upper surface of the measuring wafer. It provides real-time data on the distance between the upper surface of the measuring wafer and the polishing pad. The difference between this distance and the wafer thickness is the polishing pad thickness. Since the measuring wafer and the workpiece are made of the same material, no new impurities are introduced during the measurement process.

[0030] 2. This invention ensures a safe measurement environment for the sensor by using a measurement chip to prevent the eddy current sensor and laser rangefinder from being directly exposed to the polishing environment. Since the equipment itself is constantly in motion during actual workpiece polishing, and the polishing slurry splashes, containing a large number of abrasive particles and oxidants, this invention avoids wear and tear on the measurement probe.

[0031] 3. This invention uses standard optical flat calibration to compensate for the straightness error of the feed unit, the installation error of the measuring bracket, and the horizontal error of the polishing machine table. This ensures the accuracy of online measurement of polishing pad thickness and flatness. Furthermore, the measuring device can be used simply by mounting it on the polishing machine table via a magnetic base. It is easy to install and remove, has high measurement accuracy, and can also measure polishing pads of multiple specifications with one measuring device, thus reducing measurement costs.

[0032] 4. The measurement wafer unit in this invention adopts a weight loading method, which is simple and reliable in structure and has high loading accuracy. During measurement, weights of different masses are placed on the guide post on the loading shaft according to the different hardness of the polishing pad. Generally speaking, when the polishing pad is soft, a smaller weight should be used to avoid large deformation of the polishing pad, which would increase the measurement error. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the measuring device of the present invention.

[0034] Figure 2 This is a cross-sectional view of the measurement wafer unit of the present invention.

[0035] Figure 3 This is a schematic diagram illustrating the measurement principle of the present invention at the initial stage of processing.

[0036] Figure 4 This is a schematic diagram illustrating the measurement principle of the present invention during the processing.

[0037] In the diagram: 1-polishing disc, 2-polishing machine base, 3-polishing pad, 4-measuring wafer, 5-guide rail slide, 6-laser rangefinder sensor, 7-lead screw, 8-guide rail, 9-screw A, 10-motor, 11-beam frame, 12-support column, 13-magnetic seat, 14-workpiece, 15-eddy current rangefinder sensor, 101-guide column, 102-screw B, 103-washer, 104-weight, 105-adapter, 106-loading shaft, 107-air bearing bush, 108-support seat, 109-screw C, 110-clamp. Detailed Implementation

[0038] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0039] This invention addresses the problems of existing methods for measuring the thickness and flatness of polishing pads, such as significant interference from polishing fluid, low measurement accuracy due to the porous material and grooved design of polishing pads, easy introduction of impurities during the measurement process, easy wear of the measuring probe, and difficulty in achieving online measurement. It provides an online measurement device and method for the thickness and flatness of polishing pads, comprising:

[0040] An online measuring device for the thickness and flatness of a polishing pad, wherein the polishing pad 3 is bonded to a polishing disc 1 and the workpiece 14 is in close contact with the surface of the polishing pad 3;

[0041] The measuring device includes a laser rangefinder 6, five eddy current rangefinders 15, five measuring wafer units, a feeding unit, and a measuring support.

[0042] The measuring support includes a beam frame 11, support columns 12, and magnetic bases 13. There are two support columns 12, which are respectively fixed on the magnetic bases 13 and installed at both ends of the beam frame 11. The magnetic bases 13 are placed on the polishing machine table 2. The polishing machine table 2 is an iron machine table.

[0043] The five measuring chip units are fixed side by side, at equal intervals and heights, on the side of the beam frame 11;

[0044] The feeding unit includes a lead screw 7, guide rails 8, a motor 10, and a guide rail slide 5. Two guide rails 8 are horizontally parallel and fixedly mounted on the beam frame 11. The lead screw 7 is mounted on the beam frame 11 between the two guide rails 8 and is connected to the guide rail slide 5 via a threaded connection. The guide rail slide 5 is slidably connected to the guide rails 8. One end of the lead screw 7 is fixedly connected to the output shaft of the motor 10, which is fixedly mounted on the beam frame 11. The laser rangefinder 6 is vertically mounted on the guide rail slide 5. The motor 10 drives the lead screw 7 to rotate, thereby enabling the guide rail slide 5 to move horizontally.

[0045] The measuring wafer unit includes a measuring wafer 4, a guide post 101, a screw B102, a washer 103, a weight 104, an adapter 105, a loading shaft 106, an air-bearing bushing 107, a support base 108, a screw C109, and a clamp 110. The clamp 110 is fixed to the lower end face of the loading shaft 106 by the screw C109. The guide post 101 is fixed to the center of the loading shaft 106 by the adapter 105. The adapter 105 is fixed to the upper end face of the loading shaft 106 by the screw B102 and the washer 103. The support base 108 is fixed to the beam frame 11 by the screw A9. The air-bearing bushing 107 is installed inside the support base 108, and the loading shaft 106 is nested inside the air-bearing bushing 107. During operation, the air-bearing bushing 107 and the loading shaft 106... Clean air at 0.2–0.6 MPa is introduced into the gap between the two parts. Under the action of air film pressure, the loading shaft 106 is stabilized at the center of the air-bearing sleeve 107. The weight 104 is nested on the guide post 101. The guide post 101 and the loading shaft 106 are coaxial. Under the action of the weight, the measuring wafer can always be in close contact with the upper surface of the polishing pad. The pressure on the surface of the measuring wafer is in the range of 10–20 kPa. The center of the guide post 101, the loading shaft 106 and the clamp 110 are all through holes. The eddy current ranging sensor 15 is embedded in the clamp 110. The lower surface of the eddy current ranging sensor 15 is in close contact with the upper surface of the measuring wafer 4. The eddy current sensor 15 has a measurement accuracy of 0.1 μm and can obtain the distance between the upper surface of the measuring wafer 4 and the upper surface of the polishing pad 1 in real time.

[0046] Furthermore, the measuring wafer 4 and the workpiece 14 are made of the same material, which is transparent material. During polishing, the upper and lower surfaces of the measuring wafer 4 can efficiently reflect light.

[0047] Furthermore, the laser emitted by the laser rangefinder sensor 6 probe passes through the guide post 101, the loading shaft 106, and the through hole in the center of the fixture 110. The laser sensor 6 has a measurement accuracy of 50nm, and the laser rangefinder sensor 6 can simultaneously obtain the distance between the upper and lower surfaces of the measuring wafer 4 and the probe.

[0048] Furthermore, there are a total of 5 measurement wafer units evenly distributed on the beam frame 11.

[0049] Furthermore, the distance a between the central axes of two adjacent measuring wafer units is 0.2D, where D is the diameter of the polishing disk 1, and the central axis of the intermediate measuring wafer unit coincides with the central axis of the polishing disk 1;

[0050] A method for online measurement of polishing pad thickness and flatness, utilizing an online polishing pad thickness and flatness measurement device, includes the following steps:

[0051] A. Calibration

[0052] Due to the high accuracy requirements, compensation is needed for the motion and assembly errors of the device. The optical flat surface has extremely high consistency, so a measuring device can be used to scan the surface of the optical flat. The changes in the measurement results can reflect the assembly and motion errors of the measuring device. The measuring device is installed on the upper surface of the polishing table 2 by the magnetic attraction of the magnetic seat 13. The beam 11 of the measuring device spans the polishing pad 3, and a standard optical flat is placed on the upper surface of the polishing pad 3. The drive feed unit drives the laser range sensor 6 to start recording from the first measuring wafer unit, and moves to each measuring wafer unit in sequence. The distance between the probe of the laser range sensor 6 and the standard optical flat at each measuring wafer unit position is recorded as k1, k2...k5.

[0053] B. Online Measurement

[0054] When polishing workpiece 14, the drive feed unit drives the laser range sensor 6 to start recording from the first measuring wafer unit and move sequentially above each measuring wafer unit. The distance between the probe of the laser range sensor 6 and the upper surface of the measuring wafer 4 is measured and recorded as q1, q2...q5. At the same time, the distance between the laser range sensor 6 and the lower surface of the measuring wafer 4 is measured and recorded as p1, p2...p5. The reading of the eddy current range sensor 15 is recorded and recorded as h1, h2...h5.

[0055] C. Calculate flatness and thickness

[0056] like Figure 3-4 As shown, during the actual processing, the thickness of the wafer 4 is reduced, and the surface of the polishing pad 3 experiences wear. The grooves of the polishing pad 3 also experience wear due to the impact of the polishing fluid. The relative heights of the polishing pad at the five measurement points are q1-k1, q2-k2…q5-k5. The flatness can be represented by the height range of the polishing pad at the five measurement points. The thicknesses of the five measured wafers are p1-q1, p2-q2…p5-q5. The thickness of the polishing pad at each measurement point can be represented by the difference between the eddy current sensor reading and the measured wafer thickness. The formulas for calculating flatness and thickness are as follows:

[0057] ΔZ=max[(p i -ki )-(p j -k j )], i∈[1,5], j∈[1,5],

[0058] Thickness ΔF at each measurement point i The calculation formula is as follows:

[0059] ΔF i =h i -(p i -q i ), i∈[1,5).

[0060] This invention is not limited to this embodiment. Any equivalent concept or modification within the technical scope disclosed in this invention shall be included within the protection scope of this invention.

Claims

1. An online measuring device for the thickness and flatness of a polishing pad, wherein a polishing pad (3) is bonded to a polishing disc (1) and a workpiece (14) is in close contact with the surface of the polishing pad (3); Its features are: The measuring device includes a laser rangefinder sensor (6). n One eddy current ranging sensor (15) n One measurement wafer unit, one feed unit, and one measurement bracket; The measuring support includes a beam frame (11), support columns (12) and a magnetic seat (13). There are two support columns (12), which are fixed on the magnetic seat (13) and installed at both ends of the beam frame (11). The magnetic seat (13) is placed on a polishing machine table (2). The polishing machine table (2) is an iron machine table. The n The measurement wafer units are fixed side by side, at equal intervals and heights, on the side of the beam frame (11); the distance between the central axes of two adjacent measurement wafer units is a ; The feeding unit includes a lead screw (7), a guide rail (8), a motor (10), and a guide rail slide (5). There are two guide rails (8), which are fixedly installed on the beam frame (11) in parallel horizontal direction. The lead screw (7) is installed on the beam frame (11) between the two guide rails (8). The lead screw (7) is connected to the guide rail slide (5) by a threaded connection. The guide rail slide (5) is slidably connected to the guide rail (8). One end of the lead screw (7) is fixedly connected to the output shaft of the motor (10). The motor (10) is fixedly installed on the beam frame (11). The laser rangefinder (6) is vertically installed on the guide rail slide (5). The motor (10) drives the lead screw (7) to rotate, thereby realizing the horizontal movement of the guide rail slide (5). The measuring wafer unit includes a measuring wafer (4), a guide post (101), a screw B (102), a washer (103), a weight (104), an adapter (105), a loading shaft (106), an air-bearing bushing (107), a support base (108), a screw C (109), and a clamp (110). The clamp (110) is fixed to the lower end face of the loading shaft (106) by the screw C (109), and the guide post (101) is fixed to the loading shaft by the adapter (105). At the center of (106), the adapter (105) is fixed to the upper end face of the loading shaft (106) by screw B (102) and washer (103), and the support base (108) is fixed to the beam frame (11) by screw A (9); the air bearing bush (107) is installed in the support base (108), and the loading shaft (106) is nested in the air bearing bush (107); during operation, 0.2~0.6 mm of fluid is introduced into the gap between the air bearing bush (107) and the loading shaft (106). Under the action of air film pressure, the loading shaft (106) is stabilized at the center of the air-floating bushing (107) with clean air of MPa. The weight (104) is nested on the guide post (101). The guide post (101) and the loading shaft (106) are coaxial. The center of the guide post (101), the loading shaft (106) and the fixture (110) are all through holes. The eddy current ranging sensor (15) is embedded in the fixture (110). The lower surface of the eddy current ranging sensor (15) is in close contact with the upper surface of the measuring crystal (4). The laser emitted by the laser rangefinder (6) probe passes through the guide post (101), the loading shaft (106), and the through hole in the center of the fixture (110) to simultaneously measure the distance between the laser rangefinder (6) probe and the upper surface of the measuring wafer (4) and the lower surface of the measuring wafer (4).

2. The online measuring device for polishing pad thickness and flatness according to claim 1, characterized in that: The measuring wafer (4) and the workpiece (14) are made of the same material, both being transparent.

3. The online measuring device for polishing pad thickness and flatness according to claim 1, characterized in that: The measuring wafer units are evenly distributed on the beam frame (11), and the number is... n Greater than 3 n Take an odd number.

4. The online measuring device for polishing pad thickness and flatness according to claim 1, characterized in that: The distance between the central axes of two adjacent measuring wafer units a In (0.1~0.3) D between, D The diameter of the polishing disc (1) is given.

5. A method for online measurement of polishing pad thickness and flatness, characterized in that: The measurement using the online measuring device for polishing pad thickness and flatness as described in claim 1 includes the following steps: A. Calibration The measuring device is mounted on the upper surface of the polishing table (2) by the magnetic attraction of the magnetic base (13). The beam frame (11) of the measuring device spans the polishing pad (3), and a standard optical flat is placed on the upper surface of the polishing pad (3). The drive feed unit drives the laser range sensor (6) to start recording from the first measuring wafer unit, and moves sequentially above each measuring wafer unit, recording the distance between the probe of the laser range sensor (6) and the standard optical flat at each measuring wafer unit position, denoted as . k 1, k 2… k n ; B. Online Measurement When polishing the workpiece (14), the drive feed unit moves the laser rangefinder (6) from the first measuring wafer unit to each measuring wafer unit, measuring the distance between the laser rangefinder (6) probe and the upper surface of the measuring wafer (4), and recording it as . q 1, q 2… q n Simultaneously, the distance between the laser rangefinder (6) and the lower surface of the measuring chip (4) is measured and recorded as... p 1, p 2… p n Record the reading of the eddy current ranging sensor (15) as . h 1, h 2… h n ; C. Calculate flatness and thickness Based on the measurement results of steps AB, calculate the flatness and thickness of the polishing pad (3). The formula for calculating Z is as follows: Z =max[( p i - k i )-( p j - k j )], i ∈[1, n ], j ∈[1, n ], Thickness at each measurement point F i The calculation formula is as follows: F i = h i -( p i - q i )， i ∈[1, n ]。

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