Method for Measuring Platen Torque in Double-Sided Polishing and Double-Sided Polishing Machine Using the Same

Abstract

To provide a method for measuring surface plate torque useful for control of polishing conditions and quality control in double-sided polishing, and a double-sided polishing machine using the same.SOLUTION: A method is used to measure torque acting on a surface plate in a double-sided polishing method for simultaneously polishing top and bottom surfaces of a workpiece by using the pair of surface plates arranged in the state of facing each other in upper and lower positions. Members 11a and 11b to be restrained are provided on the side of the surface plate. Support members 16a and 16b are provided outside the surface plate. Sensors 17a, 17b, 18a and 18b for measuring a contact force between the member to be restrained and the support member are provided.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a torque measurement method for a surface plate useful for managing the polishing surface quality of a workpiece, controlling polishing conditions, etc. in a double-sided polishing method for simultaneously polishing the upper and lower surfaces of a workpiece, and a double-sided polishing machine using the same.

Background Art

[0002] Double-sided polishing is employed in various fields because it can reduce the surface roughness of the surface of a workpiece, improve flatness, and easily obtain parallelism between the upper and lower processed surfaces. For example, semiconductor wafers, semiconductor devices, crystal oscillators, optical components such as photomasks, and the like. In particular, in recent years, the needs in the fields of difficult-to-machine materials and hard and brittle materials such as SiC and GaN, which are referred to as wide-bandgap semiconductors, have been increasing.

[0003] As a conventional double-sided polishing machine (device), for example, Patent Document 1 discloses a control system based on the work amount of the upper surface and the work amount of the lower surface of a workpiece, and calculates the surface plate torque required for calculating the work amount based on the current value of the drive motor. In this case, in a double-sided polishing machine composed of an upper surface plate and a lower surface plate, it is relatively easy to measure the torque acting on the upper surface plate. However, for the lower surface plate, various mechanical elements such as belts, gears, and bearings are added to the transmission of the driving force from the drive motor to the lower surface plate, and these become error factors, and measurement based on the current value of the drive motor or the like cannot be said to be accurate.

[0004] Further, Patent Document 2 discloses that a wafer holding plate for holding a semiconductor wafer is supported so as to be swingable with respect to a rotation axis, and a torque transmission pin is provided on this rotation axis. On the other hand, a mechanism in which the wafer holding plate rotates by engaging a torque drive pin provided on the wafer holding plate side with the torque transmission pin is disclosed, and it is described that a strain detection gauge is attached to this torque drive pin to indirectly monitor a change in frictional force. However, the above technology is for transmitting a rotational force to the surface plate and cannot be applied to a double-sided polishing machine.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide a method for measuring a platen torque useful for controlling polishing conditions and quality control in double-sided polishing, and a double-sided polishing machine using the same.

Means for Solving the Problems

[0007] The method for measuring the platen torque in double-sided polishing according to the present invention is a method for measuring the torque acting on the platen in a double-sided polishing method in which the upper and lower surfaces of a workpiece are simultaneously polished using a pair of platens arranged opposite to each other vertically, characterized in that a constrained member is provided on the platen side, a support member is provided outside the platen, and a sensor for measuring the contact force between the constrained member and the support member is provided.

[0008] Here, the relationship between the constrained member provided on the platen side and the support member provided outside the platen means a relationship in which the support member restricts the platen from rotating due to the frictional force generated by the contact force between the platen and the workpiece during polishing of the surface of the workpiece. Therefore, the constrained member provided on the platen side may be a pin-shaped or stepped convex portion, and the support member provided outside the platen is not limited in its shape as long as it contacts the constrained member and can restrict the rotating movement of the platen, such as an arm shape or a bar shape.

[0009] The sensor used in the present invention is for detecting the contact force between the constrained member on the platen side and the support member outside the platen and measuring the platen torque acting on the platen. Examples include strain gauges and piezo elements. A strain gauge detects strain caused by a contact force, and is formed, for example, in a fine linear shape on the surface of a substrate using a resistance foil with a thickness of several μm such as a Cu-Ni alloy. A strain gauge utilizes the property that the resistance of a metal resistor changes depending on its length and cross-sectional area, and is based on the proportional relationship between the amount of strain and the rate of change of resistance. On the other hand, a piezo element detects electric charges generated by receiving a force such as a contact force.

[0010] Double-sided polishing can polish the upper and lower surfaces of a workpiece simultaneously and has excellent parallelism between the upper and lower surfaces. For example, it is preferable that the upper surface plate on the upper side is suspended and held by a plurality of wires and rotates and slides in parallel with respect to the lower surface plate on the lower side. Also, the loss power on the lower surface plate side required to measure the lower surface plate torque by the following formula (1) from the power consumption of the drive motor on the lower surface plate side can be obtained based on the surface plate torque of the upper surface plate in a co-polishing state where no workpiece is interposed between the upper surface plate and the lower surface plate. TIFF0007697663000001.tif13166 Here, P is the power consumption of the drive motor on the lower surface plate side, P loss is the loss power due to a transmission mechanism such as a gear on the lower surface plate side, and κ is a constant. The constant κ and P loss can be obtained in advance, and the details will be described later.

[0011] In the above formula (1), in the state where the upper surface plate and the lower surface plate are co-polished, since the torques acting on the upper surface plate and the lower surface plate are balanced, the lower surface plate torque T L is estimated from the power consumption and loss power of the drive motor on the lower surface plate side. Although the details will be described later, this is applicable not only to the type (3way) in which the upper surface plate is fixed and the lower surface plate side rotates, but also to the type (4way) in which both the upper surface plate and the lower surface plate rotate relative to each other. As a driving method for rotating the upper platen side, there are methods such as directly driving the upper platen with a motor and a method of branching the output shaft from a motor on the lower platen side. In any case, the platen torque on the upper platen side is relatively easy to measure, while the lower platen side often has complex transmission mechanisms such as a rotation mechanism and a revolution mechanism of the workpiece, and much of the output torque of the motor is lost in the above transmission mechanism. Therefore, if the torque loss on the lower platen side can be calculated in the state of co-grinding, the lower platen torque during polishing can be calculated based on it. For example, it can be obtained by the following formula (1-1). TIFF0007697663000002.tif13166 Here, T L1 is the lower platen torque, T ML is the driving motor torque on the lower platen side, κ1 is a constant, T loss is the loss torque on the lower platen side.

[0012] The double-sided polishing machine according to the present invention adopting the method for measuring the platen torque includes an upper platen suspended and held by a plurality of wires and a lower platen rotatably holding a workpiece to be polished, wherein the upper platen side has a restrained member, outside the platen has a support member, and is characterized by having a measuring means for the contact force between the restrained member and the support member.

Effect of the Invention

[0013] In the method for measuring the platen torque in double-sided polishing according to the present invention, since the force in the rotational direction generated on the platen by the frictional force with the surface of the workpiece is measured by the actual contact force generated between the restrained member provided on the platen side and the support member that restricts its movement, the measurement accuracy is higher than the method of indirectly obtaining only from the changes in the power and current on the conventional driving motor side.

Brief Description of the Drawings

[0014]

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Embodiments for Carrying Out the Invention

[0015] The method for measuring the platen torque in the double-sided polishing process according to the present invention will be described based on the following figures. First, the double-sided polishing machine used in the experiment is shown in Fig. 2. This double-sided polishing machine is an example manufactured by Hamai Sangyo Co., Ltd. of 3BN-3M10L. The upper platen 11 has a structure suspended by a wire 14, has a workpiece W to be polished between the upper platen and the lower platen 12, and the pressure applied to the workpiece during polishing is adjusted by an air cylinder 15. In this embodiment, a disk-shaped plate body 13 is connected to the tip of the piston rod 15a of the air cylinder 15, and the upper platen 11 is suspended by a wire 14 therefrom. It is empirically known that by suspending with a wire and sliding the upper platen parallel to the lower platen, there is an effect of enhancing the followability to the workpiece. In the setting where a pressure exceeding the self-weight of the upper platen is applied, the wire is in a state of being pressed by the deflection air cylinder. Also, the load applied to the platen is continuously controlled by an electro-pneumatic regulator for the air pressure of the air cylinder. Fig. 3 schematically shows the polishing mechanism. The polishing tool is a polishing pad attached to the upper and lower platens or the platen with a hollow structure. Since the workpiece W is structured to be inserted into a hole slightly larger than the workpiece provided on the carrier 12c, the workpiece rotates freely within the carrier. It is clamped between the upper and lower polishing tools for polishing. As shown in Fig. 3, the carrier revolves by the sun gear 12a and rotates by itself by the internal gear 12b in a planetary motion. For the drive method of the double-sided polishing machine, there are a 2-way method in which the carrier is rotated and revolved by the sun gear and the internal gear, and the upper and lower platens are not driven, a 3-way method in which the lower platen, the sun gear, and the internal gear are driven and the upper platen is not driven, and a 4-way method in which the upper platen, the lower platen, the sun gear, and the internal gear are all driven. Among these, in the 3-way double-sided polishing machine shown in the schematic diagram, the upper platen tries to rotate due to the frictional force with the workpiece.

[0016] Next, Fig. 1 shows an example of the measurement structure of the platen torque when using the 3-way method of Fig. 3. In Fig. 1, on the upper platen side, two first stopper pins 11a and second stopper pins 11b are provided at positions with radii r H1 , r H2 . The stopper pins are respectively in contact with two first holders 16a and second holders 16b as support members provided on the polishing machine main body side outside the upper platen. Forces F P1 , F P2 act on the upper platen whose rotational force is restricted, and strain gauges (17a, 17b, 18a, 18b) are respectively attached to both sides of the support member to measure the torque. Install a bridge box, an amplifier, and a measuring instrument for connecting the strain gauge to the non-rotating part of the polishing machine to achieve relatively easy real-time torque monitoring. The output from the strain gauge (KFGS-6-120-C1-16 L3M2R: manufactured by Kyowa Electronic Instruments Co., Ltd.) was amplified and controlled by a strain measurement unit (EDX-11A: manufactured by Kyowa Electronic Instruments Co., Ltd.) and a control unit (EDX-10B: manufactured by Kyowa Electronic Instruments Co., Ltd.) via a bridge box (DBV-120A-4: manufactured by Kyowa Electronic Instruments Co., Ltd.), and recorded on a notebook PC. The strain gauge was attached to the side surface of the support member using a cyanoacrylate-based instant adhesive (CC-33A: manufactured by Kyowa Electronic Instruments Co., Ltd.) and protected with ScotchVM Tape (manufactured by 3M) to prevent dirt and wire breakage. In this example, the two-active-gauge method was used. Specifically, strain gauges were attached to both sides of the support member (the first and second holders). Since compressive stress is generated on one side and tensile stress on the other side, it is possible to cancel out the tensile and compressive changes in the strain direction and detect only the bending strain.

[0017] The experimental method and experimental results will be described. Fig. 4 shows the experimental conditions. The polishing tool is a semi-fixed abrasive pad called Trizact Diamond Tile (TDT), which is adhered to the upper and lower platens. TDT has a structure in which diamond abrasive grains are embedded in resin. Different from the method of supplying an abrasive liquid containing abrasive grains, it prevents the deviation of the abrasive grain distribution from affecting the torque and enables evaluation regardless of the supply state of the abrasive liquid. 725N manufactured by DAIICHI CHEMICAL CO., LTD. was used as the coolant. In this experiment, four carriers were installed, and each carrier held one workpiece. The diameter of the workpiece is 25 mm, the thickness is 1 mm, and the material is borosilicate glass. The revolution radius of the carrier is 248 mm, and the center position of the wafer holding hole is offset 15 mm from the center of the carrier. The rotation speed of the lower platen is 12 min-1 , the revolution of the carrier is 6 minutes -1 , and the ratio of the self-rotation number is 1.4. Experiments were conducted by changing the load weights applied to the surface plate in the order of 20 N, 40 N, 60 N, 40 N, and 20 N. Note that when converted to the polishing pressure applied to the workpiece at that time, they are 9 kPa, 18 kPa, 27 kPa, 18 kPa, and 9 kPa, respectively. Fig. 5 shows the torque waveform measured when polishing is performed for 2 minutes under the condition of a load weight of 60 N. The measured torque waveform rises sharply due to the impact force at the moment when the support member (rotation stopper) contacts the stopper pin immediately after the start of rotation, and then periodic fluctuations with a period of 23.4 seconds are observed in the constant-speed range. After the rotation stops, it remains stationary at a constant value, but becomes zero by eliminating the contact between the rotation stopper and the stopper pin immediately after the rotation stops. In double-sided polishing, the wafer center position is offset from the center position of the carrier, so the distance between the surface plate center and the wafer center changes due to the planetary motion of the carrier. From this, it can be seen that the torque fluctuation is due to the difference in the wafer center position caused by the planetary motion of the carrier, and it can be seen that the change in this wafer center position can be appropriately output. Fig. 6 shows the average values of the torque acting on the upper surface plate and the motor power of the lower surface plate at each load weight. The upper surface plate torque shows the same value under the same load weight condition and is in a directly proportional relationship, indicating that appropriate measurements have been made. On the other hand, in the relationship between the load weight and the power, due to the phenomenon that the power gradually decreases, even if the polishing pressure is increased, it does not rise sufficiently, and the power values are different even under the same polishing pressure condition, and it is not in a completely directly proportional relationship. From this, it can also be seen that it is difficult to directly measure the lower surface plate torque from the power.

[0018] As described above, it is difficult to directly measure the lower surface plate torque from the power consumption or current value of the motor on the lower surface plate side. However, in double-sided polishing, since the polishing phenomena on the upper and lower surfaces of the workpiece are considered to be different, the method for estimating the lower platen torque was then examined. Although the variation in the power consumption of the drive motor due to the change in polishing resistance is smaller than the loss power due to the transmission path such as the gear and belt from the drive motor to the lower platen, if the loss power consumed in this transmission path can be estimated, the lower platen torque can be estimated based on it. Let the torque acting on the lower platen be T L , the power consumption of the drive motor be P, and the loss power consumed in the transmission path be P loss Then, Equation (1) holds. TIFF0007697663000003.tif13166 Here, κ is a proportionality constant. Therefore, obtaining the proportionality constant κ was considered. When performing co-grinding in which the upper platen and the lower platen are rubbed against each other without the workpiece, when the rotational speed of the drive motor is constant, the torques acting on the upper platen and the lower platen are balanced. Co-grinding was carried out under the conditions shown in the table of Fig. 7, and the relationship between the measured values of the power consumption of the drive motor and the platen torque is shown in Fig. 8. Fig. 8 shows the measured values when, after warm-up operation for 5 minutes, 30 minutes, and 60 minutes, the load on the upper platen was changed from the "0 N" state of idling only the lower platen to 20 N, 40 N, 60 N, 40 N, 20 N, and 0 N. Note that the power consumption of the drive motor indicates the average value for 60 seconds after 60 seconds have elapsed. From the graph showing this result, the relationship between the power consumption and the platen torque when the warm-up operation time was 60 minutes showed an almost linear relationship, but there was a large variation from the approximate straight line at 5 minutes and 20 minutes of warm-up operation. This is considered to be due to the decrease in the kinematic viscosity accompanying the temperature rise of the industrial lubricating oil and the change in tension accompanying the temperature rise of the power transmission belt. From the relationship between the power consumption of the drive motor and the platen torque in the stable state at 60 minutes of warm-up operation, κ = 0.48 Nm / J was determined in the above Equation (1).

[0019] Here, the value of the constant κ is a value determined by the lower turntable rotation speed and the transmission rate in the transmission path. With respect to the processing time, the loss power P in Equation (1) loss As shown in the power fluctuations at different warm-up operation times in the graph of FIG. 8, assuming that it decreases at a constant rate linearly, the relationship between the power consumption of the drive motor and the processing time is the relationship shown in FIG. 9. In FIG. 9, P pre is the average power consumption for one minute after one minute of idling before processing for two minutes, and P post is the average power consumption for one minute after one minute of idling after processing for two minutes. Here, when the processing time is t', the relationship of the following Equation (2) is obtained. TIFF0007697663000004.tif13166 In FIG. 9, when t' = 0 during idling before processing, B = P pre and thus the constant B is determined. When the processing time is T (minutes), P post = A(T + 2) + P pre and thus. Substituting this equation into Equation (2) gives the following Equation (3). TIFF0007697663000005.tif20166 In the above Equation (3), when t' is replaced with the processing start time t, t' = t - 0.5, so based on the processing start time, Equation (3) becomes the following Equation (4). TIFF0007697663000006.tif20166 From this Equation (4), when the value of the loss power P loss is obtained, based on this, the lower turntable torque T L can be obtained from the power consumption of the drive motor from Equation (1).

[0020] Next, the change in the lower turntable torque due to the presence or absence of dressing of the polishing pad was experimented. The polishing pad is Trizact Diamond Tile (#1200) manufactured by 3M, and 725N manufactured by Dazhi Chemical Co., Ltd. is used as the polishing liquid. The workpiece is borosilicate glass with a diameter and thickness of 25 mm and 1 mm, respectively. One workpiece is placed on each carrier, and four workpieces are processed simultaneously. The rotation speed of the lower platen is 12 min -1 , and the revolution of the carrier is 6 min -1 The ratio of the self-rotation speed was set to 1.5 The load was fixed at 60 N, and the polishing pressure acting on each wafer at this time was 27 kPa In addition, the processing time was 2 minutes or 4 minutes Up to a cumulative processing time of 8 minutes, the wafer was changed every 2 minutes to measure the polishing amount, but from 8 minutes to 32 minutes, the wafer was changed every 4 minutes to measure the polishing amount Figure 10 shows the torque waveforms of polishing performed immediately after dressing and only repeating processing without dressing The 20-second cycle variation is due to the interchange of the inner and outer circumferences of the planetary motion. However, focusing on the overall trend, it can be confirmed that the torque gradually decreases within 2 minutes in the processing performed immediately after dressing On the other hand, in the condition where the pad performance deteriorated without dressing, almost no decrease was observed and it was a constant value This is considered to be because the pad state deteriorates rapidly immediately after dressing, but the surface state stabilizes with the processing time From the measurement results of the polishing amount described later, it is considered that this torque reduction is caused by a decrease in the friction coefficient between the pad and the workpiece Next, focus on the 20-second cycle variation due to the interchange of the innermost and outermost circumferences by the planetary motion In the condition where the pad performance deteriorated, the torque decreased. However, the maximum and minimum values of the torque corresponding to when the workpiece was located at the outermost and innermost circumferences hardly changed. Since the most significant torque reduction occurred at the intermediate position between the outermost and innermost circumferences, it can be seen that the decrease in the friction coefficient between the pad and the workpiece occurs more prominently at the intermediate position than at the outer and inner circumferences of the pad This is considered to be because the cumulative residence time of the wafer is longer at the intermediate position of the lower platen due to the planetary motion of the carrier, and the deterioration of the pad progresses rapidly It is extremely important to maintain the state in which dressing is performed in double-sided grinding, and it is considered indispensable to uniformly advance the deterioration of the pad in order to improve the processing efficiency.

[0021] Fig. 11 shows a graph investigating the relationship between the torque of the output shaft calculated from the drive motor torque (horizontal axis) and the torque (vertical axis) obtained based on the force acting on the aforementioned holder. This graph shows the drive motor torque on the lower platen side and the torque on the upper platen side obtained based on the force acting on the holder when the upper platen and the lower platen are rubbed together and the load on the upper platen is changed from the "0 N" state of idling only on the lower platen to 20 N, 40 N, 60 N, 40 N, 20 N, 0 N. Also in this case, when the warm-up operation is performed for 60 minutes, the change in the output shaft torque on the lower platen side and the change in the upper platen torque obtained based on the force acting on the holder are nearly linear. From this, although the loss torque due to the transmission mechanism etc. on the lower platen side is considerably larger than the upper platen torque, by measuring the loss torque in advance by co-grinding, the lower platen torque can be estimated (measured) based on the above formula (1-1).

[0022] Fig. 12 shows a variation graph of the torque of the output shaft calculated from the drive motor torque (left vertical axis) and the torque (right vertical axis) obtained based on the force acting on the aforementioned holder in the co-grinding test when the warm-up operation time is changed to 5 minutes, 30 minutes, and 60 minutes under the condition of 60 N. When the warm-up operation is performed for 60 minutes, since the output shaft torque on the lower platen side during processing hardly changes, the change with the upper platen torque obtained based on the force acting on the holder as shown above is nearly linear, and the loss torque can be considered a constant. On the other hand, when the warm-up operation is 5 minutes, the output shaft torque on the lower platen side gradually decreases during processing. Therefore, when the warm-up operation is short, the lower platen torque can be estimated (measured) with high accuracy based on the above formula (1-1) by considering the loss torque as a linear or polynomial function.

Explanation of Signs

[0023] Upper platen 11 First stopper pin 11a Second stopper pin 11b Lower platen 12 Sun gear 12a Internal gear 12b Carrier 12c Wire 14 Air cylinder 15 First holder 16a Second holder 16b Workpiece W

Claims

1. In a double-sided polishing method for simultaneously polishing the upper and lower surfaces of a workpiece using a pair of upper and lower platens arranged opposite to each other vertically, a sun gear and an internal gear that impart a planetary motion to a carrier holding the workpiece are rotationally controlled by a drive motor, the upper platen has a constrained member and has a support member outside the upper platen, it has a sensor for measuring the contact force between the constrained member and the support member, A method for measuring the torque of the upper platen in double-sided polishing, characterized in that the rotational torque of the upper platen generated by the friction between the workpiece that performs a planetary motion together with the carrier is measured.

2. In a double-sided polishing method for simultaneously polishing the upper and lower surfaces of a workpiece using a pair of upper and lower platens arranged opposite to each other vertically, a sun gear and an internal gear that impart a planetary motion to a carrier holding the workpiece are rotationally controlled by a drive motor, the upper platen has a constrained member and has a support member outside the upper platen, it has a sensor for measuring the contact force between the constrained member and the support member, in a co-polishing state where no workpiece is interposed between the upper platen and the lower platen, A method for estimating the torque of the lower platen in double-sided polishing, characterized in that the loss power on the lower platen side is calculated by measuring the rotational torque generated on the upper platen, and the torque of the lower platen is estimated by the following formula (1). Here, T Ｌ = torque of the lower platen, κ = constant, P = power consumption of the drive motor on the lower platen side, P loss = indicates the power loss.

3. In a double-sided polishing method for simultaneously polishing the upper and lower surfaces of a workpiece using a pair of upper and lower platens arranged opposite to each other vertically, a sun gear and an internal gear that impart a planetary motion to a carrier holding the workpiece are rotationally controlled by a drive motor, the upper platen has a constrained member and has a support member outside the upper platen, it has a sensor for measuring the contact force between the constrained member and the support member, in a co-polishing state where no workpiece is interposed between the upper platen and the lower platen, A method for estimating the torque of the lower platen in double-sided polishing, characterized in that the loss torque on the lower platen side is calculated by measuring the rotational torque generated on the upper platen, and the torque of the lower platen is estimated by the following formula (1-1). Here, T Ｌ１ = Lower platen torque, T ＭＬ = Drive motor torque on the lower platen side, κ １ = Constant, T loss = Indicates the loss torque on the lower platen side.

4. A double-sided polishing machine for simultaneously polishing the upper and lower surfaces of a workpiece using a pair of upper and lower platens arranged opposite to each other vertically, the upper platen has pressing means for applying pressure toward the upper surface of the workpiece, the lower platen rotatably holds the workpiece to be polished, the upper platen side has a constrained member and has a support member outside the upper platen, A double-sided polishing machine, characterized by having means for measuring the contact force between the constrained member and the support member.

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