Method for double-sided grinding of workpiece

Abstract

The present invention provides a method for performing double-sided polishing on a workpiece made of a glass substrate, the method comprising the steps of: (1) starting polishing of the workpiece; (2) monitoring the rotating state of the workpiece in real time; and (3) when it is determined that the rotation state of the workpiece is out of the predetermined state in the step (2), the polishing condition is changed.

Description

Technical Field

[0001] The present invention relates to a method for double-sided polishing of a workpiece such as a glass substrate. Background Art

[0002] In order to effectively polish a glass substrate, a double-side polishing device is often used.

[0003] The double-side polishing apparatus includes an upper platen having an upper polishing pad and a lower platen having a lower polishing pad.

[0004] When a glass substrate (hereinafter also referred to as a "workpiece") is ground using such a double-sided grinding device, first, the workpiece to be ground is supported in a carrier disposed between an upper grinding pad of an upper platform and a lower grinding pad of a lower platform. Next, the upper platform and the lower platform are disposed in such a manner that the two grinding pads are in contact with the upper and lower surfaces of the workpiece, and pressure is applied to the upper and lower surfaces of the workpiece. Next, while applying rotation to the carrier, the upper platform and the lower platform are rotated in opposite directions to each other, thereby enabling the workpiece in the carrier to be ground from both sides.

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-74086

[0006] During double-sided grinding, the workpiece rotates freely in the carrier. However, due to the change of grinding conditions, the free rotation of the workpiece often stops. If the double-sided grinding process is performed in a state where the free rotation of the workpiece stops, there is a problem that the concave and convex of the workpiece becomes significant. In this case, it is difficult to obtain a high-quality glass substrate with suppressed thickness deviation.

[0007] Yet, in recent years, in the field of the double-sided grinding technology of semiconductor wafer, in order to improve the grinding accuracy of semiconductor wafer, proposed to be arranged on the adjustment process (patent documentation 1) of adjusting grinding conditions with original position (in-situ) in grinding.Therefore, consider that this technology is applied to the double-sided grinding of workpiece.

[0008] However, in this technology, the adjustment process is a process implemented at the final stage of the grinding process and constitutes only a very small part of the entire grinding process. Therefore, when grinding is continued in a state where the rotation of the workpiece is stopped, even if the adjustment process described in Patent Document 1 is implemented at the final stage of the subsequent grinding process, it is difficult to fully reduce the unevenness already formed on the workpiece.

[0009] As described above, in the field of double-side polishing technology for glass substrates, a double-side polishing method capable of obtaining a high-quality glass substrate with suppressed thickness variation has been sought. Summary of the invention

[0010] The present invention has been made in view of the above background, and an object of the present invention is to provide a double-side polishing method capable of obtaining a glass substrate with small thickness deviation.

[0011] In the present invention, a method is provided, which is a method for double-sided polishing of a workpiece made of a glass substrate, comprising the following steps:

[0012] (1) Start grinding the workpiece;

[0013] (2) monitoring the rotation state of the workpiece in real time; and

[0014] (3) When it is determined in the step (2) that the rotation state of the workpiece deviates from a predetermined state, the grinding conditions are changed.

[0015] The present invention can provide a double-side polishing method capable of obtaining a glass substrate having a small thickness deviation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a diagram schematically showing a longitudinal cross section of a double-side polishing device.

[0017] Figure 2 It is a plan view schematically showing a state where a carrier is arranged on a lower polishing pad of a lower platen of a double-side polishing apparatus.

[0018] Figure 3 This is a diagram schematically showing the flow of a method for double-side polishing a workpiece according to one embodiment of the present invention.

[0019] Figure 4 This is a diagram schematically showing an example of a configuration used when evaluating the rotation speed of a workpiece using a direct evaluation method in a method of double-side polishing a workpiece according to an embodiment of the present invention.

[0020] Figure 5 It is a schematic representation of the use of Figure 4 The structure shown is a graph showing the relationship between the grinding time and the angular velocity difference Δω that can be measured.

[0021] Figure 6 It is a figure which shows the point P1 - P5 on the surface of the glass substrate after grinding|polishing.

[0022] Figure 7 This is a diagram schematically showing an example of a map constructed in the indirect evaluation method in the method of double-side polishing a workpiece according to one embodiment of the present invention.

[0023] Figure 8 : This is a graph showing the time change of the angular velocity difference Δω measured in two polishing treatment batches.

[0024] Fig. 9 This is a diagram showing an example of a map constructed based on the relationship between the temperature difference ΔT measured by two temperature sensors and the index A.

[0025] Fig.10 1 is a diagram showing an example of a map constructed based on the relationship between the temperature difference ΔT measured by two temperature sensors and the symmetry index value B.

[0026] Fig.11 3 is a graph showing the changing behavior of a selected parameter (temperature difference ΔT) in the polishing process of Example 1.

[0027] Fig.12 3 is a graph showing the changing behavior of a selected parameter (temperature difference ΔT) in the polishing process of Example 2.

[0028] Fig.13 3 is a graph showing the changing behavior of a selected parameter (temperature difference ΔT) in the polishing process of Example 3.

[0029] Fig.14 3 is a graph showing the changing behavior of a selected parameter (temperature difference ΔT) in the polishing process of Example 4.

[0030] Fig.15 This is a graph showing an example of the relationship between the rotation speed of the lower platen and the selected parameter (temperature difference ΔT).

[0031] Fig.16 This is a graph showing an example of the relationship between the load on the upper platform and the selected parameter (temperature difference ΔT).

[0032] Fig.17 This is a graph showing an example of the relationship between the supply amount of slurry and the selected parameter (temperature difference ΔT). DETAILED DESCRIPTION

[0033] Hereinafter, one embodiment of the present invention will be described.

[0034] In one embodiment of the present invention, a method is provided, which is a method for double-sided grinding of a workpiece made of a glass substrate, comprising the following steps:

[0035] (1) Start grinding the workpiece;

[0036] (2) monitoring the rotation state of the workpiece in real time; and

[0037] (3) When it is determined in the step (2) that the rotation state of the workpiece deviates from a predetermined state, the grinding conditions are changed.

[0038] As described above, in the double-sided grinding of the workpiece, due to the change of grinding conditions, the free rotation of the workpiece often stops. In addition, if the double-sided grinding process is performed in a state where the free rotation of the workpiece stops, there is a problem that the concavity and convexity of the workpiece become significant. In this case, it is difficult to obtain a high-quality glass substrate with suppressed thickness deviation.

[0039] In contrast, in a double-sided polishing method according to an embodiment of the present invention, the rotation state of the workpiece is monitored in real time during the double-sided polishing of the workpiece. In addition, in a double-sided polishing method according to an embodiment of the present invention, when it is determined that the rotation state of the workpiece is out of a specified state, the polishing conditions can be quickly changed to return the rotation state of the workpiece to a desired state.

[0040] Therefore, in the double-side polishing method of one embodiment of the present invention, the workpiece can be kept free to rotate during the polishing period, and appropriate polishing conditions can be maintained. In addition, as a result, a glass substrate with small thickness deviation can be obtained after double-side polishing.

[0041] (One embodiment of the present invention)

[0042] Hereinafter, a method for double-side polishing of a workpiece according to an embodiment of the present invention will be described in more detail with reference to the drawings.

[0043] (Double-sided grinding device)

[0044] First, in order to better understand the features and structure of an embodiment of the present invention, refer to Figure 1 and Figure 2 The general structure and operation of a double-side polishing device will be described.

[0045] Figure 1 A schematic longitudinal cross-sectional view of a general double-sided polishing device is shown. Figure 2 Schematically represented in Figure 1 The double-side polishing apparatus shown has a carrier disposed therein.

[0046] like Figure 1 As shown, the double-side polishing apparatus 10 has a structure capable of polishing the upper surface and the lower surface of one or more workpieces at the same time.

[0047] Specifically, the double-sided polishing device 10 includes a base 20, a lower platform 30, an upper platform 40, a lifting mechanism 50, and a rotation transmission mechanism 60. The lower platform 30 is rotatably supported on the upper portion of the base 20, and a driving motor for driving the upper platform 40 and the like to rotate as a driving unit described later is installed inside the base 20.

[0048] A lower polishing pad (not shown) for polishing the lower surface of the workpiece is provided on the upper surface of the lower platform 30. In addition, an upper polishing pad (not shown) is provided on the lower surface of the upper platform 40 and is arranged opposite to the upper surface of the lower platform 30 and polishes the upper surface of the workpiece.

[0049] The lifting mechanism 50 is supported by a door-shaped frame 70 erected above the base 20, and has a lifting cylinder device 52 capable of lifting and lowering the upper platform 40. The lifting cylinder device 52 is installed at the center of the beam 72 of the frame 70 in a manner that can extend and retract in the downward direction. The piston rod 54 of the lifting cylinder device 52 extends downward.

[0050] A universal joint 55 connected to the central portion of the suspension component 80 is coupled to the lower front end portion of the piston rod 54. The suspension component 80 includes a plurality of pillars 80a extending in the up-down direction, and an annular mounting component 80b fixed to the lower end portion of the pillars 80a. The upper surface of the upper platform 40 is fixed to the lower surface of the annular mounting component 80b. Therefore, when the piston rod 54 of the lifting cylinder device 52 is driven upward or downward, the upper platform 40 connected to the piston rod 54 and the universal joint 55 via the suspension component 80 is also driven to rise or fall at the same time.

[0051] The upper platform 40 can be raised and lowered by the lifting cylinder device 52. In the raised state of the upper platform 40, a plurality of glass substrates and carriers (described later. See reference) on which the polishing process has been completed and which are placed on the upper surface of the lower platform 30 can be lifted and lowered. Figure 2 ) is taken out, and the other carrier 160 and the unground glass substrate are mounted on the upper surface of the lower platform 30.

[0052] In addition, the rotation transmission mechanism 60 has a coupling portion 62 formed in a cylindrical shape at the upper end of a motor drive shaft 61 of the drive motor of the upper platform 40 .

[0053] In addition, the rotation transmission mechanism 60 has a key (claw) 81 that can be engaged with a key groove (recess) 62a formed on the upper side of the coupling portion 62 of the center hole that passes through the upper platform 40. The key 81 protruding toward the inner circumference of the upper platform 40 is swingably mounted on the annular mounting member 80b through the support shaft 82 with the support shaft 82 as the swing center.

[0054] When the upper platform 40 is lowered, the key 81 is engaged with the key slot 62a, and when the upper platform 40 is raised, the key 81 is separated from the key slot 62a. When the key 81 is engaged with the key slot 62a, the driving torque of the driving motor of the upper platform 40 is transmitted to the upper platform 40, and the upper platform 40 rotates together with the coupling portion 62.

[0055] A drive motor that drives the upper surface plate 40 and the like to rotate is disposed inside the base 20 .

[0056] When a workpiece is polished using the double-side polishing apparatus 10 having such a structure, first, one or more carriers are prepared and placed on the lower platform 30 of the double-side polishing apparatus 10 .

[0057] Figure 2 A state in which five carriers 160 are arranged in total on the lower polishing pad 150 provided on the lower platen 30 is schematically shown.

[0058] Each carrier 160 is configured in a substantially disk shape and can hold a glass substrate to be polished, that is, a workpiece 170, inside. Figure 2 In the example shown, each carrier 160 holds a square-shaped workpiece 170 therein.

[0059] Here, a sun gear 32 is inserted from below into a rotation center hole on the upper surface of the lower platform 30 , and an internal gear 33 is provided on the inner side of the outer circumference of the upper surface of the lower platform 30 .

[0060] In addition, each carrier 160 has a gear 162 on the outer periphery, and the gear 162 is configured to mesh with the sun gear 32 and the internal gear 33 of the double-side polishing device 10 .

[0061] In addition, the shape of the workpiece 170 held by each carrier 160 is not particularly limited. Figure 2 Besides the square shape shown, a disc shape is also possible.

[0062] In addition, Figure 2 In the example shown, a total of five carriers 160 are disposed on the lower polishing pad 150 of the lower platen 30. However, this is only an example, and the number of carriers 160 used is not particularly limited. For example, the number of carriers 160 may be 1 to 4, or may be 6 or more.

[0063] Next, the upper platen 40 is lowered, and the upper polishing pad of the upper platen 40 is placed on each carrier 160 . As a result, the workpiece 170 held by each carrier 160 is sandwiched between the upper polishing pad of the upper platen 40 and the lower polishing pad 150 of the lower platen 30 .

[0064] In addition, the thickness of each carrier 160 is configured to be thinner than the thickness of each workpiece 170. Therefore, in a normal case, although the upper surface and the lower surface of each workpiece 170 are in contact with the upper polishing pad 150 and the lower polishing pad 150, respectively, the carrier 160 is not in contact with the upper polishing pad 150 or the lower polishing pad 150.

[0065] Next, by adjusting the relative height positions of the upper surface 40 and the lower surface 30 , a predetermined pressure is applied to the upper surface and the lower surface of each workpiece 170 .

[0066] Next, the sun gear 32 and the internal gear 33 rotate at a predetermined rotation ratio.

[0067] As described above, the gear 162 formed on the outer periphery of the carrier 160 meshes with the sun gear 32 and the internal gear 33. Therefore, the carrier 160 starts to rotate through the sun gear 32 and the internal gear 33, and revolves along the internal gear 33 (planetary drive).

[0068] Thus, the upper surface and the lower surface of each workpiece 170 are polished simultaneously by the upper polishing pad and the lower polishing pad 150 .

[0069] Furthermore, during the polishing of the workpiece 170 , polishing liquid may be supplied to the workpiece 170 from a supply port (not shown) provided on one side of the upper polishing pad and / or the lower polishing pad 150 , as required.

[0070] In the double-side polishing device 10 , through such operation, both surfaces of the workpiece 170 can be polished simultaneously.

[0071] (Method for double-sided grinding of a workpiece according to one embodiment of the present invention)

[0072] Next, refer to Figure 3 , an example of a method for double-sided polishing of a workpiece according to an embodiment of the present invention is described.

[0073] Figure 3 The flow of a method for double-side polishing a workpiece (hereinafter referred to as a “first method”) according to one embodiment of the present invention is schematically shown.

[0074] like Figure 3 As shown, the first method S100 starts from a grinding start step S110. In the grinding start step S110, for example, the double-side grinding apparatus 10 as described above is used to start grinding of the workpiece according to the first condition.

[0075] Next, in the rotation state determination step S120 of the first method S100, it is determined whether the rotation state of the workpiece is appropriate. Then, if it is determined that the rotation state of the workpiece is appropriate, the first method S100 enters the grinding maintenance step S130, and the grinding of the workpiece is continued under the first condition without changing the grinding condition.

[0076] On the other hand, when an abnormality is found in the rotation state of the workpiece in the rotation state determination step S120, the first method S100 proceeds to the condition changing step S140. Here, the grinding condition of the workpiece is changed from the first condition to the second condition.

[0077] Here, “abnormality in the rotation state of the workpiece” refers to a state in which the rotation speed of the workpiece decreases, in addition to a state in which the rotation of the workpiece stops.

[0078] In the condition changing step S140 , appropriate second polishing conditions are applied to the workpiece, the workpiece is returned to a desired rotation state, and appropriate polishing is continued.

[0079] Then, when the first method 100 enters the grinding completion judgment step S150, it is judged whether to continue or end the grinding of the workpiece. Here, if it is judged that the grinding of the workpiece is continued, the above steps S120 to S140 are repeated. On the other hand, in the grinding completion judgment step S150, if it is judged that the grinding of the workpiece is completed, the first method 100 enters the grinding completion step S160 to complete the grinding process of the workpiece.

[0080] The above is an overview of the process of the first method S100. However, in order to further improve the understanding of the first method S100, each process in the first method S100 is described in more detail below. In addition, in the following description, for the sake of clarity, the above-mentioned Figure 1-2 The reference numerals shown.

[0081] (Process S110)

[0082] In the polishing start step S110 , first, the workpiece 170 is set in the double-side polishing apparatus 10 . As described above, the workpiece 170 is disposed between the upper platen 40 and the lower platen 30 of the double-side polishing apparatus 10 in a state of being held by the carrier 160 .

[0083] Next, as described above, the upper platen 40 and the lower platen 30 are rotated, and double-side polishing of the workpiece 170 is started according to the first condition.

[0084] The first condition may include various values ​​related to double-side polishing of the workpiece 170 , such as the rotation speed of the upper platform 40 and the lower platform 30 , the temperature of the upper platform 40 and the lower platform 30 , the load of the upper platform 40 and the lower platform 30 , and the supply amount and temperature of the slurry.

[0085] In addition, under the first condition, each numerical value does not necessarily have to have a fixed value. On the contrary, in reality, each numerical value often varies within a predetermined range due to a deviation or the like.

[0086] (Step S120 to Step S130)

[0087] When the double-side polishing of the workpiece 170 is started, the rotation state of the workpiece 170 is evaluated in order to provide determination information in the rotation state determination step S120 .

[0088] The rotation state of the workpiece 170 can be determined by a direct evaluation method or an indirect evaluation method. Each evaluation method will be described below.

[0089] (Direct evaluation method)

[0090] In the direct evaluation method, a direct evaluation unit is used to directly observe the rotation speed of the workpiece 170. The direct evaluation unit includes, for example, a position detection sensor and an acceleration sensor. The acceleration sensor may also be an angular velocity sensor such as a gyro sensor.

[0091] Figure 4 A configuration example of a structure 220 used when evaluating the rotation speed of the workpiece 170 using the direct evaluation method is shown.

[0092] like Figure 4 As shown, when the rotation speed of the workpiece 170 is evaluated using the present structure 220 , the second carrier 180 is disposed inside each carrier 160 . The workpiece 170 is held in the second carrier 180 .

[0093] In addition, the number of carriers 160 and second carriers 180 included in the structure 220 is not particularly limited. For example, the number of carriers 160 and second carriers 180 can be one, two, three, or more than five. In addition, the number of workpieces 170 held on each second carrier 180 is also not particularly limited.

[0094] The carrier 16 and the second carrier 180 are provided with a direct evaluation unit.

[0095] For example, in Figure 4 In the illustrated example, a first gyro sensor 232a is mounted on each carrier 160, and a second gyro sensor 232b is mounted on each second carrier 180. Measurement information of the first gyro sensor 232a and the second gyro sensor 232b is wirelessly transmitted to an external receiver.

[0096] When the workpiece 170 is polished using the double-side polishing device 10 having such a structure 220 , the rotation speed of the workpiece 170 can be grasped in real time based on the information obtained by the first gyro sensor 232 a and the second gyro sensor 232 b .

[0097] Figure 5 An example of measurement results obtained in such a structure 220 is schematically shown.

[0098] exist Figure 5 In FIG. 1 , the horizontal axis is the time t from the start of grinding, and the vertical axis is the angular velocity difference Δω. The angular velocity difference Δω is the angular velocity ω measured by the second gyro sensor 232b. b The angular velocity ω measured by the first gyro sensor 232a a The difference is expressed as Δω=ω b -ω a .

[0099] exist Figure 5 In FIG. 1 , the dotted circle represents one cycle of the carrier 160 , that is, corresponds to the time (revolution time) for the carrier 160 to orbit the sun gear 32 once.

[0100] While the workpiece 170 continues to rotate freely as appropriate, Figure 5 As shown in the middle bold curve, the angular velocity difference Δω substantially repeats periodic changes. In contrast, when the free rotation of the workpiece 170 stops, Figure 5 As indicated by the thin straight line in the middle, the angular velocity difference Δω is a constant value.

[0101] Therefore, by measuring Figure 5 Such an angular velocity difference Δω can directly determine whether the workpiece 170 continues to rotate freely during the grinding process.

[0102] For example, when the variation range of the angular velocity difference Δω is smaller than a predetermined value, it can be determined that an abnormality has occurred in the rotation state of the workpiece 170 .

[0103] In the above example, the second carrier 180 is provided with the second gyro sensor 232b, but the second gyro sensor 232b may be directly mounted on the workpiece 170. In this case, the second carrier 180 may be omitted.

[0104] In the above example, the rotation state of the workpiece 170 is determined by using the angular velocity difference Δω between the two gyro sensors 232a and 232b. However, the rotation state of the workpiece 170 may be determined based on, for example, only the measurement value of the first gyro sensor 232a provided on the second carrier 180 or the workpiece 170.

[0105] (Indirect evaluation method)

[0106] In the indirect evaluation method, the rotation state of the workpiece 170 is predicted based on the measurable parameter. In addition, the determination in the rotation state determination step S120 is performed based on the prediction result.

[0107] For example, the rotation state of the workpiece 170 may be predicted by the following steps:

[0108] (i) determining an index indicating the state of the glass substrate after grinding;

[0109] (ii) constructing a map representing the relationship between the measured parameters and the indicators determined in (i);

[0110] (iii) During the actual double-side polishing process, the rotation state of the workpiece is predicted with reference to the constructed map.

[0111] (i) to (iii) are described in detail below.

[0112] First, an index is introduced in (i). The index is selected from the physical property values ​​of the polished glass substrate, which change according to the rotation state (normal / abnormal) of the workpiece 170 being polished. For example, the index may be an index representing the in-plane symmetry of the thickness of the polished glass substrate (hereinafter referred to as "symmetry index value B").

[0113] The symmetry index value B is determined as follows.

[0114] like Figure 6 As shown, five points P1 to P5 are selected on the surface of the polished glass substrate 251. Point P1 is the center O of the glass substrate 251, and points P2 to P5 are points located at positions that are rotationally symmetrical with respect to the center O at 90°. In addition, the radial distance d of points P2 to P5 from the center O is not particularly limited, but the distance d is preferably in the range of 0.5D to 1.0D. Here, D is the radius of the glass substrate 251.

[0115] The heights of the glass substrate 251 at the points P1 to P5 are t1 to t5, respectively. The average height of the glass substrate 251 at the points P2 to P5 is t ave In addition, if the thickness deviation of the glass substrate 251 is set to TTV (Total Thickness Variation), the index represented by the following formula (1) can be used as an index representing the symmetry of the glass substrate 251. That is, it is judged that the smaller the index A is, the better the symmetry of the glass substrate 251 is, and conversely, the larger the index A is, the worse the symmetry of the glass substrate 251 is.

[0116] Index A = TTV - |t1 - t ave |(1)

[0117] In addition, the thickness deviation TTV of the glass substrate 251 is represented by the difference between the maximum height and the minimum height in the plane.

[0118] Formula (1) can be expressed as follows using a threshold value Tv:

[0119] When the index A≦threshold Tv, the symmetry of the glass substrate is good.

[0120] When the index A>threshold value Tv, the symmetry of the glass substrate is poor.

[0121] Therefore, when the symmetry index value B represented by the following formula (2) is introduced, it can be said that when the symmetry index value B is below 0, the symmetry of such glass substrate 251 is good, and when the symmetry index value B exceeds 0, the symmetry of such glass substrate 251 is poor.

[0122] Symmetry index value B = index A - threshold Tv (2)

[0123] Next, the measurement parameters in (ii) above are selected.

[0124] The measurement parameters are not particularly limited as long as they are variables related to the above-mentioned index. For example, according to the knowledge of the inventors of the present application, it is understood that among the temperature measurement values ​​obtained from the temperature sensors installed at various locations of the double-sided polishing device 10, there are values ​​that have a good correlation with the above-mentioned symmetry index value B. In particular, the temperature of the upper platform 40 and the temperature of the lower platform 30 show a high correlation with the symmetry index value B.

[0125] Hereinafter, the selected measurement parameters are referred to as “selected parameters”.

[0126] Next, a map is constructed based on the plotting of the measurement results of the “selected parameters” obtained in various actual polishing processes and the obtained symmetry index value B of the glass substrate 251 .

[0127] Figure 7 Represents an example of a constructed mapping.

[0128] In this map, the horizontal axis represents the selected parameter, and the vertical axis represents the symmetry index value B.

[0129] The set of selected parameters obtained in each grinding batch and the symmetry index value B of the glass substrate are plotted within the map.

[0130] exist Figure 7 In the example shown, it is found that by setting the selected parameter to be equal to or greater than the X value, the symmetry index value B can be made equal to or less than 0, that is, the in-plane symmetry of the thickness of the glass substrate after polishing can be improved.

[0131] As described above, the symmetry index value B is a parameter depending on the rotation state of the workpiece 170 during grinding, and tends to exceed 0 (zero) when the workpiece 170 is ground in an inappropriate rotation state (for example, a rotation stop state).

[0132] Therefore, in the actual grinding process, the selected parameters are included in Figure 7 During the period in the region above the X value in the map of , it can be predicted that the rotation of the workpiece 170 is in a normal state.

[0133] As described above, in the indirect evaluation method, by monitoring selected parameters during the grinding of the workpiece 170 and comparing the monitored values ​​with the pre-constructed map, it is possible to determine whether the rotation state of the workpiece 170 is normal.

[0134] As described above, in the rotation state determination step S120 , the rotation state of the workpiece 170 is evaluated using the direct evaluation method or the indirect evaluation method.

[0135] Then, when it is determined that the rotation state of the workpiece 170 is normal, the first method S100 proceeds to the next grinding maintenance step S130 to continue the grinding process under the first condition. In addition, the first method S100 proceeds to the grinding completion determination step S150.

[0136] On the other hand, when it is determined in the rotation state determination step S120 that the workpiece 170 is not rotating normally, the first method S100 proceeds to the condition changing step S140 .

[0137] (Process S140)

[0138] In the condition changing step S140 , the grinding conditions of the workpiece 170 are changed from the first conditions to the second conditions.

[0139] For example, at least one condition selected from the rotation speed of the upper and lower platforms 40 and 30 , the temperature of the upper and lower platforms 40 and 30 , the load of the upper and lower platforms 40 and 30 , and the supply amount and temperature of the slurry may be changed.

[0140] After the polishing condition is changed to the second condition, the first method S100 proceeds to the polishing completion determination step S150.

[0141] (Process S150)

[0142] When the first method S100 enters the grinding completion determination step S150 , it is determined whether to continue grinding the workpiece 170 .

[0143] The judgment criterion is not particularly limited. The judgment criterion may be, for example, the grinding time, and after a predetermined time has passed since the grinding start step S110, the grinding is judged to be completed. Alternatively, the judgment criterion may be, for example, the grinding amount of the workpiece 170, and when the workpiece 170 reaches a predetermined grinding amount, the grinding is judged to be completed. In addition, the grinding amount of the workpiece 170 can be determined based on the distance between the upper platform 40 and the lower platform 30 and / or the accumulated power of the grinder motor since the grinding start step S110. Alternatively, it is also possible to judge whether to continue the grinding of the workpiece 170 based on other judgment criteria.

[0144] In the grinding completion determination step S150 , if the grinding completion determination criterion is not satisfied, the first method S100 returns to the rotation state determination step S120 to again determine whether the workpiece 170 is rotating normally.

[0145] On the other hand, when it is determined in the polishing completion determination step S150 that polishing needs to be completed, the first method S100 proceeds to the polishing completion step S160 .

[0146] (Process S160)

[0147] When it is determined in the grinding completion determination step S150 that the grinding needs to be completed, the first method S100 proceeds to a grinding completion step S160 , where the grinding process is completed.

[0148] Through the above steps, the workpiece 170 can be double-sided polished.

[0149] In the first method S100, a cycle of the rotation state determination step S120 to the grinding completion determination step S150 can be implemented. Therefore, in the first method S100, the problem of continuing to grind the workpiece 170 in a state where the free rotation of the workpiece 170 is stopped is suppressed, and the free rotation of the workpiece 170 during grinding is maintained. As a result, a high-quality glass substrate can be obtained after the grinding is completed.

[0150] In addition, it is considered that a major factor that hinders the free rotation of the workpiece 170 is thermal deformation of the upper surface plate 40 and / or the lower surface plate 30 .

[0151] Therefore, by effectively suppressing thermal deformation of the upper platen 40 and / or the lower platen 30 , more effective polishing can be performed in the first method S100 .

[0152] Specifically, the time required for the cycle of the rotation state determination step S120 to the grinding completion determination step S150 is Figure 3 It is effective that the sensing period In is smaller than the time constant τ of the thermal conduction of the upper platform 40 (or the lower platform 30. The same applies hereinafter).

[0153] The time constant τ (sec) of the heat conduction of the upper platform 40 is expressed by the following equation (3):

[0154] τ=mcR T =mcL / (kS) (3)

[0155] Here, m is the mass of the upper platform 40 (kg), c is the specific heat of the upper platform 40 (Jkg －1 K －1 ), R Tis the thermal resistance (K·sec / J), L is the thickness of the upper platform (mm), k is the thermal conductivity of the upper platform 40 (Wmm －1 K －1 ), S is the area of ​​the upper platform 40 (mm 2 ).

[0156] By setting the sensing period In<time constant τ, more efficient polishing can be performed.

[0157] Example

[0158] Hereinafter, examples of the present invention will be described.

[0159] (Example of measurement data using the direct evaluation method)

[0160] In the double-sided grinding of the workpiece by the double-sided grinding device, the above Figure 4 The structure 220 shown evaluates the rotation state of the workpiece.

[0161] Figure 8 Indicates the measurement results.

[0162] exist Figure 8 In the figure, the horizontal axis is the grinding time and the vertical axis is the angular velocity difference Δω. Figure 8 2 shows the measurement results of two polishing treatment batches (batch A and batch B). In treatment batch A, the angular velocity difference Δω changes periodically. On the other hand, in treatment batch B, the angular velocity difference Δω shows a substantially constant value.

[0163] It can be seen from this that the workpiece continued to rotate freely as desired during the grinding process in the processing batch A. On the other hand, in the processing batch B, it was found that the workpiece stopped.

[0164] In fact, in each lot, the state of the glass substrate after the grinding process was evaluated, and it was confirmed that the thickness deviation TTV of the glass substrate in lot A was smaller than that of the glass substrate in lot B.

[0165] (Example of constructing a mapping using the indirect evaluation method)

[0166] According to the following steps, a mapping that can be used in the above-mentioned indirect evaluation method is constructed.

[0167] (First Mapping)

[0168] First, based on the thickness deviation TTV and Figure 6 The index A is determined according to the above formula (1) based on the height data at each position shown.

[0169] When determining the index A, the radial distances of points P2 to P5 on the glass substrate from the center O are d=0.95D.

[0170] Next, to construct the map, the horizontal axis of the map, the "selected parameter", was selected.

[0171] The selected parameter is the temperature difference ΔT between a first temperature sensor and a second temperature sensor of an upper polishing pad disposed on an upper platform of the double-sided polishing device.

[0172] Here, the first temperature sensor is disposed at a position 625 mm away from the central axis of the upper platform in the radial direction, and the second temperature sensor is disposed at a position 1063 mm away from the central axis of the upper platform in the radial direction.

[0173] Next, a map is constructed based on the relationship between the measurement results of the “selected parameters” obtained in the actual polishing process and the index A described above.

[0174] exist Fig. 9 An example of the constructed mapping (hereinafter referred to as “first mapping”) is shown.

[0175] In the first map, the horizontal axis represents the average value of the temperature difference ΔT between the temperature of the first temperature sensor and the temperature of the second temperature sensor within 5 minutes before the end of all polishing steps, and the vertical axis represents the value of the index A.

[0176] In the first map, a pair of the index A obtained from the formula (1) and the temperature difference ΔT in the glass substrates obtained in each polishing batch is plotted.

[0177] As can be seen from the first map, the plotted groups are roughly divided into the first group on the upper side and the second group on the lower side. In addition, the first group and the second group can be divided by plotting a horizontal boundary line in the range of -1.05 μm to -0.580 μm of the index A. This boundary line corresponds to the threshold value Tv in the above formula (2).

[0178] In addition, the boundary X between the two sets of horizontal axes is a position where the temperature difference ΔT=-0.3°C.

[0179] It can be seen from the first mapping that when the temperature difference ΔT is less than -0.3°C, the symmetry of the glass substrate after grinding is reduced.

[0180] Here, in Fig. 9 , the value of index A of the second group is approximately twice the value of index A of the first group.

[0181] In this regard, consider the following situation.

[0182] As a main form of glass substrate with good symmetry, it is assumed that Figure 6 The case where the thickness t1 of the center O (point P1) of the glass substrate is greater than the thicknesses t1 to t5 of the remaining four surrounding points (P2 to P5).

[0183] In this case,

[0184] Since TTV = (maximum thickness - minimum thickness),

[0185] becomes TTV=(t1-t min )(4) formula.

[0186] Here, t min It is the minimum thickness among the surrounding 4 points (P2~P5).

[0187] As mentioned above, due to

[0188] Index A = TTV - |t1 - t ave |(1), thus becoming

[0189] Index A = (t1 - t min )-(t1-t ave )

[0190] =t ave -t min =(t max -t min ) / 2(5).

[0191] Here max It is the maximum thickness among the surrounding 4 points (P2 to P5).

[0192] On the other hand, in a glass substrate that does not have good symmetry, the cross section is substantially wedge-shaped, with the center O as the midpoint and the thickness being the largest at one of the two ends (t max ), the thickness becomes minimum at the other end (t min ).

[0193] In this case, due to

[0194] TTV=(t max -t min )(6) Formula,

[0195] |t1-t ave | is almost zero, so it becomes

[0196] Index A = TTV - |t1 - t ave |=(t max -t min )(7) formula.

[0197] As a result, it can be said that the index A tends to be twice as high in a glass substrate without good symmetry as in a glass substrate with good symmetry.

[0198] In addition, even in the other main morphology of the glass substrate with good symmetry, i.e. Figure 6 The same result can be obtained even when the thickness t1 of the center O (point P1) of the glass substrate is smaller than the thicknesses t1 to t5 of the remaining four surrounding points (P2 to P5).

[0199] Thus, when the index A is used, in the constructed map, the value of the index A in the abnormal rotation region (second group) tends to be approximately twice the value of the index A in the normal rotation region (first group).

[0200] (Second Mapping)

[0201] Next, the second mapping is constructed using the above formula (2).

[0202] Fig.10 Represents the constructed second map.

[0203] In the second map, the horizontal axis is the temperature difference ΔT similarly to the first map. On the other hand, the vertical axis is the symmetry index value B represented by equation (2).

[0204] In the second mapping, the symmetry index value B is binarized and displayed as 1 and 0. Here, "0" indicates that the symmetry index value B represented by formula (2) is less than 0, and "1" indicates that the symmetry index value B represented by formula (2) exceeds 0. The threshold value Tv of formula (2) is -1.05 μm.

[0205] It can also be seen from the second mapping that when the temperature difference ΔT is less than −0.3° C., the symmetry of the glass substrate after grinding is reduced.

[0206] Therefore, by using the first map and / or the second map, it is possible to determine whether the rotation of the workpiece in the grinding step is normal.

[0207] Hereinafter, the result of performing double-side polishing of the workpiece while monitoring the rotation state of the workpiece will be described with reference to the second map.

[0208] (Example 1)

[0209] According to the first method, the double-side grinding device is used to grind the double-sides of the workpiece.

[0210] The workpiece was a glass substrate having a size of 300 mm in diameter and about 0.7 mm in thickness. In the rotation state determination step S120 , an indirect evaluation method was used.

[0211] As mentioned above Figure 3 As shown, in the first method, in the rotation state determination step S120, it is determined whether there is an abnormality in the rotation of the workpiece. In the indirect evaluation method, this determination is performed by monitoring a selected parameter.

[0212] exist Fig.11 The varying behavior of selected parameters in the grinding process is shown.

[0213] exist Fig.11 In the figure, the horizontal axis is the grinding time, and the left vertical axis is the selected parameter, i.e. Fig.10 The temperature difference ΔT is shown. In addition, Fig.11 In FIG. 1 , for reference, the temperature of the slurry supplied during polishing is indicated as the right axis of the graph.

[0214] exist Fig.11 In FIG. 1 , the horizontal dotted line (ΔT=-0.3°C; hereinafter referred to as "reference line U") indicates a reference for determining the rotation state of the workpiece. That is, when the temperature difference ΔT is lower than the reference line U, there is a possibility that the rotation of the workpiece is abnormal.

[0215] However, in this Example 1, during the entire grinding process, the temperature difference ΔT exceeds the reference line U. Therefore, in Example 1, in the rotation state determination step S120 , the rotation of the workpiece is determined to be normal.

[0216] In addition, as a result, in Example 1, in the rotation state determination step S120, the polishing conditions are not changed, and the first method proceeds to the polishing maintenance step S130. Then, after a predetermined polishing time (10 minutes) has passed, a determination is made as to whether the polishing is completed in the polishing completion determination step S150, and in the polishing completion step S150, the polishing process is completed.

[0217] After the polishing process, the symmetry index value B of the obtained glass substrate was measured. As a result, the symmetry index value B=-0.195, and the glass substrate had sufficient symmetry.

[0218] (Example 2)

[0219] By the same method as in Example 1, the workpiece was double-sided ground.

[0220] exist Fig.12 The varying behavior of selected parameters in the grinding process is shown.

[0221] exist Fig.12 In the figure, the horizontal axis is the grinding time and the left vertical axis is the selected parameter, namely the temperature difference ΔT. Fig.12 In FIG. 1 , for reference, the temperature of the slurry supplied during polishing is indicated as the right axis of the graph.

[0222] like Fig.12 As shown, in Example 2, after about 1500 seconds, the monitored temperature difference ΔT is lower than the reference line U.

[0223] Therefore, in Example 2, at this time, the rotation of the workpiece is determined to be abnormal. That is, the first method enters the condition change step S140 from the rotation state determination step S120 to change the grinding conditions. In addition, in Example 2, the grinding conditions of the workpiece are changed by increasing the temperature of the supplied slurry (refer to Fig.12 of the slurry temperature).

[0224] As a result, it is confirmed that the temperature difference ΔT exceeds the reference line U again and returns to the normal range. Then, the first method determines the completion of grinding in the grinding completion determination step S150 after a predetermined grinding time (10 minutes) has passed, and completes the grinding process in the grinding completion step S150.

[0225] After the polishing process, the symmetry index value B of the obtained glass substrate was measured. As a result, the symmetry index value B=-0.067, and the glass substrate had sufficient symmetry.

[0226] In addition, in the double-sided polishing device used, the mass m of the upper platform is 363 kg and the specific heat c is 0.59×10 3 Jkg －1 K －1 , the thermal conductivity k is 16.7×10 －3 W －1 K －1 , the area S is 1.01×10 6 mm 2 , thickness L is 45mm.

[0227] Therefore, the time constant τ of the heat conduction of the upper platen 40 expressed by the above formula (3) is about 580 seconds. In contrast, the time required for the cycle of the rotation state determination step S120 to the grinding completion determination step S150 is Figure 3 The sensing period In in is 2 minutes or less. Therefore, the sensing period In is sufficiently smaller than the time constant τ.

[0228] (Example 3)

[0229] By the same method as in Example 1, the workpiece was double-sided ground.

[0230] exist Fig.13 The varying behavior of selected parameters in the grinding process is shown.

[0231] exist Fig.13 In the figure, the horizontal axis is the grinding time and the left vertical axis is the selected parameter, namely the temperature difference ΔT. Fig.13 In FIG. 1 , for reference, the temperature of the slurry supplied during polishing is indicated as the right axis of the graph.

[0232] like Fig.13As shown, in Example 3, the temperature difference ΔT was monitored to be lower than the reference line U after about 2200 seconds from the start of grinding.

[0233] Therefore, in Example 3, at this time, the rotation of the workpiece is determined to be abnormal. That is, the first method enters the condition changing step S140 from the rotation state judging step S120 to change the grinding conditions. In addition, in Example 3, the grinding conditions of the workpiece are changed by increasing the temperature of the supplied slurry (refer to Fig.13 The rise in slurry temperature after 2200 seconds).

[0234] As a result, it was confirmed that the temperature difference ΔT exceeded the reference line U again and returned to the normal range.

[0235] Then, after about 4200 seconds from the start of polishing, the temperature difference ΔT was monitored to be lower than the reference line U again.

[0236] Therefore, in Example 3, at this time, the rotation of the workpiece is judged to be abnormal, and the grinding conditions are changed again. In addition, here, the grinding conditions of the workpiece are also changed by increasing the temperature of the supplied slurry (refer to Fig.13 The rise in slurry temperature after 4000 seconds).

[0237] In the first method, after a predetermined polishing time (90 minutes) has elapsed, the polishing completion is determined in the polishing completion determination step S150, and the polishing process is completed in the polishing completion step S150.

[0238] After the polishing process, the symmetry index value B of the obtained glass substrate was measured. As a result, the symmetry index value B=-0.127, and the glass substrate had sufficient symmetry.

[0239] Furthermore, in Example 3, the sensing period In is also 2 minutes or less. Therefore, the sensing period In is sufficiently shorter than the time constant τ.

[0240] (Example 4)

[0241] The workpiece was double-sided polished by a conventional method. The double-sided polishing device and the shape of the workpiece used were the same as those in Example 1.

[0242] exist Fig.14 The varying behavior of selected parameters in the grinding process is shown.

[0243] exist Fig.14 In the figure, the horizontal axis is the grinding time and the left vertical axis is the selected parameter, namely the temperature difference ΔT. Fig.14 In FIG. 1 , for reference, the temperature of the slurry supplied during polishing is indicated as the right axis of the graph.

[0244] like Fig.14As shown, in Example 4, the temperature difference ΔT was monitored to be lower than the reference line U after about 2600 seconds from the start of grinding.

[0245] However, in Example 4, the workpiece is ground to the end according to the grinding conditions set initially, as in the conventional method.

[0246] After the polishing process, the symmetry index value B of the obtained glass substrate was measured. As a result, it was found that the symmetry index value B=-1.301, and the symmetry of the glass substrate was not very good.

[0247] In this way, it was confirmed that a glass substrate with small thickness deviation was obtained by double-sided polishing of the workpiece using the first method.

[0248] In Examples 2 and 3, in the condition changing step S140 , the polishing conditions were changed by changing the slurry temperature.

[0249] However, this is only an example, and in the condition changing step S140, the grinding conditions may also be changed by changing other control factors. The grinding conditions may also be changed, for example, according to the rotation speed of the upper and lower platforms, the temperature of the upper and lower platforms, the load of the upper and lower platforms, and the supply amount of the slurry.

[0250] exist Figure 15 to Figure 17 An example of control factors that affect the selected parameter (ie, the above-mentioned temperature change ΔT) is shown in FIG.

[0251] exist Fig.15 The relationship between the rotation speed of the lower platform and the temperature change ΔT is shown in FIG. Fig.16 The relationship between the load on the upper platform and the temperature change ΔT is shown in Fig.17 Graph 2 shows the relationship between the amount of slurry supplied and the temperature change ΔT.

[0252] According to these graphs, it can be said that the value of the selected parameter can be increased or decreased by changing at least the rotation speed of the lower table, the load of the upper table, and the supply amount of the slurry.

[0253] This application claims priority based on Japanese Patent Application No. 2022-099769 filed on June 21, 2022, the entire contents of which are incorporated herein by reference.

[0254] Description of Reference Numerals

[0255] 10...double-sided grinding device; 20...base; 30...lower platform; 32...sun gear; 33...internal gear; 40...upper platform; 50...lifting mechanism; 52...lifting cylinder device; 54...piston rod; 55...universal joint; 60...rotation transmission mechanism; 61...motor drive shaft; 62...joint; 62a...keyway; 70...frame; 72...beam; 80...suspension member; 80a...pillar; 80b...annular mounting member; 81...key; 82...support shaft ; 150...lower polishing pad; 160...carrier; 162...gear; 170...workpiece; 180...second carrier; 220...structure; 232a...first gyro sensor; 232b...second gyro sensor; 251...glass substrate; S100...first method; S110...polishing start step; S120...rotation state judgment step; S130...polishing maintenance step; S140...condition change step; S150...polishing completion judgment step; S160...polishing completion step.

Claims

1. A method for double-sided polishing of a workpiece made of a glass substrate, wherein: The process is as follows: (1) Start grinding the workpiece; (2) monitoring the rotation state of the workpiece in real time; as well as (3) When it is determined in the step (2) that the rotation state of the workpiece deviates from a predetermined state, the grinding conditions are changed.

2. The method according to claim 1, wherein: The method is implemented by a double-sided polishing device having an upper platform, a lower platform, and a supply unit for supplying slurry between the upper platform and the lower platform. In the process (3), at least one selected from the group consisting of the rotational speed of the upper platform and the lower platform of the double-sided polishing device, the temperature of the upper platform and the lower platform, the load of the upper platform and the lower platform, and the supply amount and temperature of the slurry is changed.

3. The method according to claim 1 or 2, wherein: In the step (2), the rotation state of the workpiece is directly measured.

4. The method according to claim 2, wherein: In the step (2), the rotation state of the workpiece is predicted based on a measurement value of a sensor provided in the double-side polishing device.

5. The method according to claim 4, wherein: The process (2) has the following steps: (i) determining an index indicating the state of the glass substrate after grinding; (ii) constructing a map representing the relationship between the measurement result based on the sensor and the index determined in (i); as well as (iii) referring to the constructed map, judging whether or not the workpiece is in a region indicating that the rotation state is abnormal based on the measurement result by the sensor.

6. The method according to claim 5, wherein: The index is an index indicating the symmetry of the glass substrate after the polishing.

7. The method according to claim 6, wherein: The sensor is one or more temperature sensors provided on the upper platen and / or the lower platen of the double-side polishing device.

8. The method according to claim 1 or 2, wherein: The method further comprises a step (4) of further changing the changed grinding conditions when it is determined that the rotation state of the workpiece deviates from a predetermined state after the step (3).

9. The method according to claim 8, wherein: The sensing period In of the step (3) and / or the step (4) is smaller than the time constant τ of the upper platform of the double-side polishing device expressed by the following formula: τ=mcL / (kS) Here, m is the mass of the upper platform (kg), c is the specific heat of the upper platform (Jkg －1 K －1 ), L is the thickness of the upper platform (mm), k is the thermal conductivity of the upper platform (Wmm －1 K －1 ), S is the area of ​​the upper platform (mm 2 ).

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