WO2023248960A1 - Method for polishing both sides of workpiece - Google Patents

Abstract

A method, for polishing both sides of a workpiece made of a glass substrate, comprises: (1) a step for starting polishing of the workpiece; (2) a step for monitoring the rotational state of the workpiece in real time; and (3) a step for changing polishing conditions when it is determined in the step (2) above that the rotational state of the workpiece deviates from a predetermined state.

Description

How to polish both sides of a workpiece

The present invention relates to a method for polishing both sides of a workpiece such as a glass substrate.

A double-sided polishing machine is often used to efficiently polish glass substrates.

The double-sided polishing device has an upper surface plate having an upper polishing pad and a lower surface plate having a lower polishing pad.

When polishing a glass substrate (hereinafter also referred to as a "work") using such a double-sided polishing device, first, the gap between the upper polishing pad of the upper surface plate and the lower polishing pad of the lower surface plate must be polished. A workpiece to be polished is supported in a carrier placed in the carrier. Next, the upper surface plate and the lower surface plate are arranged so that both polishing 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, by rotating the upper surface plate and the lower surface plate in opposite directions while applying rotation to the carrier, the workpiece in the carrier can be polished from both sides.

Japanese Patent Application Publication No. 2018-74086

During double-sided polishing, the workpiece rotates freely in the carrier. However, due to variations in polishing conditions, free rotation of the workpiece may often stop. If the double-side polishing process proceeds while the free rotation of the workpiece is stopped, there is a problem in that the workpiece becomes noticeably uneven. In this case, it becomes difficult to obtain a high-quality glass substrate with suppressed thickness deviation.

Incidentally, in recent years, in the field of double-sided polishing technology for semiconductor wafers, in order to improve the polishing accuracy of semiconductor wafers, it has been proposed to provide an adjustment step for adjusting polishing conditions in-situ during polishing (Patent Document 1). . Therefore, it is conceivable to apply this technique to double-sided polishing of a workpiece.

However, in this technique, the adjustment process is a process carried out at the final stage of the polishing process, and only constitutes a small part of the entire polishing process. Therefore, if polishing is continued while the rotation of the workpiece is stopped, even if the adjustment process described in Patent Document 1 is performed at the end of the subsequent polishing process, the unevenness already formed on the workpiece cannot be sufficiently removed. It is difficult to reduce it.

As described above, in the field of double-sided polishing technology for glass substrates, there is still a need for a double-sided polishing method that can obtain high-quality glass substrates with suppressed thickness deviations.

The present invention has been made in view of this background, and an object of the present invention is to provide a double-sided polishing method that can obtain a glass substrate with a small thickness deviation.

The present invention provides a method for polishing both sides of a workpiece made of a glass substrate, comprising:
(1) The process of starting polishing the workpiece,
(2) monitoring the rotational state of the workpiece in real time;
(3) in the step (2), if it is determined that the rotational state of the workpiece deviates from a predetermined state, changing the polishing conditions;
A method is provided having the following.

The present invention can provide a double-sided polishing method that can obtain a glass substrate with small thickness deviation.

FIG. 2 is a diagram schematically showing a longitudinal section of a double-sided polishing device. FIG. 2 is a top view schematically showing a state in which a carrier is placed on a lower polishing pad of a lower surface plate of a double-sided polishing apparatus. 1 is a diagram schematically showing a flow of a method for polishing both sides of a work according to an embodiment of the present invention. FIG. 2 is a diagram schematically showing an example of a configuration used when evaluating the rotational speed of a workpiece using a direct evaluation method in a method for polishing both sides of a workpiece according to an embodiment of the present invention. 5 is a graph schematically showing the relationship between polishing time and angular velocity difference Δω that can be measured when using the configuration shown in FIG. 4. FIG. FIG. 3 is a diagram showing points P ₁ to P ₅ on the surface of the glass substrate after polishing. FIG. 2 is a diagram schematically showing an example of a map constructed in an indirect evaluation method in a method for polishing both sides of a work according to an embodiment of the present invention. It is a graph showing the time change of the angular velocity difference Δω measured in two types of polishing batches. 3 is a diagram showing an example of a map constructed from the relationship between the temperature difference ΔT measured by temperature sensors at two locations and an index A. FIG. 3 is a diagram showing an example of a map constructed from the relationship between the temperature difference ΔT measured by temperature sensors at two locations and the symmetry index value B. FIG. 3 is a graph showing the change behavior of the selected parameter (temperature difference ΔT) during the polishing process in Example 1. 3 is a graph showing the change behavior of the selected parameter (temperature difference ΔT) during the polishing process in Example 2. 3 is a graph showing the change behavior of the selected parameter (temperature difference ΔT) during the polishing process in Example 3. 12 is a graph showing the change behavior of the selected parameter (temperature difference ΔT) during the polishing process in Example 4. It is a graph showing an example of the relationship between the rotation speed of the lower surface plate and the selection parameter (temperature difference ΔT). It is a graph showing an example of the relationship between the load of the upper surface plate and the selection parameter (temperature difference ΔT). It is a graph showing an example of the relationship between the supply amount of slurry and the selection parameter (temperature difference ΔT).

An embodiment of the present invention will be described below.

In one embodiment of the present invention, there is provided a method for polishing both sides of a workpiece made of a glass substrate, the method comprising:
(1) The process of starting polishing the workpiece,
(2) monitoring the rotational state of the workpiece in real time;
(3) in the step (2), if it is determined that the rotational state of the workpiece deviates from a predetermined state, changing the polishing conditions;
A method is provided having the following.

As mentioned above, during double-sided polishing of a workpiece, the free rotation of the workpiece may often stop due to fluctuations in the polishing conditions. Further, if the double-side polishing process proceeds while the free rotation of the workpiece is stopped, there is a problem that the workpiece becomes noticeably uneven. In this case, it becomes difficult to obtain a high-quality glass substrate with suppressed thickness deviation.

In contrast, in the double-sided polishing method according to an embodiment of the present invention, the rotational state of the workpiece is monitored in real time during double-sided polishing of the workpiece. Furthermore, in the double-sided polishing method according to an embodiment of the present invention, if it is determined that the rotational state of the workpiece deviates from a predetermined state, the polishing conditions are promptly changed to bring the rotational state of the workpiece to the desired state. can be returned to.

Therefore, in the double-sided polishing method according to an embodiment of the present invention, free rotation of the workpiece is maintained throughout the polishing period, making it possible to maintain appropriate polishing conditions. Moreover, as a result, it becomes possible to obtain a glass substrate with small thickness deviation after double-sided polishing.

(One embodiment of the present invention)
Hereinafter, a method for polishing both sides of a workpiece according to an embodiment of the present invention will be described in more detail with reference to the drawings.

(Double-sided polishing device)
First, in order to better understand the features and configuration according to an embodiment of the present invention, the general configuration and operation of a double-sided polishing apparatus will be described with reference to FIGS. 1 and 2.

FIG. 1 shows a schematic vertical cross-sectional view of a general double-sided polishing device. Further, FIG. 2 schematically shows a state in which a carrier is placed in the double-sided polishing apparatus shown in FIG. 1.

As shown in FIG. 1, the double-sided polishing apparatus 10 has a configuration that can simultaneously polish the top and bottom surfaces of one or more workpieces.

Specifically, the double-sided polishing apparatus 10 includes a base 20, a lower surface plate 30, an upper surface plate 40, a lifting mechanism 50, and a rotation transmission mechanism 60. A lower surface plate 30 is rotatably supported on the upper part of the base 20, and a drive motor is attached inside the base 20 to rotationally drive an upper surface plate 40 and the like as a drive unit to be described later. .

A lower polishing pad (not shown) for polishing the lower surface of the workpiece is installed on the upper surface of the lower surface plate 30. Further, on the lower surface of the upper surface plate 40, an upper polishing pad (not shown) is installed, which is placed oppositely above the lower surface plate 30 and polishes the upper surface of the workpiece.

The elevating mechanism 50 is supported by a gate-shaped frame 70 that stands above the base 20, and has an elevating cylinder device 52 that can raise and lower the upper surface plate 40. The lifting cylinder device 52 is attached to the center of the beam 72 of the frame 70 so as to extend and contract in the hanging direction. The piston rod 54 of the lifting cylinder device 52 extends downward.

A universal joint 55 connected to the center of the hanging member 80 is coupled to the lower tip of the piston rod 54. The hanging member 80 includes a plurality of columns 80a extending in the vertical direction and an annular attachment member 80b fixed to the lower end of the columns 80a. The upper surface of the upper surface plate 40 is fixed to the lower surface of the annular attachment member 80b. Therefore, when the piston rod 54 of the lifting cylinder device 52 is driven upward or downward, the upper surface plate 40 connected to the piston rod 54, the universal joint 55, and the hanging member 80 is also driven at the same time. rise or fall.

The upper surface plate 40 can be raised and lowered by a lifting cylinder device 52. When the upper surface plate 40 is in the raised state, a plurality of glass substrates and carriers (described later, see FIG. 2) that have been subjected to the polishing process and placed on the upper surface of the lower surface plate 30 are taken out, and another carrier 160 and unpolished glass substrates are removed. can be attached to the upper surface of the lower surface plate 30.

Further, the rotation transmission mechanism 60 has a coupling portion 62 formed in a cylindrical shape at the upper end of the motor drive shaft 61 of the drive motor of the upper surface plate 40.

Furthermore, the rotation transmission mechanism 60 has a key (claw) 81 that can be fitted into a key groove (recess) 62a formed on the upper side surface of the coupling portion 62 that passes through the center hole of the upper surface plate 40. The key 81 protruding toward the inner circumferential side of the upper surface plate 40 is swingably attached to the annular mounting member 80b by the spindle 82, with the spindle 82 as the center of swing.

When the upper surface plate 40 is lowered, the key 81 fits into the key groove 62a, and when the upper surface plate 40 is raised, the key 81 is separated from the key groove 62a. In a state where the key 81 and the keyway 62a are fitted, the driving torque of the drive motor of the upper surface plate 40 is transmitted to the upper surface plate 40, and the upper surface plate 40 rotates together with the coupling portion 62.

A drive motor that rotationally drives the upper surface plate 40 and the like is arranged inside the base 20.

When polishing a work using the double-sided polishing apparatus 10 having such a configuration, first, one or more carriers are prepared. Further, a carrier is installed on the lower surface plate 30 of the double-sided polishing apparatus 10.

FIG. 2 schematically shows a state in which a total of five carriers 160 are placed on the lower polishing pad 150 placed on the lower surface plate 30.

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. For example, in the example shown in FIG. 2, each carrier 160 holds one square workpiece 170 inside.

Here, a sun gear 32 is inserted from below into the rotation center hole on the upper surface of the lower surface plate 30, and an internal gear 33 is provided inside the outer periphery of the upper surface of the lower surface plate 30.

Furthermore, each carrier 160 has a gear 162 on its outer periphery, and the gear 162 is configured to mesh with the sun gear 32 and internal gear 33 of the double-side polishing apparatus 10.

Note that the shape of the work 170 held by each carrier 160 is not particularly limited. For example, the workpiece 170 may have a circular disc shape other than a square shape as shown in FIG. 2.

In the example shown in FIG. 2, a total of five carriers 160 are arranged on the lower polishing pad 150 of the lower surface plate 30. However, this is just 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 6 or more.

Next, the upper surface plate 40 is lowered, and the upper polishing pad of the upper surface plate 40 is placed on top of each carrier 160. As a result, the work 170 held by each carrier 160 is held between the upper polishing pad of the upper surface plate 40 and the lower polishing pad 150 of the lower surface plate 30.

Note that the thickness of each carrier 160 is configured to be thinner than the thickness of each work 170. Therefore, although the upper surface and the lower surface of each workpiece 170 are in contact with the upper polishing pad and the lower polishing pad 150, respectively, in the normal case, the carrier 160 does not come into contact with the upper polishing pad or the lower polishing pad 150.

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

Next, sun gear 32 and internal gear 33 are rotated at a predetermined rotation ratio.

As mentioned 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 by the sun gear 32 and the internal gear 33, and is also revolved along the internal gear 33 (planetary drive).

As a result, the upper and lower surfaces of each workpiece 170 are simultaneously polished by the upper polishing pad and the lower polishing pad 150.

Note that during polishing of the workpiece 170, polishing liquid is supplied to the workpiece 170 from a supply port (not shown) provided on the side of the upper polishing pad and/or the lower polishing pad 150 as necessary. Good too.

In the double-sided polishing apparatus 10, both sides of the workpiece 170 can be polished simultaneously through such an operation.

(Method for polishing both sides of a workpiece according to an embodiment of the present invention)
Next, with reference to FIG. 3, an example of a method for polishing both sides of a work according to an embodiment of the present invention will be described.

FIG. 3 schematically shows the flow of a method for polishing both sides of a workpiece (hereinafter referred to as the "first method") according to an embodiment of the present invention.

As shown in FIG. 3, the first method S100 starts with a polishing start step S110. In the polishing start step S110, polishing of the workpiece is started under the first conditions using, for example, the double-sided polishing apparatus 10 as described above.

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. If it is determined that the rotational state of the workpiece is appropriate, the first method S100 proceeds to a polishing maintenance step S130, where polishing of the workpiece is continued under the first conditions without changing the polishing conditions. .

On the other hand, if an abnormality is found in the rotational state of the workpiece in the rotational state determination step S120, the first method S100 proceeds to the condition change step S140. Here, the polishing conditions for the workpiece are changed from the first conditions to the second conditions.

Here, "abnormality in the rotational state of the workpiece" means a state in which the rotational speed of the workpiece is decreasing as well as a state in which the rotation of the workpiece has stopped.

In the condition changing step S140, appropriate second polishing conditions are applied to the workpiece, the workpiece returns to the desired rotational state, and proper polishing is continued.

Thereafter, when the first method 100 proceeds to the polishing completion determination step S150, it is determined whether to continue polishing the workpiece or to complete it. If it is determined here that polishing should be continued, the above steps S120 to S140 are repeated. On the other hand, when it is determined in the polishing completion determination step S150 that polishing of the workpiece is completed, the first method 100 proceeds to a polishing completion step S160, and the polishing process of the workpiece is completed.

The above is an overview of the flow of the first method S100. However, in order to better understand the first method S100, each step in the first method S100 will be explained in more detail below. In the following description, for clarity, the reference numerals shown in FIGS. 1 and 2 described above will be used to represent each member.

(Step S110)
In the polishing start step S110, the workpiece 170 is first placed in the double-sided polishing apparatus 10. As described above, the workpiece 170 is placed between the upper surface plate 40 and the lower surface plate 30 of the double-sided polishing apparatus 10 while being held by the carrier 160.

Next, as described above, the upper surface plate 40 and the lower surface plate 30 are rotated, and double-sided polishing of the workpiece 170 is started under the first condition.

The first conditions include the rotation speed of the upper surface plate 40 and the lower surface plate 30, the temperature of the upper surface plate 40 and the lower surface plate 30, the load of the upper surface plate 40 and the lower surface plate 30, and the supply amount and temperature of slurry, etc. Various numerical values regarding double-sided polishing of the workpiece 170 may be included.

Note that in the first condition, each numerical value does not necessarily have to have one fixed value. Rather, in reality, each numerical value often fluctuates within a predetermined range due to variations and the like.

(Step S120 to Step S130)
When double-sided polishing of the workpiece 170 is started, the rotational state of the workpiece 170 is evaluated in order to provide judgment information in the rotational state judgment step S120.

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 explained below.

(Direct evaluation method)
In the direct evaluation method, the rotation speed of the workpiece 170 is directly observed using a direct evaluation means. Direct evaluation means include, for example, position detection sensors and acceleration sensors. The acceleration sensor may be an angular velocity sensor such as a gyro sensor.

FIG. 4 shows an example of a configuration 220 used when evaluating the rotation speed of the workpiece 170 using the direct evaluation method.

As shown in FIG. 4, when evaluating the rotation speed of the workpiece 170 using the present configuration 220, a second carrier 180 is placed inside each carrier 160. Workpiece 170 is held within second carrier 180.

Note that the number of carriers 160 and second carriers 180 included in the configuration 220 is not particularly limited. For example, there may be one, two, three, or five or more carriers 160 and second carriers 180, respectively. Further, the number of works 170 held on each second carrier 180 is not particularly limited either.

A direct evaluation means is installed in the carrier 160 and the second carrier 180.

For example, in the example shown in FIG. 4, a first gyro sensor 232a is attached to each carrier 160, and a second gyro sensor 232b is attached to each second carrier 180. The measurement information of the first gyro sensor 232a and the second gyro sensor 232b is wirelessly transmitted to an external receiver.

When the workpiece 170 is polished using the double-sided polishing apparatus 10 having such a configuration 220, the rotation speed of the workpiece 170 can be grasped in real time from the information acquired by the first gyro sensor 232a and the second gyro sensor 232b. Can be done.

FIG. 5 schematically shows an example of measurement results obtained with such a configuration 220.

In FIG. 5, the horizontal axis is the time t from the start of polishing, and the vertical axis is the angular velocity difference Δω. The angular velocity difference Δω is expressed as the difference between the angular velocity ω _b measured by the second gyro sensor 232b and the angular velocity ω _a measured by the first gyro sensor 232a, that is, Δω=ω _b −ω _a. be.

In FIG. 5, a broken line circle represents one period of the carrier 160, that is, it corresponds to the time for the carrier 160 to make one revolution around the sun gear 32 (revolution time).

When the workpiece 170 continues to rotate appropriately, the angular velocity difference Δω repeats substantially periodic fluctuations, as shown by the thick curve in FIG. On the other hand, when the free rotation of the workpiece 170 is stopped, the angular velocity difference Δω exhibits a constant value, as shown by the thin straight line in FIG.

Therefore, by measuring the angular velocity difference Δω as shown in FIG. 5, it is possible to directly determine whether the workpiece 170 continues to rotate freely during the polishing process.

For example, if the range of change in the angular velocity difference Δω is smaller than a predetermined value, it may be determined that an abnormality has occurred in the rotational state of the workpiece 170.

Although the above example describes a configuration in which the second gyro sensor 232b is installed on the second carrier 180, the second gyro sensor 232b may be directly attached to the workpiece 170. In that case, second carrier 180 may be omitted.

Furthermore, in the above example, the rotational state of the workpiece 170 was grasped using the angular velocity difference Δω between the two gyro sensors 232a and 232b. However, different from this, for example, the rotational state of the workpiece 170 may be grasped only from the measured value of the first gyro sensor 232a installed on the second carrier 180 or the workpiece 170.

(Indirect evaluation method)
In the indirect evaluation method, the rotational state of the workpiece 170 is predicted from measurable parameters. Further, based on this prediction result, a determination is made in the rotation state determination step S120.

For example, the rotational state of the workpiece 170 may be predicted by the following procedure:
(i) Defining an index representing the state of the glass substrate after polishing;
(ii) constructing a map representing the relationship between the measured parameters and the indicators defined in (i);
(iii) Predict the rotational state of the workpiece by referring to the constructed map during the actual double-sided polishing process.

Hereinafter, (i) to (iii) will be explained in detail.

First, in (i), an index is introduced. The index is selected from the physical property values of the glass substrate after polishing, the values of which change depending on the rotational state (normal/abnormal) of the workpiece 170 during polishing. The index may be, for example, an index representing the in-plane symmetry of the thickness of the glass substrate after polishing (hereinafter referred to as "symmetry index value B").

The symmetry index value B is determined as follows.

As shown in FIG. 6, five points P ₁ to P ₅ are selected on the surface of the glass substrate 251 after polishing. Point P ₁ is the center O of the glass substrate 251, and points P ₂ to P ₅ are points that are rotationally symmetrical with respect to the center O by 90 degrees. Note that the radial distance d of the points P ₂ to P ₅ 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.

Let the heights of the glass substrate 251 at each point P ₁ to P ₅ be t ₁ to t ₅ , respectively. Further, the average height of the glass substrate 251 at points P ₂ to P ₅ is defined as t _ave . Furthermore, if the thickness deviation of the glass substrate 251 is TTV (Total Thickness Variation), then the index expressed by the following equation (1) is
Index A=TTV-|t ₁ -t _ave | Formula (1)
can be used as an index representing the symmetry of the glass substrate 251. That is, it is determined 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.

Note that the plate thickness deviation TTV of the glass substrate 251 is expressed as the difference between the in-plane maximum height and minimum height.

Equation (1) can be expressed as follows using the threshold Tv:

When index A≦threshold Tv, the symmetry of the glass substrate is good,
When index A>threshold Tv, the symmetry of the glass substrate is poor.

Therefore, the symmetry index value B expressed by the following equation (2)

Symmetry index value B = Index A - Threshold Tv (2) Formula
is introduced, when the symmetry index value B is 0 or less, such a glass substrate 251 has good symmetry, and when the symmetry index value B exceeds 0, such a glass substrate 251 has good symmetry. You can say it's bad.

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

The measurement parameter is not particularly limited as long as it is a variable that correlates with the above-mentioned index. For example, according to the knowledge of the present inventors, some temperature measurement values obtained from temperature sensors installed at various locations in the double-sided polishing apparatus 10 have a good correlation with the symmetry index value B described above. is known to exist. In particular, the temperature of the upper surface plate 40, the temperature of the lower surface plate 30, etc. show a high correlation with the symmetry index value B.

The selected measurement parameters are hereinafter referred to as "selected parameters."

Next, a map is constructed from a set of plots 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.

FIG. 7 shows an example of the constructed map.

In this map, the horizontal axis is the selection parameter, and the vertical axis is the symmetry index value B.

In the map, a set of the selected parameters and the symmetry index value B of the glass substrate obtained in each polishing batch is plotted.

In the example shown in FIG. 7, by setting the selection parameter to the X value or more, the symmetry index value B can be made to be 0 or less, that is, the in-plane symmetry of the thickness of the glass substrate after polishing can be improved. It turns out that you can.

Further, as described above, the symmetry index value B is a parameter that depends on the rotational state of the workpiece 170 during polishing, and the workpiece 170 is polished under an inappropriate rotational state (for example, rotation stopped state). In some cases, it tends to exceed 0 (zero).

Therefore, in the actual polishing process, it can be predicted that the rotation of the workpiece 170 is in a normal state while the selected parameter is included in the region equal to or greater than the X value in the map of FIG.

In this way, in the indirect evaluation method, while polishing the workpiece 170, the selected parameters are monitored and the monitored values are compared with a pre-built map to determine whether the rotational state of the workpiece 170 is normal. can do.

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

Then, when it is determined that the rotational state of the workpiece 170 is normal, the first method S100 proceeds to the next polishing maintenance step S130, and the polishing process under the first condition is continued. Further, after that, the first method S100 proceeds to a polishing completion determination step S150.

On the other hand, if 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 change step S140.

(Step S140)
In the condition changing step S140, the polishing conditions for the workpiece 170 are changed from the first conditions to the second conditions.

For example, the rotation speed of the upper surface plate 40 and the lower surface plate 30, the temperature of the upper surface plate 40 and the lower surface plate 30, the load of the upper surface plate 40 and the lower surface plate 30, the supply amount and temperature of slurry, etc. At least one condition may be changed.

After changing the polishing conditions to the second conditions, the first method S100 proceeds to a polishing completion determination step S150.

(Step S150)
When the first method S100 proceeds to the polishing completion determination step S150, it is determined whether or not to continue polishing the workpiece 170.

The criteria for judgment are not particularly limited. The criterion is, for example, the polishing time, and the polishing may be determined to be completed after a predetermined period of time has elapsed from the polishing start step S110. Alternatively, the determination criterion may be, for example, the amount of polishing of the workpiece 170, and the polishing may be determined to be completed when the workpiece 170 reaches a predetermined amount of polishing. Note that the amount of polishing of the workpiece 170 can be grasped from the distance between the upper surface plate 40 and the lower surface plate 30, and/or the integrated power of the polisher motor from the polishing start step S110, etc. Alternatively, it may be determined whether to continue polishing the workpiece 170 based on other criteria.

In the polishing completion determination step S150, if the polishing completion determination criteria are not met, the first method S100 returns to the rotation state determination step S120, and it is determined whether the workpiece 170 is rotating normally.

On the other hand, if 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.

(Step S160)
If it is determined in the polishing completion determination step S150 that polishing needs to be completed, the first method S100 proceeds to a polishing completion step S160, where the polishing process is completed.

Through the above steps, both sides of the workpiece 170 can be polished.

In the first method S100, a loop from the rotational state determination step S120 to the polishing completion determination step S150 can be performed. Therefore, in the first method S100, the problem that the workpiece 170 continues to be polished while the free rotation of the workpiece 170 is stopped is suppressed, and the free rotation of the workpiece 170 during polishing is maintained. As a result, it is possible to obtain a high quality glass substrate after polishing is completed.

Note that the main factor that prevents the free rotation of the workpiece 170 is thought to be thermal deformation of the upper surface plate 40 and/or the lower surface plate 30.

Therefore, by efficiently suppressing thermal deformation of the upper surface plate 40 and/or the lower surface plate 30, it becomes possible to perform more efficient polishing in the first method S100.

Specifically, the time required for the loop from the rotational state determination step S120 to the polishing completion determination step S150, that is, the sensing period In in FIG. It is effective to make it smaller than τ.

The time constant τ (sec) of heat conduction of the upper surface plate 40 is expressed by the following equation (3):

τ=mcR _T =mcL/(kS) (3) Formula
Here, m is the mass (kg) of the upper surface plate 40, c is the specific heat of the upper surface plate 40 (Jkg ^-1 K ^-1 ), R _T is the thermal resistance (K sec/J), and L is, The thickness (mm) of the upper surface plate, k is the thermal conductivity (Wmm ⁻¹ K ⁻¹ ) of the upper surface plate 40, and S is the area (mm ² ) of the upper surface plate 40.

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

Examples of the present invention will be described below.

(Example of measurement data using direct evaluation method)
During double-sided polishing of the workpiece by the double-sided polishing apparatus, the rotation state of the workpiece was evaluated using the configuration 220 as shown in FIG. 4 described above.

The measurement results are shown in Figure 8.

In FIG. 8, the horizontal axis is the polishing time, and the vertical axis is the angular velocity difference Δω. FIG. 8 shows measurement results for two types of polishing batches (batch A and batch B). In processing batch A, the angular velocity difference Δω varied periodically. On the other hand, in processing batch B, the angular velocity difference Δω showed a substantially constant value.

From this, it can be seen that in processing batch A, the workpiece continued to freely rotate as desired during the polishing process. On the other hand, in processing batch B, it was found that the workpiece was stopped.

In fact, when we evaluated the state of the glass substrates after polishing in each batch, it was confirmed that the glass substrates in batch A had a smaller plate thickness deviation TTV than the glass substrates in batch B.

(Example of map construction for indirect evaluation method)
A map that can be used in the indirect evaluation method described above was constructed using the following steps.

(1st map)
First, the index A was determined from the thickness deviation TTV of the glass substrate after double-sided polishing and the height data at each position shown in FIG. 6 according to the above-mentioned equation (1).

When determining the index A, the radial distance from the center O of points P ₂ to P ₅ on the glass substrate was set to d=0.95D.

Next, in order to construct the map, we selected the horizontal axis of the map, that is, the "selection parameter."

The selection parameter was the temperature difference ΔT between the first temperature sensor and the second temperature sensor provided on the upper polishing pad of the upper surface plate of the double-sided polishing apparatus.

Here, the first temperature sensor is installed at a position of 625 mm in the radial direction from the central axis of the upper surface plate, and the second temperature sensor is installed at a position of 1063 mm in the radial direction from the central axis of the upper surface plate. will be installed.

Next, a map was constructed from the relationship between the measurement results of the "selected parameters" obtained in the actual polishing process and the index A described above.

FIG. 9 shows an example of the constructed map (hereinafter referred to as the "first map").

In the first map, the horizontal axis is the average temperature difference ΔT between the temperature at the first temperature sensor and the temperature at the second temperature sensor for 5 minutes before the end of the entire polishing process, and the vertical axis is the index A is the value of

In the first map, a set of index A obtained from equation (1) and temperature difference ΔT is plotted for the glass substrates obtained in each polishing batch.

From the first map, it can be seen that the groups of plots are roughly divided into the first group on the upper side and the second group on the lower side. Furthermore, it can be seen that the first group and the second group can be distinguished by drawing a horizontal boundary line in the range of the value of index A from −1.05 μm to −0.580 μm. This boundary line corresponds to the threshold Tv in equation (2) above.

Note that the boundary X of the horizontal axis between both groups was at a position where the temperature difference ΔT=-0.3°C.

From the first map, it can be seen that when the temperature difference ΔT is less than -0.3°C, the symmetry of the glass substrate after polishing decreases.

Here, in FIG. 9, the value of the index A in the second group is approximately twice the value of the index A in the first group.

In this regard, the following is considered.

One main form of a glass substrate that provides good symmetry is that the thickness t ₁ at the center O (point _{P 1} ) of the glass substrate in _FIG . A case where the thickness is greater than the thicknesses t ₁ to t ₅ is assumed.

in this case,

TTV = (maximum thickness - minimum thickness)

Therefore,

TTV=(t ₁ - t _min ) (4) Formula
becomes. Here, t _min is the minimum thickness among the four surrounding points (P ₂ to P ₅ ).

As aforementioned,

Index A=TTV-|t ₁ -t _ave | Formula (1)
Therefore,

Index A = (t ₁ - t _min ) - (t ₁ - t _ave )
= t _ave - t _min = (t _max - t _min )/2 Equation (5)
becomes. Here, t _max is the maximum thickness among the four surrounding points (P ₂ to P ₅ ).

On the other hand, in a glass substrate that does not have good symmetry, the cross section is approximately wedge-shaped, with the center O being the midpoint, the thickness is maximum (t _max ) at one end, and the minimum thickness at the other end. (t _min ).

in this case,

TTV=(t _max - t _min ) (6) Formula
and |t ₁ −t _ave | is almost zero, so

Index A=TTV-|t ₁ -t _ave |=(t _max -t _min ) Equation (7)
becomes.

As a result, it can be said that for glass substrates that do not have good symmetry, the index A tends to be twice as large as that for glass substrates that have good symmetry.

Note that another main form of the glass substrate that provides good symmetry is that the thickness t ₁ at the center O ₍ point P ₁ ) of the glass substrate in FIG _. ) is smaller than the thickness t ₁ to t ₅ , similar results can be obtained.

In this way, when index A is adopted, in the constructed map, the value of index A in the abnormal rotation region (group 2) is approximately twice the value of index A in the normal rotation region (group 1). There is a tendency to

(Second map)
Next, a second map was constructed using the above-mentioned equation (2).

FIG. 10 shows the constructed second map.

In the second map, the horizontal axis is the temperature difference ΔT, similar to the first map. On the other hand, the vertical axis is the symmetry index value B expressed by equation (2).

Note that in the second map, the symmetry index value B is binarized into 1 and 0. Among these, "0" indicates that the symmetry index value B expressed by equation (2) is 0 or less, and "1" indicates that the symmetry index value B expressed by equation (2) is 0. It means exceeding. Note that the threshold value Tv in equation (2) was set to -1.05 μm.

It can also be seen from the second map that when the temperature difference ΔT is less than -0.3°C, the symmetry of the glass substrate after polishing decreases.

Therefore, by using the first map and/or the second map, it is possible to determine whether the rotation of the workpiece during the polishing process is normal.

Hereinafter, with reference to the second map, the results of polishing both sides of the workpiece while monitoring the rotational state of the workpiece will be described.

(Example 1)
According to the first method described above, both sides of the workpiece were polished using a double-sided polishing device.

The workpiece was a glass substrate with dimensions of 300 mm in diameter and approximately 0.7 mm in thickness. In the rotation state determination step S120, an indirect evaluation method was adopted.

As shown in FIG. 3 described above, 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 indirect evaluation methods, this determination is also made by monitoring selection parameters.

FIG. 11 shows the change behavior of the selected parameters during the polishing process.

In FIG. 11, the horizontal axis is the polishing time, and the left vertical axis is the selected parameter, that is, the temperature difference ΔT shown in FIG. Note that in FIG. 11, for reference, the temperature of the slurry supplied during polishing is shown as the right axis of the figure.

In FIG. 11, the horizontal broken line (ΔT=-0.3°C; hereinafter referred to as "reference line U") indicates the criterion for determining the rotational state of the workpiece. That is, if the temperature difference ΔT is below the reference line U, there is a possibility that an abnormality has occurred in the rotation of the workpiece.

However, in this example 1, the temperature difference ΔT exceeds the reference line U throughout the polishing process. Therefore, in Example 1, the rotation of the workpiece was determined to be normal in the rotation state determination step S120.

Furthermore, as a result, in Example 1, the polishing conditions were not changed in the rotational state determination step S120, and the first method proceeded to the polishing maintenance step S130. Thereafter, after a predetermined polishing time (10 minutes) has elapsed, it is determined that polishing is complete in a polishing completion determination step S150, and the polishing process is completed in a polishing completion step S150.

After the polishing treatment, the symmetry index value B of the obtained glass substrate was measured. As a result, the symmetry index value B was -0.195, and sufficient symmetry was obtained for the glass substrate.

(Example 2)
Both sides of the workpiece were polished in the same manner as in Example 1.

FIG. 12 shows the change behavior of the selected parameters during the polishing process.

In FIG. 12, the horizontal axis is the polishing time, and the left vertical axis is the selected parameter, that is, the temperature difference ΔT. Note that in FIG. 12, for reference, the temperature of the slurry supplied during polishing is shown as the right axis of the figure.

As shown in FIG. 12, in Example 2, it was monitored that the temperature difference ΔT fell below the reference line U after about 1500 seconds.

Therefore, in Example 2, it was determined that the rotation of the workpiece was not normal at this timing. That is, in the first method, the process proceeds from the rotational state determining step S120 to the condition changing step S140, and the polishing conditions are changed. In Example 2, the workpiece polishing conditions were changed by increasing the temperature of the supplied slurry (see the increase in slurry temperature in FIG. 12).

As a result, it was confirmed that the temperature difference ΔT exceeded the reference line U again and returned to the normal range. Thereafter, in the first method, after a predetermined polishing time (10 minutes) has elapsed, it is determined that polishing is complete in a polishing completion determination step S150, and the polishing process is completed in a polishing completion step S150.

After the polishing treatment, the symmetry index value B of the obtained glass substrate was measured. As a result, the symmetry index value B was -0.067, and sufficient symmetry was obtained for the glass substrate.

In addition, in the double-sided polishing apparatus used, the mass m of the upper surface plate is 363 kg, the specific heat c is 0.59×10 ³ Jkg ⁻¹ K ⁻¹ , and the thermal conductivity k is 16.7× 10 ⁻³ Wmm ⁻¹ K ⁻¹ , area S is 1.01×10 ⁶ mm ² , and thickness L is 45 mm.

Therefore, the time constant τ of heat conduction of the upper surface plate 40 expressed by the above-mentioned equation (3) is approximately 580 sec. On the other hand, the time required for the loop from the rotational state determination step S120 to the polishing completion determination step S150, that is, the sensing period In in FIG. 3 was less than 2 minutes. Therefore, the sensing period In was sufficiently smaller than the time constant τ.

(Example 3)
Both sides of the workpiece were polished in the same manner as in Example 1.

FIG. 13 shows the change behavior of the selected parameters during the polishing process.

In FIG. 13, the horizontal axis is the polishing time, and the left vertical axis is the selected parameter, that is, the temperature difference ΔT. Note that in FIG. 13, for reference, the temperature of the slurry supplied during polishing is shown as the right axis of the figure.

As shown in FIG. 13, in Example 3, it was monitored that the temperature difference ΔT fell below the reference line U about 2200 seconds after the start of polishing.

Therefore, in Example 3, it was determined that the rotation of the workpiece was not normal at this timing. That is, in the first method, the process proceeds from the rotational state determining step S120 to the condition changing step S140, and the polishing conditions are changed. In Example 3, the workpiece polishing conditions were changed by increasing the temperature of the supplied slurry (see the increase in slurry temperature after 2200 seconds in FIG. 13).

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

Thereafter, about 4200 seconds after the start of polishing, it was monitored that the temperature difference ΔT fell below the reference line U again.

Therefore, in Example 3, it was determined that the rotation of the workpiece was not normal at this timing, and the polishing conditions were changed again. Here, too, the workpiece polishing conditions were changed by increasing the temperature of the supplied slurry (see the increase in slurry temperature after time 4000 seconds in FIG. 13).

In the first method, after a predetermined polishing time (90 minutes) has passed, it is determined that polishing is complete in a polishing completion determination step S150, and the polishing process is completed in a polishing completion step S150.

After the polishing treatment, the symmetry index value B of the obtained glass substrate was measured. As a result, the symmetry index value B was -0.127, and sufficient symmetry was obtained for the glass substrate.

Note that in Example 3 as well, the sensing cycle In was 2 minutes or less. Therefore, the sensing period In was sufficiently smaller than the time constant τ.

(Example 4)
The workpiece was polished on both sides using conventional methods. The double-sided polishing device used, the shape of the workpiece, etc. were the same as in Example 1.

FIG. 14 shows the change behavior of the selected parameters during the polishing process.

In FIG. 14, the horizontal axis is the polishing time, and the left vertical axis is the selected parameter, that is, the temperature difference ΔT. Note that in FIG. 14, for reference, the temperature of the slurry supplied during polishing is shown as the right axis of the figure.

As shown in FIG. 14, in Example 4, it was monitored that the temperature difference ΔT fell below the reference line U about 2600 seconds after the start of polishing.

However, in this example 4, the workpiece was polished to the end under the polishing conditions set at the beginning, as in the conventional case.

After the polishing treatment, the symmetry index value B of the obtained glass substrate was measured. As a result, the symmetry index value B was -1.301, indicating that the symmetry of the glass substrate was not very good.

In this way, it was confirmed that by polishing both sides of the workpiece using the first method, a glass substrate with a small thickness deviation could be obtained.

Note that in Examples 2 and 3, the polishing conditions were changed by changing the slurry temperature in the conditions changing step S140.

However, this is just an example, and in the condition changing step S140, the polishing conditions may be changed by changing another control factor. The polishing conditions may be changed depending on, for example, the rotational speed of the upper surface plate and the lower surface plate, the temperature of the upper surface plate and the lower surface plate, the load of the upper surface plate and the lower surface plate, the amount of slurry supplied, and the like.

FIGS. 15 to 17 show examples of control factors that influence the selection parameter (ie, the temperature change ΔT described above).

FIG. 15 shows the relationship between the rotation speed of the lower surface plate and the temperature change ΔT. FIG. 16 shows the relationship between the load on the upper surface plate and the temperature change ΔT. Further, FIG. 17 shows the relationship between the supply amount of slurry and the temperature change ΔT.

From these figures, it can be said that the value of the selection parameter can be increased or decreased by changing at least the rotational speed of the lower surface plate, the load of the upper surface plate, and the supply amount of slurry.

This application claims priority based on Japanese Patent Application No. 2022-099769 filed on June 21, 2022, and the entire contents of the same Japanese application are incorporated by reference into this application.

10 Double-sided polishing device 20 Base 30 Lower surface plate 32 Sun gear 33 Internal gear 40 Upper surface plate 50 Lifting mechanism 52 Lifting cylinder device 54 Piston rod 55 Universal joint 60 Rotation transmission mechanism 61 Motor drive shaft 62 Joint portion 62a Keyway 70 Frame 72 Beam 80 Hanging member 80a Support column 80b Annular mounting member 81 Key 82 Support shaft 150 Lower polishing pad 160 Carrier 162 Gear 170 Work 180 Second carrier 220 Configuration 232a First gyro sensor 232b Second gyro sensor 251 Glass substrate S100 First method S110 Polishing start process S120 Rotation state determination process S130 Polishing maintenance process S140 Condition changing process S150 Polishing completion determination process S160 Polishing completion process

Claims (9)

1. A method for polishing both sides of a workpiece made of a glass substrate,
   (1) The process of starting polishing the workpiece,
   (2) monitoring the rotational state of the workpiece in real time;
   (3) in the step (2), if it is determined that the rotational state of the workpiece deviates from a predetermined state, changing the polishing conditions;
   A method having.
2. The method is carried out by a double-sided polishing device having an upper surface plate, a lower surface plate, and a supply means for supplying slurry between the two,
   In the step (3), the rotation speed of the upper surface plate and the lower surface plate of the double-sided polishing apparatus, the temperature of the upper surface plate and the lower surface plate, the load of the upper surface plate and the lower surface plate, and the slurry 2. The method of claim 1, wherein at least one selected from the group consisting of supply amount and temperature is changed.
3. The method according to claim 1 or 2, wherein in the step (2), the rotational state of the workpiece is directly measured.
4. The method according to claim 2, wherein in the step (2), the rotational state of the workpiece is predicted from a measurement value by a sensor installed in the double-sided polishing apparatus.
5. The step (2) above is
   (i) a step of determining an index representing the state of the glass substrate after polishing;
   (ii) constructing a map representing the relationship between the measurement results by the sensor and the index defined in (i); and (iii) referring to the constructed map to determine the measurement results by the sensor. a step of determining whether the rotational state of the workpiece is in a region indicating that it is abnormal;
   The method according to claim 4, comprising:
6. The method according to claim 5, wherein the index is an index representing symmetry of the glass substrate after polishing.
7. The method according to claim 6, wherein the sensor is one or more temperature sensors installed on the upper surface plate and/or the lower surface plate of the double-sided polishing apparatus.
8. moreover,
   (4) If it is determined that the rotational state of the workpiece deviates from a predetermined state after the step (3), further changing the changed polishing conditions. The method described in.
9. The method according to claim 8, wherein the sensing period In of the step (3) and/or the step (4) is less than a time constant τ of the upper surface plate of the double-sided polishing apparatus expressed by the following formula: :
   
   τ=mcL/(kS)
   
   Here, m is the mass of the upper surface plate (kg), c is the specific heat of the upper surface plate (Jkg ⁻¹ K ⁻¹ ), L is the thickness of the upper surface plate (mm), and k is the mass of the upper surface plate (Jkg −1 K −1 ). The thermal conductivity of the surface plate (Wmm ⁻¹ K ⁻¹ ), S is the area (mm ² ) of the upper surface plate.

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