TW202401558A - 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

Method for grinding workpieces on both sides

The present invention relates to a method for double-sided grinding of a workpiece such as a glass substrate.

When effectively grinding and processing glass substrates, double-sided grinding devices are often used.

The double-sided polishing device includes an upper platen with an upper polishing pad and a lower platen with a lower polishing pad.

When using this double-sided polishing device to polish a glass substrate (hereinafter also referred to as the "workpiece"), first, in a carrier arranged between the polishing pad above the upper platen and the polishing pad below the lower platen , supports the workpiece that becomes the object to be ground. Next, the upper platen and the lower platen are arranged so that the two polishing pads are in contact with the upper and lower surfaces of the workpiece, and the upper and lower surfaces of the workpiece are pressed. Then, while applying rotation to the carrier, the upper platen and the lower platen are rotated in opposite directions to each other, whereby the workpiece in the carrier can be ground from both sides. [Prior technical literature] [Patent Document]

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

[Problem to be solved by the invention]

During double-sided grinding, the workpiece rotates freely in the carrier. However, due to changes in grinding conditions, the free rotation of the workpiece often stops. If the double-sided grinding step is performed while the free rotation of the workpiece is stopped, there is a problem that the unevenness of the workpiece becomes conspicuous. In this case, it is difficult to obtain a high-quality glass substrate in which thickness variation is suppressed.

However, in recent years, in the field of double-sided polishing technology of 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, consider applying this technology to double-sided grinding of workpieces.

However, in this technology, the adjustment step is performed at the final stage of the polishing step and constitutes only a very small part of the entire polishing step. Therefore, when grinding is continued while the rotation of the workpiece is stopped, even if the adjustment step described in Patent Document 1 is performed at the final stage of the subsequent grinding step, it is difficult to sufficiently reduce the unevenness formed on the workpiece.

As described above, in the field of double-side polishing technology for glass substrates, a double-side polishing method that can obtain a high-quality glass substrate with suppressed thickness variation has been sought.

The present invention was completed 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 small thickness variation. [Technical means to solve problems]

The present invention provides a method for double-side grinding a workpiece made of a glass substrate; and has the following steps: (1) Start grinding the workpiece; (2) Real-time monitoring of the rotation status of the above workpiece; and (3) In the step of (2) above, when it is determined that the rotation state of the workpiece deviates from the specified state, the polishing conditions are changed. [Effects of the invention]

In the present invention, a double-sided polishing method that can obtain a glass substrate with smaller plate thickness deviation can be provided.

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

In one embodiment of the present invention, a method is provided, which is to double-side grind a workpiece made of a glass substrate; and has the following steps: (1) Start grinding the workpiece; (2) Real-time monitoring of the rotation status of the above workpiece; and (3) In the step of (2) above, when it is determined that the rotation state of the workpiece deviates from the specified state, the polishing conditions are changed.

As mentioned above, during double-sided grinding of a workpiece, the free rotation of the workpiece often stops due to changes in grinding conditions. Furthermore, if the double-sided grinding step is performed while the free rotation of the workpiece is stopped, there is a problem that the unevenness of the workpiece becomes conspicuous. In this case, it is difficult to obtain a high-quality glass substrate in which thickness variation is suppressed.

On the other hand, in the double-side polishing method according to one embodiment of the present invention, the rotation state of the workpiece is monitored in real time during the double-side polishing of the workpiece. Furthermore, in the double-sided polishing method according to one embodiment of the present invention, when it is determined that the rotational state of the workpiece deviates from the specified state, the polishing conditions can be quickly changed to return the rotational state of the workpiece to the desired state.

Therefore, in the double-sided grinding method according to an embodiment of the present invention, the workpiece can be kept freely rotating throughout the grinding period and appropriate grinding conditions can be maintained. In addition, as a result, after double-side polishing, a glass substrate with smaller thickness variation can be obtained.

(One embodiment of the present invention) Hereinafter, a method for double-sided grinding of a workpiece according to an embodiment of the present invention will be described in more detail with reference to the drawings.

(Double-sided grinding device) First, in order to better understand the characteristics and structure of one embodiment of the present invention, the general structure and operation of a double-sided polishing device will be described with reference to FIGS. 1 and 2 .

Figure 1 shows a schematic longitudinal cross-sectional view of a general double-sided polishing device. In addition, FIG. 2 schematically shows a state in which a carrier is arranged in the double-sided polishing device shown in FIG. 1 .

As shown in FIG. 1 , the double-sided grinding device 10 is configured to simultaneously grind the upper surface and lower surface of one or more workpieces.

Specifically, the double-sided polishing device 10 includes a base 20 , a lower platen 30 , an upper platen 40 , a lifting mechanism 50 , and a rotation transmission mechanism 60 . The lower platen 30 is rotatably supported on the upper part of the base 20 , and a drive motor for rotationally driving the upper platen 40 and the like is installed inside the base 20 as a drive unit to be described later.

A grinding pad (not shown) for grinding the lower surface of the workpiece is provided on the upper surface of the lower platen 30 . In addition, a polishing pad (not shown) is provided on the lower surface of the upper platen 40 to face the upper surface of the lower platen 30 and polish the upper surface of the workpiece.

The lifting mechanism 50 is supported by the portal frame 70 standing above the base 20, and has a lifting cylinder device 52 that can lift the upper platen 40. The lifting cylinder device 52 is installed in the center of the beam 72 of the frame 70 so as to telescopically move in the vertical direction. The piston rod 54 of the lifting cylinder device 52 extends downward.

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

The upper pressure plate 40 can be lifted and lowered by the lifting cylinder device 52 . In the ascending state of the upper platen 40, the plurality of glass substrates and carriers (described later. Refer to Figure 2) placed on the upper surface of the lower platen 30 after the polishing step can be taken out, and other carriers 160 and unpolished ones can be removed. The glass substrate is installed on the upper surface of the lower platen 30 .

Furthermore, 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 platen 40 .

Furthermore, the rotation transmission mechanism 60 has a key (claw) 81 that can be fitted into a key groove (recessed portion) 62 a formed on the upper side of the coupling portion 62 penetrating the center hole of the upper pressure plate 40 . The key 81 protruding toward the inner peripheral side of the upper pressure plate 40 is swingably mounted on the annular mounting member 80 b with the support shaft 82 as the swing center.

When the upper platen 40 is lowered, the key 81 is fitted into the key groove 62a, and when the upper platen 40 is raised, the key 81 is separated from the key groove 62a. When the key 81 is engaged with the key groove 62a, the driving torque of the driving motor of the upper pressure plate 40 is transmitted to the upper pressure plate 40, and the upper pressure plate 40 rotates together with the coupling part 62.

A driving motor for rotating the upper platen 40 and other components is arranged inside the base 20 .

When using the double-sided grinding device 10 configured in this way to grind a workpiece, one or more carriers are first prepared. In addition, a carrier is provided on the lower platen 30 of the double-sided grinding device 10 .

FIG. 2 schematically shows a state in which a total of five carriers 160 are arranged on the lower polishing pad 150 provided on the lower platen 30 .

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

Here, the sun gear 32 is inserted into the rotation center hole on the upper surface of the lower pressure plate 30 from below, and an internal gear 33 is provided inside the outer circumference of the upper surface of the lower pressure 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 the internal gear 33 of the double-sided grinding device 10 .

In addition, the shape of the workpiece 170 held by each carrier 160 is not particularly limited. For example, in addition to the square shape shown in FIG. 2 , the workpiece 170 may also be in the shape of a disk.

Moreover, in the example shown in FIG. 2 , a total of five carriers 160 are arranged on the polishing pad 150 under the lower platen 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 can be 1 to 4, or more than 6.

Then, the upper platen 40 is lowered, and the polishing pad on the upper platen 40 is arranged on each carrier 160 . As a result, the workpiece 170 held on each carrier 160 is clamped between the polishing pad above the upper platen 40 and the polishing pad 150 below the lower platen 30 .

In addition, the thickness of each carrier 160 is configured to be thinner than the thickness of each workpiece 170 . Therefore, under normal circumstances, although the upper surface and the lower surface of each workpiece 170 contact the upper polishing pad and the lower polishing pad 150 respectively, the carrier 160 does not contact the upper polishing pad or the lower polishing pad 150 .

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

Next, the sun gear 32 and the internal gear 33 rotate at a designated 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 through the sun gear 32 and the internal gear 33 and revolves along the internal gear 33 (planetary drive).

Thereby, the upper surface and the lower surface of each workpiece 170 are simultaneously polished by the upper polishing pad 150 and the lower polishing pad 150 .

In addition, during polishing of the workpiece 170 , the polishing liquid can also be supplied to the workpiece 170 from the supply port (not shown) provided on the upper polishing pad and/or the lower polishing pad 150 side as needed.

In the double-sided grinding device 10, both sides of the workpiece 170 can be ground simultaneously through this action.

(Method for double-sided grinding of workpiece according to one embodiment of the present invention) Next, an example of a method for double-sided grinding of a workpiece according to an embodiment of the present invention will be described with reference to FIG. 3 .

FIG. 3 schematically shows the flow of a method for double-sided grinding of a workpiece according to an embodiment of the present invention (hereinafter referred to as the "first method").

As shown in FIG. 3 , the first method S100 starts from the polishing start step S110. In the grinding start step S110, for example, the double-sided grinding device 10 as described above is used to start grinding the workpiece under the first condition.

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. And, when it is determined that the rotation state of the workpiece is appropriate, the first method S100 proceeds to the polishing maintenance step S130, and the polishing conditions are not changed, and the polishing of the workpiece is continued while the first condition is kept unchanged.

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

Here, "abnormality in the rotational state of the workpiece" means a state in which the rotation speed of the workpiece is reduced in addition to the state in which the rotation of the workpiece is stopped.

In the condition changing step S140, appropriate second grinding conditions are applied to the workpiece, the workpiece returns to the desired rotation state again, and appropriate grinding is continued.

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

The above is an outline of the flow of the first method S100. However, in order to further improve the understanding of the first method S100, each step in the first method S100 will be described in more detail below. In addition, in the following description, for the sake of clarity, the reference numerals shown in the above-mentioned FIGS. 1 to 2 are used to represent each member.

(step S110) In the grinding start step S110 , the workpiece 170 is first set in the double-sided grinding device 10 . As mentioned above, the workpiece 170 is arranged between the upper platen 40 and the lower platen 30 of the double-sided grinding device 10 while being held on the carrier 160 .

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

The first condition may include the rotation speed of the upper platen 40 and the lower platen 30 , the temperature of the upper platen 40 and the lower platen 30 , the load of the upper platen 40 and the lower platen 30 , and the supply amount and temperature of the slurry, etc. Various values related to double-sided grinding of workpiece 170 .

In addition, under the first condition, each numerical value does not necessarily have a fixed value. On the contrary, in reality, there are many cases where each numerical value changes within the specified range due to deviations, etc.

(Step S120 to Step S130) When double-sided grinding of the workpiece 170 is started, the rotational state of the workpiece 170 is evaluated in order to provide determination information for the rotational state determination 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 is explained below.

(direct assessment method) In the direct evaluation method, a direct evaluation mechanism is used to directly observe the rotation speed of the workpiece 170 . Direct evaluation mechanisms include, for example, position detection sensors and acceleration sensors. The acceleration sensor may also be an angular velocity sensor such as a gyroscope sensor.

FIG. 4 shows an example of the structure 220 used when the direct evaluation method is used to evaluate the rotation speed of the workpiece 170 .

As shown in FIG. 4 , when the rotation speed of the workpiece 170 is evaluated by this structure 220 , the second carrier 180 is arranged inside each carrier 160 . The workpiece 170 is held in the second carrier 180 .

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 may be 1, 2, 3, or 5 or more respectively. In addition, the number of workpieces 170 held on each second carrier 180 is not particularly limited.

A direct evaluation mechanism is provided on the carrier 160 and the second carrier 180 .

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

When the double-sided grinding device 10 having such a structure 220 is used to grind the workpiece 170, the rotational speed of the workpiece 170 can be grasped in real time from information obtained from the first gyro sensor 232a and the second gyro sensor 232b.

An example of measurement results obtained with such a configuration 220 is schematically shown in FIG. 5 .

In Figure 5, the horizontal axis represents the time t since the start of grinding, and the vertical axis represents the angular velocity difference Δω. The angular velocity difference Δω is represented by the difference between the angular velocity ω b measured by the second gyro sensor 232 _b and the angular velocity ω _a measured by the first gyro sensor 232 a , that is, Δω=ω _b −ω _a .

In FIG. 5 , the dotted circle represents one cycle of the carrier 160 , that is, it corresponds to the time (revolution time) that the carrier 160 takes to revolve around the sun gear 32 .

When the workpiece 170 continues to freely rotate appropriately, as shown by the thick curve in FIG. 5 , the angular velocity difference Δω essentially changes periodically. On the other hand, when the free rotation of the workpiece 170 is stopped, as shown by the thin straight line in FIG. 5 , the angular velocity difference Δω shows a constant value.

Therefore, by measuring the angular velocity difference Δω as shown in FIG. 5 , it can be directly determined whether the workpiece 170 continues to rotate freely during the grinding process.

For example, when the change amplitude of the angular velocity difference Δω is less than a specified value, it may also be determined that the rotation state of the workpiece 170 is abnormal.

In addition, in the above example, the structure in which the second carrier 180 is provided with the second gyro sensor 232 b has been described, but the second gyro sensor 232 b may also be directly mounted on the workpiece 170 . In this case, the second carrier 180 can be omitted.

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

(indirect evaluation method) In the indirect evaluation method, the rotation state of the workpiece 170 is predicted from measurable parameters. Furthermore, based on the prediction result, the rotation state determination step S120 is performed.

For example, the rotation state of the workpiece 170 can also be predicted through the following sequence: (i) Determine indicators indicating the state of the polished glass substrate; (ii) construct a mapping representing the relationship between the measured parameter and the indicator determined in (i); and (iii) During the actual double-sided grinding process, the rotation state of the workpiece is predicted with reference to the constructed mapping.

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

First, import the indicator in (i). The index is selected from the physical property value of the polished glass substrate in such a way that the value changes according to the rotation state (normal/abnormal) of the workpiece 170 being polished. For example, the index may be an index indicating the in-plane symmetry of the thickness of the polished glass substrate (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 polished glass substrate 251 . Point P ₁ is the center O of the glass substrate 251 , and points P ₂ to P ₅ are points that are mutually 90° rotationally symmetrical with respect to the center O. In addition, the radial distance d between the points P ₂ to P ₅ and 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 height of the glass substrate 251 at each point P ₁ to P ₅ be t ₁ to t ₅ respectively. Moreover, let the average height of the glass substrate 251 at points _P2 to _P5 be _tave . Furthermore, assuming that the thickness variation of the glass substrate 251 is TTV (Total Thickness Variation), an index represented by the following formula (1) can be used as an index indicating 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.

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

Equation (1) can be expressed as follows using the threshold Tv: When the index A≦threshold Tv, the symmetry of the glass substrate is good; when the index A>threshold Tv, the symmetry of the glass substrate is poor. Therefore, when the symmetry index value B represented by the following formula (2) is introduced, it can be said that the symmetry of the glass substrate 251 is better when the symmetry index value B is 0 or less. When the property index value B exceeds 0, the symmetry of the glass substrate 251 is poor.

Next, select the measurement parameters in (ii) above.

The measurement parameters are not particularly limited as long as they are variables related to the above indicators. For example, according to the knowledge of the inventors of the present application, it has been found that among the temperature measurement values obtained from the temperature sensors installed in each place of the double-sided polishing device 10, there are some that have good correlation with the above-mentioned symmetry index value B. . In particular, the temperature of the upper platen 40 and the temperature of the lower platen 30 are highly correlated with the symmetry index value B.

The selected measurement parameters will be referred to as "selected parameters" below.

Next, a mapping is constructed from a plot of a combination 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 .

An example of the constructed mapping is shown in Figure 7.

In this mapping, the horizontal axis represents the selected parameter, and the vertical axis represents the symmetry index value B.

The set of selected parameters obtained in each grinding batch and the symmetry index value B of the glass substrate is depicted in the map.

In the example shown in FIG. 7 , it can be seen that by setting the selected parameter to be equal to or greater than the .

In addition, as mentioned above, the symmetry index value B is a parameter that depends on the rotational state of the workpiece 170 during grinding. When the workpiece 170 is polished in an inappropriate rotational state (for example, the rotational stop state), the symmetry index value B may exceed 0 (zero) tendency.

Therefore, during the actual grinding process, during the period when the selected parameters are included in the area above the X value in the map of FIG. 7 , the rotation of the workpiece 170 can be predicted to be in a normal state.

In this way, 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 mapping, it can be determined whether the rotation state of the workpiece 170 is normal.

As 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.

Moreover, 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. Then, the first method S100 proceeds to the grinding completion determination step S150.

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

(step S140) In the condition changing step S140, the polishing condition of the workpiece 170 is changed from the first condition to the second condition.

For example, the rotation speed of the upper platen 40 and the lower platen 30 , the temperature of the upper platen 40 and the lower platen 30 , the load of the upper platen 40 and the lower platen 30 , and the supply amount and temperature of the slurry are selected. at least 1 condition.

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

(step S150) When the first method S100 enters the grinding completion judgment step S150, it is judged here whether to continue grinding the workpiece 170.

The judgment criteria are not particularly limited. The determination criterion is, for example, polishing time, and it can be determined that polishing is completed after a specified time has elapsed since the polishing start step S110. Or, the judgment criterion is, for example, the grinding amount of the workpiece 170. When the workpiece 170 reaches the specified grinding amount, it can be judged that the grinding is completed. In addition, the grinding amount of the workpiece 170 can be grasped based on the distance between the upper platen 40 and the lower platen 30 and/or the accumulated power of the grinding machine motor since the grinding start step S110, etc. Alternatively, it may also be determined based on other judgment criteria whether to continue grinding the workpiece 170 .

In the grinding completion judgment step S150, if the grinding completion judgment criterion is not satisfied, the first method S100 returns to the rotation state judgment step S120 to judge again whether the workpiece 170 is normally rotated.

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.

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

Through the above steps, the workpiece 170 can be ground on both sides.

In the first method S100, a loop 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 while 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, after grinding is completed, a high-quality glass substrate can be obtained.

In addition, it is considered that the main reason that hinders the free rotation of the workpiece 170 is the thermal deformation of the upper platen 40 and/or the lower platen 30 .

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

Specifically, the time required for the cycle from the rotation state determination step S120 to the grinding completion determination step S150, that is, the sensing period In in FIG. 3 is smaller than the heat conduction of the upper platen 40 (or the lower platen 30, the same below). The time constant τ is more effective.

The time constant τ (sec) of heat conduction in the upper platen 40 is expressed by the following formula (3): Here, m is the mass of the upper platen 40 (kg), c is the specific heat of the upper platen 40 (Jkg ^-1 K ^-1 ), R _T is the thermal resistance (K·sec/J), and L is the upper platen. The thickness (mm), k is the thermal conductivity of the upper platen 40 (Wmm ^-1 K ^-1 ), and S is the area of the upper platen 40 (mm ² ).

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

Hereinafter, examples of the present invention will be described.

(Example of measurement data using direct evaluation method) In the double-sided grinding of the workpiece in the double-sided grinding device, the structure 220 shown in FIG. 4 is used to evaluate the rotation state of the workpiece.

The measurement results are shown in Figure 8 .

In Figure 8, the horizontal axis represents the grinding time, and the vertical axis represents the angular velocity difference Δω. Figure 8 shows the measurement results of two grinding processing batches (batch A and batch B). For processing batch A, the angular velocity difference Δω changes periodically. On the other hand, in processing batch B, the angular velocity difference Δω showed an almost constant value.

It can be seen from this that in process batch A, the workpiece continues to rotate freely as expected during the grinding process. On the other hand, in the processing batch B, it is understood that the workpiece has stopped.

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

(Example of mapping of indirect evaluation method) From the following sequence, a mapping that can be used for the above indirect evaluation method is constructed.

(1st mapping) First, the index A is determined according to the above formula (1) from the plate thickness deviation TTV of the glass substrate after double-sided grinding and the height data at each position shown in Figure 6.

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

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

The selected parameter is set to the temperature difference ΔT between the first temperature sensor and the second temperature sensor of the polishing pad on the pressure plate of the double-sided polishing device.

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

Next, a mapping is constructed from the relationship between the measurement results of the "selected parameters" obtained in the actual polishing process and the above-mentioned index A.

An example of the constructed mapping (hereinafter referred to as the "first mapping") is shown in FIG. 9 .

In the first map, the horizontal axis is the average 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 grinding steps, and the vertical axis is the index A value.

The first map depicts the combination of the index A and the temperature difference ΔT obtained from equation (1) for the glass substrates obtained from each polishing batch.

As can be seen from the first map, the drawing group is roughly divided into the first group on the upper side and the second group on the lower side. In addition, 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 -1.05 μm to -0.580 μm. This boundary line corresponds to the threshold Tv in the above equation (2).

In addition, the boundary X between the two groups of horizontal axes is the position where the temperature difference ΔT = -0.3°C.

It can be seen from the first map that when the temperature difference ΔT is lower than -0.3°C, the symmetry of the polished glass substrate decreases.

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

Regarding this, consider the following scenario.

As a main form of a glass substrate that obtains good symmetry, it is assumed that the thickness t 1 of the center O (point P ₁ ) of the glass substrate in Figure ₆ is greater than the thickness t of the remaining four surrounding points (P ₂ ~ P ₅ ). ₁ ~ t ₅ situation.

In this case, since TTV = (maximum value of thickness - minimum value of thickness), it becomes . Here, t _min is the minimum thickness among the four surrounding points (P ₂ ~ P ₅ ).

As mentioned above, because , so it 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 becomes a roughly wedge shape, with the center O as the midpoint, the thickness at one of the two ends is the largest (t _max ), and the thickness at the other end of the two ends is the smallest ( t _min ).

In this case, because , and |t ₁ -t _ave | is almost zero, so it becomes .

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

In addition, another main form of the glass substrate to obtain good symmetry, that is, the thickness t ₁ of the center O (point P ₁ ) of the glass substrate in Figure 6 is smaller than the remaining four surrounding points (P ₂ ~ P ₅ ) The same result can also be obtained when the thickness is t ₁ to t ₅ .

In this way, when index A is used, in the constructed mapping, the value of index A in the abnormal rotation area (group 2) is approximately twice the value of index A in the normal rotation area (group 1). tendency.

(2nd mapping) Next, the second map is constructed using the above equation (2).

The second mapping constructed is shown in Figure 10 .

In the second map, the horizontal axis represents the temperature difference ΔT as in the first map. On the other hand, the vertical axis represents the symmetry index value B represented by equation (2).

In addition, in the second map, the symmetry index value B is binarized and displayed as 1 and 0. Among them, "0" means that the symmetry index value B represented by the formula (2) is less than 0, and "1" means that the symmetry index value B represented by the formula (2) exceeds 0. In addition, the threshold Tv in equation (2) is set to -1.05 μm.

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

Therefore, by using the first map and/or the second map, it can be determined whether the rotation of the workpiece in the grinding step is normal.

Next, with reference to the second map, the results of double-sided grinding of the workpiece while monitoring the rotational state of the workpiece will be described.

(example 1) By the above-mentioned first method, a double-sided grinding device is used to double-side polish the tool.

The workpiece is a glass substrate with a diameter of 300 mm and a thickness of about 0.7 mm. In the rotation state determination step S120, an indirect evaluation method is used.

As shown in FIG. 3 above, in the first method, in the rotation state determination step S120, it is determined whether the rotation of the workpiece is abnormal. Also, in the indirect evaluation method, this judgment is performed by monitoring selected parameters.

The changing behavior of selected parameters in the grinding process is shown in Figure 11.

In Figure 11, the horizontal axis represents the grinding time, and the left vertical axis represents the selected parameter, that is, the temperature difference ΔT shown in Figure 10. In addition, in FIG. 11 , for reference, the temperature of the slurry supplied during polishing is shown on the right axis of the figure.

In Figure 11, the horizontal dotted line (ΔT=-0.3°C; hereinafter referred to as "reference line U") represents the basis for judging the rotation state of the workpiece. That is, when the temperature difference ΔT is lower than the reference line U, abnormality may occur in the rotation of the workpiece.

Among them, in Example 1, the temperature difference ΔT exceeds the reference line U throughout the entire grinding process. Therefore, in Example 1, in the rotation state determination step S120, the rotation of the workpiece is determined to be normal.

Furthermore, as a result, in Example 1, the polishing conditions are not changed in the rotation state determination step S120, and the first method proceeds to the polishing maintenance step S130. Subsequently, after the specified grinding time (10 minutes) has elapsed, the grinding completion judgment is performed in the grinding completion judgment step S150, and the grinding process is completed in the grinding completion step S150.

After the grinding process, the symmetry index value B of the obtained glass substrate was measured. As a result, the symmetry index value B=-0.195, indicating that the glass substrate has sufficient symmetry.

(Example 2) By the same method as Example 1, double-sided grinding of the workpiece is performed.

The changing behavior of selected parameters in the grinding process is shown in Figure 12 .

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

As shown in Figure 12, in Example 2, after about 1500 seconds, the temperature difference ΔT was monitored to be lower than the baseline U.

Therefore, in Example 2, at this time sequence, the rotation of the workpiece is determined to be abnormal. That is, the first method proceeds from the rotation state determination step S120 to the condition changing step S140, and changes the polishing conditions. In addition, in Example 2, the grinding conditions of the workpiece were changed by increasing the temperature of the supplied slurry (refer to the increase in slurry temperature in Figure 12).

As a result, the temperature difference ΔT exceeded the reference line U again, confirming that it had returned to the normal range. Subsequently, in the first method, after the designated grinding time (10 minutes) has passed, the grinding completion judgment is performed in the grinding completion judgment step S150, and the grinding process is completed in the grinding completion step S150.

After the grinding process, the symmetry index value B of the obtained glass substrate was measured. As a result, the symmetry index value B=-0.067, indicating that the glass substrate has sufficient symmetry.

In addition, in the double-sided grinding device used, the mass m of the upper platen 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 , the area S is 1.01×10 ⁶ mm ² , and the thickness L is 45 mm.

Therefore, the time constant τ of heat conduction in the upper platen 40 expressed by the above equation (3) is approximately 580 sec. In contrast, the time required for the cycle from the rotation state determination step S120 to the polishing completion determination step S150, that is, the sensing period In in FIG. 3 is 2 minutes or less. Therefore, the sensing period In is sufficiently smaller than the time constant τ.

(Example 3) By the same method as Example 1, double-sided grinding of the workpiece is performed.

The changing behavior of selected parameters in the grinding process is shown in Figure 13.

In Figure 13, the horizontal axis represents the grinding time, and the left vertical axis represents the selected parameter, that is, the temperature difference ΔT. In addition, in FIG. 13 , for reference, the temperature of the slurry supplied during grinding is shown on the right axis of the figure.

As shown in FIG. 13 , in Example 3, about 2200 seconds after the start of polishing, the temperature difference ΔT was monitored to be lower than the reference line U.

Therefore, in Example 3, at this time sequence, the rotation of the workpiece is determined to be abnormal. That is, the first method proceeds from the rotation state determination step S120 to the condition changing step S140, and changes the polishing conditions. In addition, in Example 3, the grinding conditions of the workpiece were changed by increasing the temperature of the supplied slurry (refer to the increase in the slurry temperature after 2200 seconds in Figure 13).

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

Subsequently, approximately 4200 seconds after the start of grinding, the temperature difference ΔT was monitored to be lower than the reference line U again.

Therefore, in Example 3, at this time sequence, the rotation of the workpiece was determined to be abnormal, and the polishing conditions were changed again. In addition, here, by increasing the temperature of the supplied slurry, the polishing conditions of the workpiece are changed (refer to the increase in the slurry temperature after 4000 seconds in Figure 13).

In the first method, after the specified grinding time (90 minutes) has elapsed, the grinding completion is judged in the grinding completion judgment step S150, and the grinding process is completed in the grinding completion step S150.

After the grinding 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 obtained sufficient symmetry.

In addition, in Example 3, the sensing period In is 2 minutes or less. Therefore, the sensing period In is sufficiently smaller than the time constant τ.

(Example 4) Using the previous method, the workpiece is ground on both sides. The double-sided grinding device used and the shape of the workpiece are the same as in Example 1.

The changing behavior of selected parameters in the grinding process is shown in Figure 14.

In Figure 14, the horizontal axis represents the grinding time, and the left vertical axis represents the selected parameter, that is, the temperature difference ΔT. In addition, in FIG. 14 , for reference, the temperature of the slurry supplied during grinding is shown on the right axis of the figure.

As shown in FIG. 14 , in Example 4, about 2600 seconds after the start of polishing, the temperature difference ΔT was monitored to be lower than the reference line U.

However, in this Example 4, as before, the workpiece was polished to the end with the initially set polishing conditions.

After the grinding process, the symmetry index value B of the obtained glass substrate was measured. As a result, it can be seen that the symmetry index value B=-1.301 indicates that the symmetry of the glass substrate is poor.

In this way, by using the first method to double-side polish the workpiece, it was confirmed that a glass substrate with small thickness variation was obtained.

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

However, this is only an example. In the condition changing step S140, the grinding conditions can also be changed by changing another control factor. For example, the grinding conditions can be changed according to the rotation speed of the upper and lower platens, the temperatures of the upper and lower platens, the loads of the upper and lower platens, and the supply amount of slurry.

Figures 15 to 17 show an example of the control factors that affect the selected parameter (ie, the temperature change ΔT mentioned above).

Figure 15 shows the relationship between the rotation speed of the lower platen and the temperature change ΔT. Figure 16 shows the relationship between the load on the upper platen and the temperature change ΔT. In addition, the relationship between the slurry supply amount and the temperature change ΔT is shown in FIG. 17 .

It can be said from these figures that at least the value of the selected parameter can be increased or decreased by changing the rotation speed of the lower platen, the load of the upper platen, 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 content of this Japanese application is incorporated by reference into this application.

10: Double-sided grinding device 20: Base 30: Lower pressure plate 32: Sun gear 33: Internal gear 40: Upper pressure plate 50: Lifting mechanism 52: Cylinder device for lifting 54: Piston rod 55: Universal joint 60: Rotation transmission mechanism 61: Motor drive shaft 62: Joint portion 62a: Keyway 70: Frame 72: Beam 80: Suspension member 80a: Suspension 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 A: Index A: Processing batch B: Symmetry Index value B: Processing batch d: Distance In: Sensing period O: Center P ₁ to P ₅ : Point S100: First method S110: Step S120: Step S130: Step S140: Step S150: Step S160: Step t: Time U: Baseline X: Value ΔT: Temperature difference Δω: Angular velocity difference

FIG. 1 is a diagram schematically showing a longitudinal section of the double-sided polishing device. FIG. 2 is a top view schematically showing a state in which a carrier is arranged on a polishing pad under a pressure plate of a double-sided polishing device. FIG. 3 is a diagram schematically showing the flow of a method for double-sided grinding of a workpiece according to an embodiment of the present invention. FIG. 4 is a diagram schematically showing an example of a structure used when evaluating the rotation speed of a workpiece using a direct evaluation method in a method for double-side grinding a workpiece according to an embodiment of the present invention. FIG. 5 is a graph schematically showing the relationship between the polishing time and the angular velocity difference Δω that can be measured when using the configuration shown in FIG. 4 . FIG. 6 is a diagram showing points P ₁ to P ₅ on the surface of the polished glass substrate. FIG. 7 is a diagram schematically showing an example of the mapping constructed by the indirect evaluation method in the method of double-sided grinding of a workpiece according to one embodiment of the present invention. FIG. 8 is a graph showing the time change of the angular velocity difference Δω measured in two grinding treatment batches. FIG. 9 is a diagram showing an example of a mapping constructed from the relationship between the temperature difference ΔT measured by two temperature sensors and the index A. FIG. 10 is a diagram showing an example of a map constructed from the relationship between the temperature difference ΔT measured by two temperature sensors and the symmetry index value B. FIG. 11 is a graph showing the changing behavior of a selected parameter (temperature difference ΔT) in the grinding process of Example 1. FIG. 12 is a graph showing the changing behavior of a selected parameter (temperature difference ΔT) in the grinding process of Example 2. FIG. 13 is a graph showing the changing behavior of a selected parameter (temperature difference ΔT) in the grinding process of Example 3. FIG. 14 is a graph showing the changing behavior of a selected parameter (temperature difference ΔT) in the grinding process of Example 4. FIG. 15 is a graph showing an example of the relationship between the rotation speed of the lower platen and the selected parameter (temperature difference ΔT). Figure 16 is a graph showing an example of the relationship between the load of the upper platen and the selected parameter (temperature difference ΔT). FIG. 17 is a graph showing an example of the relationship between the supply amount of slurry and the selected parameter (temperature difference ΔT).

In: sensing cycle

S100: 1st method

S110: Steps

S120: Steps

S130: Steps

S140: Steps

S150: Steps

S160: Steps

Claims (9)

A method, which is double-sided grinding of a workpiece made of a glass substrate; and has the following steps: (1) Start grinding the workpiece; (2) Real-time monitoring of the rotation status of the above workpiece; and (3) In the step of (2) above, when it is determined that the rotation state of the workpiece deviates from the specified state, the polishing conditions are changed. The method of claim 1, wherein the method is implemented by a double-sided grinding device having an upper platen, a lower platen, and a supply mechanism for supplying slurry between the two; and In the above step (3), the rotation speed of the upper platen and the lower platen of the double-sided grinding device, the temperature of the upper platen and the lower platen, the upper platen and the lower pressure are changed. At least one of the group consisting of the load of the disk, the supply amount and the temperature of the above-mentioned slurry. The method of claim 1 or 2, wherein in the above step (2), the above-mentioned rotational state of the above-mentioned workpiece is directly measured. The method of claim 2, wherein in the step (2), the rotational state of the workpiece is predicted from the measurement value of the sensor provided in the double-sided grinding device. Such as the method of request item 4, where The above step (2) has the following steps: (i) Determine indicators indicating the state of the polished glass substrate; (ii) Construct a mapping representing the relationship between the measurement results of the above-mentioned sensors and the indicators determined in (i) above; and (iii) Refer to the map constructed above and determine from the measurement results of the sensor whether it is in a region indicating that the rotation state of the workpiece is abnormal. The method of claim 5, wherein the above-mentioned index is an index indicating the symmetry of the above-mentioned ground glass substrate. The method of claim 6, wherein the sensor is one or more temperature sensors provided on the upper platen and/or the lower platen of the double-sided grinding device. For example, the method of claim 1 or 2 further has the following steps: (4) After the above step (3), when it is determined that the rotation state of the workpiece deviates from the designated state, the polishing conditions after the above change are further changed. The method of claim 8, wherein the sensing period In of the above-mentioned step (3) and/or the above-mentioned step (4) does not reach the time constant τ of the platen on the double-sided grinding device represented by the following formula; Here, m is the mass of the upper platen (kg), c is the specific heat of the upper platen (Jkg ^-1 K ^-1 ), L is the thickness of the upper platen (mm), and k is the upper platen. The thermal conductivity (Wmm ^-1 K ^-1 ), S is the area of the above upper platen (mm ² ).