TWI740606B - Double side polishing method for workpiece - Google Patents

Abstract

The present invention aims at providing a double side polishing method for a workpiece, which method is capable of intentionally controlling the outer peripheral shape of the workpiece. The double side polishing method for a workpiece of the present invention, wherein a workpiece is held in a holding hole by a carrier plate which has more than one holding hole that holds the workpiece to double side polish the workpiece, includes：a step of acquiring the relationship between the inner peripheral diameter of the holding hole and the edge roll-off quantity of the workpiece, a step of deciding the inner peripheral diameter of the holding hole, on the basis of an expected edge roll-off quantity and the acquired relationship between the inner peripheral diameter of the holding hole and the edge roll-off quantity of the workpiece, and a step of double side polishing the workpiece, by using the carrier plate having the holding hole with the decided inner peripheral diameter.

Description

Two-sided grinding method of workpiece

The invention relates to a method for grinding both sides of a workpiece.

In the manufacture of semiconductor wafers such as silicon wafers, which are typical examples of workpieces for polishing, in order to obtain higher-precision wafer flatness quality and surface roughness quality, a two-sided polishing step (such as , Patent Document 1). [Advanced Technical Literature] [Patent Literature]

[Patent Document 1] International Publication No. 2014-2467

[The problem to be solved by the invention]

However, it is required to control the shape of the wafer according to its application. For example, in the case of epitaxial growth, especially when growing an epitaxial layer with a thickness of 4 μm (micrometer) or more, it is sometimes better to lower the wafer intentionally. Peripheral.

In such a case, for example, double-sided polishing is performed by using a polishing pad with low hardness, and it is considered that the outer periphery of the wafer is intentionally lowered based on the elastic deformation of the polishing pad.

However, when a low-hardness polishing pad is used, there may be problems such as a decrease in the flatness (for example, GBIR) of the entire wafer. Therefore, other methods that can intentionally control the shape of the outer periphery of the wafer are required. Therefore, such problems generally occur not only in wafers, but also in workpieces provided for double-sided polishing.

The object of the present invention is to provide a double-sided grinding method of a workpiece, which can intentionally control the outer peripheral shape of the workpiece. [Means to solve the problem]

The essential structure of the present invention is as follows: The grinding method of the workpiece of the present invention is a double-sided grinding method of the workpiece. A carrier plate having one or more support holes for supporting the workpiece supports the workpiece in the support hole, and performs double-sided grinding of the workpiece. The characteristics of the method are It includes: The step of obtaining the relationship between the inner circumference of the support hole and the edge roll-off amount of the workpiece; The step of determining the inner circumference of the support hole according to the expected edge roll-off amount and the obtained relationship between the inner circumference of the support hole and the edge roll-off amount of the workpiece; and The step of polishing both sides of the workpiece is performed using the transport plate having the support hole with the determined inner circumferential diameter.

Here, the so-called "roll-off" means that the outer circumference of the workpiece sags and the thickness of the outer circumference decreases. The so-called "descent amount" refers to the amount of sagging of the outer circumference of the workpiece. The greater the amount of edge drop, the greater the sagging of the outer circumference of the workpiece, which means that the thickness of the outer circumference is thinner.

As an indicator of the "edge reduction amount", for example, ESFQR can be used. The so-called "ESFQR" is an index indicating the flatness of the wafer as specified in the SEMI specification. It refers to the sector formed in the peripheral area of the wafer (30mm (millimeter) from the outer periphery of the wafer is divided into 72 equal parts in the circumferential direction). The thickness of the wafer is calculated by calculating the absolute value of the maximum displacement of the reference plane obtained by the least square method. "ESFQRmax" is the maximum value. However, when the workpiece is a wafer, because the outer edge may be chamfered, for example, an area 1 mm in the radial direction from the outer periphery can be excluded as the exclusion area. For wafers with a lowered outer periphery, the larger the "ESFQR", the greater the "descent amount".

In addition, the "inner peripheral diameter" refers to the inner peripheral diameter of the aforementioned insert when the inner peripheral surface (for example, made of resin) of the support hole has an insert.

Here, the above-mentioned edge drop amount is preferably an edge drop amount in a state of a fixed size. The so-called "fixed size state" refers to the state where the workpiece is polished on both sides until the thickness of the workpiece is the same as the thickness of the conveying plate.

Generally, in double-sided polishing, since an elastomeric polishing pad is used to simultaneously polish the front and back of the workpiece, as shown in states A to C in FIG. 5, the workpiece (shown as a wafer in FIG. 5) is polished. That is, as shown in FIG. 5, in the initial stage of polishing (state A), the overall shape of the workpiece is an upward convex shape, a large drooping shape is also seen on the outer periphery of the workpiece, and the amount of edge drop becomes large. At this time, the thickness of the workpiece is sufficiently thicker than the thickness of the conveying plate. During polishing (state B), the overall shape of the workpiece becomes a substantially flat shape, and the amount of edge drop of the outer periphery of the wafer becomes small. At this time, the thickness of the workpiece is approximately equal to the thickness of the conveying plate. After that, when polishing is performed (state C), the shape of the workpiece gradually becomes a concave shape in the center portion, and the outer periphery of the workpiece becomes a raised shape. In state C, the thickness of the conveying plate becomes thicker than the thickness of the workpiece. The above state B is a fixed size state.

In addition, it is preferable that the inner circumferential diameter determined as described above is 1 mm to 5 mm larger than the diameter of the workpiece.

In addition, the above-mentioned double-sided polishing was performed using a polishing pad. The surface hardness (ASKER C) of the above-mentioned polishing pad is preferably 70-90. Here, "the surface hardness of the polishing pad (ASKER C)" is measured with the ASKER C hardness meter.

In addition, the above-mentioned workpiece is preferably a silicon wafer.

Furthermore, it further includes a step of obtaining the relationship between the inner circumference of the support hole and the surface roughness of the end surface of the workpiece; In the step of determining the inner circumference of the support hole, the inner circumference of the support hole is preferably determined based on the expected surface roughness of the workpiece end surface and the obtained relationship between the inner circumference of the support hole and the surface roughness of the workpiece end surface. [Effects of the invention]

According to the present invention, it is possible to provide a double-sided grinding method of a workpiece, and it is possible to intentionally control the outer peripheral shape of the workpiece.

Hereinafter, the embodiments of the present invention will be illustrated in detail with reference to the drawings.

＜Double-sided grinding device of workpiece＞ Fig. 1 is a schematic diagram of an example of a double-sided polishing apparatus used in a double-sided polishing method of a workpiece according to an embodiment of the present invention.

The double-sided polishing device 100 can have the same configuration as a double-sided polishing device generally used for double-sided polishing of a workpiece (wafer W), except that the inner circumference of the support hole 1 is determined by the method described later. Hereinafter, an example will be described.

As shown in FIG. 1, the double-sided polishing apparatus 100 for a workpiece of this embodiment has one or more (one in the example of the figure) conveying plate 2, and the conveying plate 2 has a supporting workpiece (the present embodiment is a wafer W (for example, Silicon wafer)) one or more (1 in the example of the figure) support hole 1. As shown in FIG. 1, the double-sided grinding device 100 of this example includes: a rotating platform 3 having an upper platform 3a and a lower platform 3b opposed thereto; a sun gear 4 provided at the center of rotation of the rotating platform 3; and an internal gear 5. The ring is arranged on the outer periphery of the rotating platform 3. As shown in FIG. 1, the opposite surfaces of the upper and lower rotating platforms 3, namely the lower side of the polishing surface of the upper platform 3a and the upper side of the polishing surface of the lower platform 3b, are respectively pasted with polishing pads 6.

Moreover, as shown in Fig. 1, the conveying plate 2 is designed between the upper platform 3a and the lower platform 3b. In addition, in the example shown in the figure, the double-sided polishing device 100 has only one conveying plate 2, but plural conveying plates 2 may be provided, and the number of support holes 1 may be one or more, or two or more. In the example shown in the figure, the workpiece (wafer W) is supported in the supporting hole 1. In this example, the diameter of the workpiece (wafer W) provided for polishing by the double-sided polishing apparatus 100 is 300 mm, but it is not limited to this case. In addition, when the workpiece is the wafer W, the crystal orientation, conductivity type, and the like are not particularly limited.

Here, the double-face grinding device 100 is a planetary gear type double-face grinding device capable of planetary movement of the transport plate 2 by rotating the sun gear 4 and the internal gear 5 to revolve and rotate. That is, while supplying the polishing liquid, the conveying plate 2 is moved planetary, and the upper platform 3a and the lower platform 3b are rotated relative to the conveying plate 2 at the same time, and the polishing pad 6 attached to the upper and lower rotating platform 3 and the conveying plate 2 are supported by sliding Both sides of the workpiece (wafer W) supported in the hole 1 can be polished at the same time.

Here, in this embodiment, the surface hardness (ASKER C) of the polishing pad 6 is preferably 70 to 90.

In addition, the inner peripheral surface of the conveying plate 2 may or may not include an insert (for example, made of resin).

As described later, the inner circumference of the support hole 1 of the conveying plate 2 is determined through a predetermined step, but the inner circumference is preferably 1 mm to 5 mm larger than the diameter of the workpiece. In this example, because the workpiece is a wafer with a diameter of 300 mm, the inner circumference of the support hole 1 of the transport plate 2 is preferably 301 to 305 mm.

＜Method of grinding both sides of workpiece＞ Fig. 2 is a flowchart of a method for polishing both sides of a workpiece according to an embodiment of the present invention. As shown in FIG. 2, in the method for polishing both sides of a workpiece according to this embodiment, first, the relationship between the inner circumference of the support hole 1 and the amount of edge drop of the workpiece (wafer W) is obtained (step S101: first step).

Here, the relationship between the inner circumferential diameter of the support hole 1 and the amount of edge drop of the workpiece (wafer W) will be described in detail. Figure 3 is a diagram showing the relationship between the inner circumference of the support hole of the conveying plate and ESFQRmax. Also, as mentioned above, ESFQR is one of the index of edge reduction. The ESFQR in Fig. 3 represents the ESFQR in the fixed size state. The details of the experiment in FIG. 3 will be described in the Examples later.

As a result of intensive research in order to solve the above-mentioned problem, the inventors found that as the inner circumference of the support hole of the conveying plate increases, as shown in FIG. 3, the edge drop amount (ESFQRmax in FIG. 3) increases. Here, in the initial stage of polishing (state A in FIG. 5), since the thickness of the wafer is thicker than the thickness of the transport plate, the outer periphery of the wafer is directly polished with an elastic polishing pad. When polishing is carried out from there, and the thickness of the wafer becomes the same as the thickness of the transport plate, the outer periphery of the wafer is protected by the transport plate, the effect of the polishing pad on the outer periphery of the wafer is reduced, and the polishing amount of the center of the wafer is relatively increased. , The wafer becomes flat (state B), and then, when the thickness of the wafer becomes thinner than the thickness of the transport plate, the outer periphery of the wafer is protected by the transport plate, and the polishing of the center of the wafer progresses, and the center of the wafer becomes Depressed shape (state C). It can be seen that when the gap between the inner peripheral surface of the support hole and the workpiece (wafer W) becomes larger, the outer peripheral portion of the wafer is protected by the transport plate, and the effect of reducing the amount of grinding of the outer peripheral portion becomes smaller. In addition, the inner peripheral diameter of the support hole The larger the amount, the more the amount of polishing liquid is introduced, and the penetration polishing rate and the etching force increase due to the promotion of polishing and the like. As the inner circumference of the support hole of the conveying plate increases, the amount of edge drop is considered to increase.

In this way, the inner circumference of the support hole 1 has a correlation with the amount of edge drop of the workpiece (wafer W). Specifically, as described above, there is a relationship that the amount of edge drop increases as the inner diameter of the support hole of the transport plate increases. Therefore, in step S101 (the first step), when polishing the workpiece (wafer W) on both sides (for example, when polishing to a fixed size state), the inner circumference of the support hole 1 and the current workpiece (wafer W) By preparing sufficient data in advance, the inner circumference of the support hole 1 and the edge of the workpiece (wafer W) can be obtained numerically based on the data itself or statistical processing of the data or other data. The relationship between the amount of descent, etc., is the relationship between the inner circumference of the support hole and the amount of descent of the workpiece edge. For example, the relationship between the inner circumference of the support hole and the amount of lowering of the workpiece edge may be stored in a computer with a memory unit (memory, etc.), or a computer with a communication unit or the like may send and receive information related to the above relationship. The above information can be updated in real time or in due course.

Next, as shown in FIG. 2, in this embodiment, the inner circumference of the support hole is determined based on the expected edge drop amount and the obtained relationship between the support hole inner diameter and the workpiece edge drop amount (step S102: second step ). As described above, the inner circumference of the support hole 1 has a correlation with the amount of edge drop of the workpiece (wafer W). Specifically, there is a relationship that the amount of edge drop becomes larger as the inner circumference of the support plate of the conveying plate increases. Step S101 ( In the first step), the relationship is obtained. Therefore, it is possible to determine the inner circumference of the support hole of the conveying plate used in double-sided grinding by determining the expected amount of edge drop, and using the obtained relationship between the inner circumference of the support hole and the amount of drop of the workpiece edge. For example, if the relationship between the inner circumference of the support hole and the amount of edge drop is obtained (for example, linearly), as the relationship between the inner diameter of the support hole and the amount of edge drop of the workpiece in step S101 (first step), Substituting the expected edge drop amount into the above equation, the inner circumferential diameter of the support hole of the conveying plate used for double-sided polishing can be obtained. It is not particularly limited, but because the inner circumference of the conveying plate is often an integer value, the integer value can also be obtained by rounding or the like. Or, the relationship between the inner circumference of the support hole and the amount of lowering of the edge of the workpiece can be used in this way. Using the support hole data of the conveying plate that can achieve the expected amount of edge lowering (and the amount of edge lowering close to it), both sides can be determined The inner diameter of the support hole of the conveying plate used for polishing. For example, it is possible to calculate the average value of the support hole data of the conveying plate that can achieve the expected edge drop amount (and the edge drop amount close to it). Similarly, it is not particularly limited, but because the inner circumferential diameter of the conveying plate is often an integer value, the integer value can also be obtained by rounding or the like. Alternatively, it is also possible to determine the inner circumference of the support hole of the conveying plate that can achieve the maximum number of the expected edge drop amount (and the amount of edge drop close to it) as the inner circumference of the support hole of the conveying plate used for double-sided polishing. It is also possible to perform statistical processing on the above-mentioned data as a result of the relationship between the inner circumference of the support hole and the amount of descent of the workpiece edge. For example, the above-mentioned decision can be carried out by a computer with a calculator.

Next, as shown in FIG. 2, in this embodiment, the double-sided polishing of the workpiece (wafer W) is performed using a conveying plate having a support hole having a determined inner circumferential diameter (step S103: third step). The double-sided polishing in step S103 (the third step) can be performed, for example, using the double-sided polishing apparatus 100 described with reference to FIG. 1. At this time, it is better to replace the conveying plate of the double-sided grinding device with a conveying plate with a determined inner circumferential diameter support hole, but it is also possible to prepare a double-sided grinding device with a conveying plate with a determined inner circumferential diameter support hole. The double-sided grinding can be carried out in the usual way. For example, as mentioned above, while supplying the polishing liquid, the conveying plate 2 is moved planetarily, and at the same time, by rotating the upper platform 3a and the lower platform 3b relative to the conveying plate 2, the polishing pad 6 and the conveying plate attached to the upper and lower rotating platform 3 are slid 2 Both sides of the workpiece (wafer W) supported in the support hole 1 can be polished simultaneously on both sides of the workpiece (wafer W). Hereinafter, the double-sided polishing method of the workpiece of this embodiment will be described.

According to the double-sided polishing method of the workpiece according to this embodiment, it is possible to intentionally control the workpiece (wafer W ) Of the outer peripheral shape. In other words, the determined inner circumferential diameter of the support hole intentionally controls the outer circumferential shape of the workpiece (wafer W) in order to correspond to the expected edge drop amount. According to the double-sided polishing method of a workpiece according to this embodiment, as the polishing pad, a polishing pad with a surface hardness (ASKER C) of 70 to 90 is used. Compared with the case of replacing a polishing pad with a low hardness, there is no loss of material exchange. In addition, there is no problem that the overall flatness (GBIR, etc.) of the workpiece (wafer W) is reduced due to the use of a low-hardness polishing pad. Also, according to the double-sided polishing method of the workpiece according to this embodiment, the contact area between the workpiece (wafer W) and the inner peripheral surface of the support hole of the conveying plate is reduced, because the rotation of the workpiece (wafer W) is promoted, and it is also implemented as described later. As shown in the example, reducing the roughness of the end surface of the workpiece (wafer W) can also improve the surface quality of the end surface.

Here, the edge drop amount (the workpiece edge drop amount in step S101 and the expected edge drop amount in step S102) is preferably the edge drop amount in a fixed size state. The reason is that, in order to obtain the expected edge drop amount, compared to the case where polishing is performed from a fixed size state, there is no adverse effect on the overall flatness of the workpiece. On the other hand, even in the state before the fixed size state (state A in FIG. 5), a greater amount of edge drop (amount of sag) can be obtained.

In addition, the determined inner circumferential diameter is preferably 1 mm to 5 mm larger than the diameter of the workpiece. The reason is that by determining a range where the inner circumference is larger than the workpiece diameter by 1 mm or more, the gap between the inner circumference of the support hole and the workpiece (wafer W) increases more reliably, and the outer circumference is protected by the transport plate. The effect is weakened and the amount of grinding fluid is increased. On the other hand, by determining the range where the inner circumference of the support hole is greater than the diameter of the workpiece by 5mm or less, the workpiece can be supported in the support hole more reliably. Also, it is not particularly limited, but since the diameter of the workpiece and the inner circumference of the workpiece support hole of the conveying plate are always integer values, it is preferable that the determined inner circumference be an integer value within the above-mentioned range. For example, when the diameter of the workpiece is 300 mm, the inner circumference of the workpiece support hole of the conveying plate is preferably one of 301 mm, 302 mm, 303 mm, 304 mm, or 305 mm.

In addition, double-sided polishing is performed using a polishing pad, and the surface hardness (ASKER C) of the polishing pad is preferably 70 to 90. The reason is that compared with the case of replacing with a low-hardness polishing pad, there is no loss of material exchange, and there is no overall flatness of the workpiece (wafer W) caused by the use of a low-hardness polishing pad (GBIR, etc.) The problem of falling.

In addition, when the double-sided polishing in step S103 (the third step) is completed, it is preferable to measure the amount of descent of the outer peripheral portion of the workpiece (for example, ESFQR). In this way, the above-mentioned results are fed back, the data can be updated, and the accuracy of obtaining the expected edge drop amount when the double-sided polishing is started next time can be improved.

Here, it further includes the step of obtaining the relationship between the inner circumference of the support hole and the surface roughness of the end surface of the workpiece. In the step of determining the inner circumference of the support hole, the inner circumference of the support hole is preferably based on the expected surface roughness of the end surface of the workpiece and The obtained relationship between the inner circumference of the support hole and the surface roughness of the end surface of the workpiece is determined. As shown in Fig. 4 described later, because the inner diameter of the workpiece support hole with the conveying plate is larger, the surface roughness Ra of the workpiece end surface after grinding is smaller. In view of the expected edge drop amount and the expected workpiece The surface roughness of the end surface determines the appropriate inner circumference of the workpiece support hole of the conveying plate, and the outer peripheral shape of the workpiece and the surface roughness of the end surface of the workpiece can be intentionally controlled at the same time.

Above, the embodiments of the present invention have been described, but the present invention is not limited by the above-mentioned embodiments at all. For example, the amount of edge drop in the outer peripheral portion is not limited to the case where ESFQR is used as an index. Hereinafter, examples of the present invention will be described, but the present invention is not limited by the following examples at all. [Example]

Prepare transport plates (inner diameters of 301 mm, 302 mm, 303 mm, 304 mm, and 305 mm) with different inner diameters of the support holes of the workpiece. For a wafer with a diameter of 300 mm, use the double-side polishing device shown in FIG. 1 to perform double-side polishing. After performing double-sided polishing, the area 1 mm from the outer periphery of the wafer in the radial direction is regarded as the ESFQR except for the edge exclusion area, and the flatness measuring device (manufactured by KLA Tencor: Wafersight2) is used to measure the maximum value (ESFQRmax). Figure 3 and Table 1 show the measurement results. As a result, it is understood that the larger the inner circumference, the larger the ESFQRmax, and the edge reduction can be achieved.

[Table 1] The inner circumference of the support hole Number of samples Average (nm) Standard deviation (nm) 301mm 10 41.6 5.4 302mm 10 45.4 3.9 303mm 10 47.4 5.1 304mm 10 55.6 7.0 305mm 10 62.3 2.9

As shown in Figure 3 and Table 1, it is understood that the inner circumference of the support hole of the workpiece is related to the amount of edge drop of the wafer. Specifically, as the inner diameter of the workpiece support hole of the conveying plate increases, the amount of edge drop becomes larger. Relationship. Therefore, by obtaining this relationship, the inner circumference of the support hole of the workpiece can be determined based on the expected edge drop amount and the obtained relationship.

Secondly, the MPS of Chapman was used to measure the roughness Ra of the wafer end surface after both sides were polished. Figure 4 and Table 2 show the measurement results.

[Table 2] The inner circumference of the support hole Number of samples Average (Å) Standard deviation (Å) 301mm 20 43.7 12.5 302mm 20 24.0 12.2 303mm 20 20.7 4.2 304mm 20 18.2 4.7 305mm 20 15.4 2.7

As shown in Fig. 4 and Table 2, it is understood that by using a conveying plate with a large inner circumference of the support hole of the workpiece, the surface roughness Ra is reduced and the surface quality is improved.

1: Support hole 2: Conveyor board 3: Rotating platform 3a: Go to the platform 3b: Lower platform 4: Sun gear 5: Internal gear 6: Grinding pad 100: Two-sided grinding device W: Wafer

[Figure 1] is a schematic diagram of an example of a double-sided polishing device used in a method for polishing both sides of a workpiece according to an embodiment of the present invention; [Fig. 2] is a flowchart of a method for grinding both sides of a workpiece according to an embodiment of the present invention; [Figure 3] A diagram showing the relationship between the inner circumference of the support hole of the conveying plate and ESFQRmax; [Figure 4] The relationship diagram between the inner circumference of the support hole of the conveying plate and the surface roughness Ra of the workpiece end surface; and [Fig. 5] is a diagram for explaining the fixed size state.

S101: Obtain the relationship between the inner circumference of the support hole and the amount of edge drop of the workpiece (wafer W)

S102: Determine the inner circumference of the support hole according to the expected amount of edge drop and the obtained relationship

S103: Use a transport plate with a support hole with a determined inner circumference to grind both sides of the workpiece (wafer W)

Claims (10)

A method for grinding both sides of a workpiece, wherein a carrier plate having one or more support holes for supporting the workpiece supports the workpiece in the support hole, and performing double-sided grinding of the workpiece, characterized by comprising: obtaining the support The steps of the relationship between the inner circumference of the hole and the edge roll-off amount of the workpiece; according to the expected edge roll-off amount and the obtained inner circumference of the support hole and the edge of the workpiece The relationship between the amount of edge roll-off is the step of determining the inner circumference of the support hole; and the step of grinding the workpiece on both sides using the transport plate having the support hole with the determined inner circumference. The double-sided grinding method of a workpiece according to claim 1, wherein the amount of edge drop is the amount of edge drop in a fixed size state, wherein the fixed size state is until the thickness of the workpiece is the same as the thickness of the conveying plate, and the workpiece The state of being polished on both sides. Such as the double-sided grinding method of the workpiece in claim 1, wherein the inner circumference diameter determined above is 1mm~5mm larger than the diameter of the workpiece. Such as the double-sided grinding method of the workpiece in claim 2, wherein the inner circumference diameter determined above is 1mm~5mm larger than the diameter of the workpiece. According to the method for polishing both sides of a workpiece according to any one of claims 1 to 4, wherein the above-mentioned two-side polishing is performed using a polishing pad; the surface hardness (ASKER C) of the above-mentioned polishing pad is 70-90. The method for grinding both sides of a workpiece according to any one of claims 1 to 4, wherein the workpiece is a silicon wafer. Such as the double-sided grinding method of the workpiece in claim 5, wherein the workpiece is a silicon wafer. For example, the double-sided grinding method of the workpiece according to any one of claims 1 to 4, further comprising: obtaining the relationship between the inner circumference of the support hole and the surface roughness of the end surface of the workpiece; wherein the above determines the inner circumference of the support hole In the diameter step, the inner circumference of the support hole is determined according to the expected surface roughness of the workpiece end surface and the obtained relationship between the inner circumference of the support hole and the surface roughness of the workpiece end surface. For example, the double-sided grinding method of the workpiece according to claim 8, wherein the double-sided grinding is performed using a grinding pad; the surface hardness (ASKER C) of the grinding pad is 70-90. Such as the double-sided grinding method of the workpiece in claim 8, wherein the workpiece is a silicon wafer.

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