TW201733737A - A double-side polishing method for wafer - Google Patents

Abstract

To provide a double-side polishing method for wafer capable of obtaining excellent flatness in overall shape of a wafer, as well as sufficiently suppressing edge roll off on the wafer. A double-side polishing method for wafer uses a donut-shaped upper plate and a donut-shaped lower plate to press and hold a wafer, supplies slurry to the wafer through a slurry supplying hole while rotating the upper plate and lower plate to polish both sides of the wafer, wherein a central hole is positioned in a central part of the upper plate and the lower plate, respectively, and polishing cloth is attached to a polishing surface of the upper plate and the lower plate, respectively. At least one of an outer compressed part and an inner compressed part is positioned on both of the polishing cloth attached to the upper plate and the lower plate, wherein the outer compressed part and the inner compressed part are formed by pressing an outer part or an inner part of the polishing cloth in a vertical direction using a polishing cloth compression tool, and a compression width A conforms with 0.05*D ≤ A, a compression width B conforms with 0.30*D ≥ B, wherein A denotes the compression width A is width of the outer compressed part in the horizontal direction, B denotes the compression width B is width of the inner compressed part in the horizontal direction, D denotes diameter of the wafer.

Description

Wafer two-side grinding method

The present invention relates to a two-side polishing method for simultaneously polishing the front and back surfaces of a wafer, and more particularly to a two-side polishing method for a wafer, which is capable of achieving good flatness in the overall shape of the wafer and capable of sufficiently suppressing the periphery of the wafer. Tired.

For example, in the manufacturing process of a semiconductor wafer such as a germanium wafer obtained by slicing a single crystal, it is possible to simultaneously polish both sides of the front and back sides of the wafer for the purpose of flattening the wafer shape or improving the surface roughness. Grinding.

In general, the two-side grinding is to press the wafer with the upper and lower fixed plates to which the polishing cloth is attached, to supply the slurry to the wafer, and to simultaneously drive the upper and lower fixed disks while grinding the wafer. The method on the back of the watch. Fig. 12 is a view showing the shape of the wafer as a function of time in the general double-sided polishing process when the polishing time passes in the order of Fig. 12(a) to Fig. 12(e). Picture. Further, in Fig. 12, the relationship between the wafer thickness and the thickness of the carrier sheet at each time point in Figs. 12(a) to 12(e) is also shown. In Figs. 12(a) to 12(e), the vertical axis represents the thickness of the wafer, and the horizontal axis represents the position from the center of the wafer when the radius of the wafer is R. That is, these figures show the shape of the cross-sectional shape of each wafer in the vertical direction by the thickness of each position from the center of the wafer, and the right enlarged view is an enlarged view of one end of the outer periphery (edge portion) of the wafer.

As shown in Fig. 12, in the double-side grinding, the front and back surfaces of the wafer are simultaneously polished by the polishing cloth attached to the upper and lower fixed plates, and the shape changes as shown in Fig. 12(a) as the polishing time elapses. ~ Figure 12 (e). In the initial stage of the polishing process shown in Fig. 12(a), the overall shape of the wafer (global shape) has a convex shape with a large thickness near the center, and a large roll off is also observed on the outer periphery of the wafer. . In addition, in this initial stage, the thickness of the wafer is much thicker than the thickness of the carrier sheet. In the next stage of Fig. 12(b), the overall shape of the wafer becomes a slightly flatter shape than the above-described convex shape, but the residual of the wafer periphery observed in the initial stage remains. When the polishing is performed again, the thickness of the wafer and the thickness of the carrier sheet are almost equal when the stage of Fig. 12(c) is reached, and the overall shape of the wafer becomes an approximately flat shape. Further, when the polishing cloth is an elastic body and is subjected to a certain pressure for polishing, especially in the stage of Fig. 12 (a) and Fig. 12 (b), the polishing cloth sinks by a certain amount at the time of polishing, thus The stress on the periphery of the wafer is greater than near the center. On the other hand, when the thickness of the wafer and the thickness of the carrier sheet become almost equal, the stress applied from the abrasive cloth to the periphery of the wafer is dispersed to the carrier sheet, so that the stress is lowered. Therefore, in the stage of Fig. 12(c), the amount of collapse observed in the outer periphery of the wafer also becomes small.

Thereafter, when the polishing proceeds to the stage of FIG. 12(d), the vicinity of the center of the wafer has a concave shape, and the outer periphery of the wafer has a high shape. When grinding is further performed from this stage, when the stage of Fig. 12(e) is reached, the shape from the stage of Fig. 12(d) becomes a more concave shape near the center of the wafer, and the high rise of the wafer periphery becomes larger. . In addition, the thickness of the wafer becomes thinner with respect to the thickness of the carrier sheet.

Based on the above, in order to obtain a wafer having high flatness and less collapse of the periphery of the wafer, the polishing is generally controlled so that the thickness of the wafer and the thickness of the carrier sheet are Almost the same, in the past, this control was done by adjusting the grinding time.

However, in the control performed by adjusting the polishing time, it is difficult to perform the control correctly due to the variation in the time point at which the device is stopped or the influence of the polishing environment. In addition, with the recent miniaturization of the microelectronic device structure or the large diameter of the semiconductor wafer, it is required to have a higher degree of control over the shape of the wafer to be manufactured, particularly for flatness or nanotopography. Therefore, in order to obtain a wafer having a better flatness or a nanotopography, various improvements in the polishing process have been studied.

For example, if the pressure applied from the polishing cloth to the wafer surface during polishing is unevenly distributed in the wafer surface, the polishing rate and the polishing amount in the wafer surface may become uneven, and the wafer may not be polished. flat. As a method for solving such a problem (for example, refer to Patent Document 1), a polishing cloth attached to a fixed plate is used, and a device different from the polishing device is used before attaching it to the fixed plate. A method of compressing the temperature at a temperature higher than that used for grinding and/or a pressure equal to or greater than the pressure at the time of grinding. The polishing cloth as the viscoelastic body immediately undergoes a sharp deformation immediately after the application of the load, and thereafter, a slow deformation occurs. Further, the amount of displacement (thickness reduction) of the polishing cloth when the load is applied is very dependent on the time during which the load is applied, but the existence time of the polishing load may be uneven depending on the position of the polishing cloth. If the existence time of the polishing load is not uniform with the position of the polishing cloth, the amount of displacement of the polishing cloth at each position of the polishing cloth is not uniform, and the flatness of the polished wafer is also impaired. In the method of Patent Document 1, the polishing cloth attached to the fixing plate is compressed under high temperature and high pressure conditions using a device other than the polishing device, and deformation of the polishing cloth that is rapidly performed immediately after the polishing occurs, and the occurrence of the polishing is suppressed. The creeping deformation of the polishing cloth improves the flatness of the wafer and the like.

Advanced technical literature

Patent Document 1: Patent Document 1: JP-A-H11-267978 (Request Item 2, Paragraph [0006] to Paragraph [0008], Paragraph [0022])

However, in the polishing method described in Patent Document 1, although the flatness in the overall shape of the wafer is improved, the effect of suppressing the collapse of the outer periphery of the wafer is not particularly examined. Further, in the general method of adjusting the above-described polishing time and controlling so that the thickness of the wafer and the thickness of the carrier sheet are the same, even in a state where both of them reach the same thickness, the polishing cloth which is an elastic body is pressurized by grinding. The gap between the carrier sheet and the wafer is such that the stress applied to the outer periphery of the wafer cannot be sufficiently dispersed in the carrier sheet, so that the stress cannot be reduced. Therefore, in the usual method of controlling the relationship between the two to perform polishing, even if the polishing time can be accurately adjusted, for example, there is a possibility that the effect of suppressing the collapse of the outer periphery of the wafer cannot be sufficiently obtained. As described above, in the conventional method, since the outer periphery of the wafer cannot be sufficiently suppressed from being collapsed, it is difficult to achieve both the flatness of the outer periphery of the wafer and the flatness in the overall shape of the wafer during polishing, and it is difficult to sufficiently satisfy the requirements in recent years. .

It is an object of the present invention to provide a two-side polishing method for wafers which is capable of achieving good flatness in the overall shape of the wafer and sufficiently suppressing the collapse of the periphery of the wafer.

According to a first aspect of the present invention, there is provided a method for polishing a wafer on both sides, wherein the center plate is provided with a center hole, and the donut-shaped upper plate and the lower plate holder respectively attached to the polishing surface are pressed against the crystal. Round, the slurry is supplied from the slurry supply hole to the wafer, and the upper plate and the lower plate are rotationally driven to The polishing is performed on both sides of the wafer, and the method is characterized in that both the polishing cloth attached to the upper fixed plate and the lower fixed plate are provided with a polishing cloth compression jig to set the outer circumference or the inner circumference of the polishing cloth. One or both of the outer circumferential side compression portion or the inner circumferential side compression portion that is compression-molded in the vertical direction; the width of the outer circumferential side compression portion in the horizontal direction is the compression width A, and the horizontal portion of the inner circumferential side compression portion The width of the direction is the compression width B. When the diameter of the wafer is D, the compression width A satisfies 0.05 × D ≦ A, and the compression width B satisfies 0.30 × D ≧ B.

A second aspect of the invention is the invention according to the first aspect, characterized in that the compressed width A satisfies 0.05 × D ≦ A ≦ 0.30 × D, and the compressed width B satisfies 0.05 × D ≦ B ≦ 0.30 × D.

A third aspect of the invention is the invention according to the first or second aspect, wherein the compressed width A satisfies 0.15 × D ≦ A ≦ 0.25 × D, and the compressed width B satisfies 0.15 × D ≦ B ≦ 0.25 × D.

According to a fourth aspect of the present invention, the compression amount in the vertical direction of the inner circumferential side compression portion and the outer circumferential side compression portion is 0.77% of the thickness of the polishing cloth before compression. the above.

According to a fifth aspect of the invention, in the first aspect of the invention, the outer peripheral side compression unit and the inner circumference side are both provided in the polishing cloth attached to the upper fixed plate and the lower fixed plate. Both.

According to a sixth aspect of the invention, the polishing cloth is a non-woven fabric polishing cloth, a urethane polishing cloth, or a pile surface polishing cloth.

According to a seventh aspect of the invention, the polishing cloth compression jig is a ring shape composed of one part. A jig or a jig composed of two or more parts combined in one ring shape.

According to an eighth aspect of the invention, the polishing cloth compression jig has a thickness of 0.3 mm or more, and is a jig made of an inorganic material or a jig made of a resin.

In the double-side polishing method according to the first aspect of the present invention, the center plate is provided with a center hole, and the donut-shaped upper plate and the lower plate holder, respectively, to which the polishing cloth is attached to the polishing surface, press the wafer, and the slurry is removed from the wafer. a slurry supply hole is supplied to the wafer, and the upper fixed plate and the lower fixed plate are rotationally driven to polish both surfaces of the wafer, and the polishing cloth is attached to the polishing plate and the lower fixed plate respectively In either case, either or both of the outer circumferential side compression portion or the inner circumferential side compression portion that is formed by compressing the outer circumference or the inner circumference of the polishing cloth in the vertical direction by using the polishing cloth compression jig are provided. At this time, the compression width A in the horizontal direction of the outer peripheral side compression portion and the compression width B in the horizontal direction of the inner circumferential side compression portion are controlled so as to satisfy a specific condition with respect to the diameter D of the wafer. In this way, the compressed web in the horizontal direction is appropriately controlled, a part of the polishing cloth is compressed and ground, whereby the stress applied to the outer periphery of the wafer can be suppressed to be larger than even if the polishing cloth sinks by a certain amount during the grinding. Stress applied to the center. Thereby, in the polished wafer, the flatness of the outer periphery of the wafer and the flatness in the overall shape of the wafer can be achieved.

In the double-side polishing method according to the second or third aspect of the present invention, since the compression width A and the compression width B are more appropriately controlled, it is possible to further improve the flatness of the wafer outer circumference and the flatness in the overall shape of the wafer. Degree effect.

In the double-side polishing method according to the fourth aspect of the present invention, the amount of compression in the vertical direction of the inner peripheral side compressed portion and the outer peripheral side compressed portion is controlled so as to be relative to The predetermined ratio of the thickness of the abrasive cloth before compression. Thereby, the stress applied to the outer periphery of the wafer during polishing and the stress applied to the vicinity of the center of the wafer can be made more uniform.

In the double-side polishing method according to the fifth aspect of the present invention, both the outer circumferential side compression portion and the inner circumferential side compression portion are formed in both of the polishing cloths attached to the upper and lower fixed plates, respectively, and the polishing can be further suppressed. There is a strong stress applied to the periphery of the wafer.

In the double-side polishing method according to the sixth aspect of the present invention, a specific polishing cloth such as a non-woven fabric polishing cloth is used as the polishing cloth. Therefore, when the compression web is formed, it is easy to properly adjust and form a horizontal compression belt or a vertical direction. The amount of compression. Further, the compression portion is not easily restored during polishing, and the surface roughness is also good.

In the double-side polishing method according to the seventh aspect of the present invention, a ring-shaped jig composed of one or two or more members is used as the polishing cloth compression jig for forming the inner circumferential side compression portion and the outer circumferential side compression portion. . In this way, by using the ring-shaped jig, the jig can be pinched in a state where the lapping cloth is attached to the upper or lower fixed plate without using other means, and in this simple method, it is possible to accurately A compression portion is formed on the polishing cloth.

In the double-side polishing method according to the eighth aspect of the present invention, the polishing cloth compression jig has a thickness of a specific value or more, and the amount of compression of the polishing cloth in the vertical direction can be easily and accurately controlled to a desired amount. In addition, the jig manufactured using the desired material can be used as a polishing cloth compression jig to prevent contamination of the wafer during polishing by the material used in the manufacture of the polishing cloth compression jig.

11‧‧‧ polishing cloth

11a‧‧‧peripheral compression

11b‧‧‧inner side compression

12‧‧‧Upright

13‧‧‧Offering

14‧‧‧ Carrier

16‧‧‧ Wafer

17‧‧‧Blurry

18‧‧‧Brush supply hole

Fig. 1 is a view showing a polishing apparatus used in the method of the embodiment of the present invention A schematic cross-sectional view of an example.

Fig. 2 is a schematic view showing a state in which wafer polishing is performed by the method of the embodiment of the present invention as seen from above.

Fig. 3 is a cross-sectional view taken along line A-A in Fig. 2.

Fig. 4 is an explanatory view schematically showing the principle that the stress applied to the outer periphery of the wafer is less than that of the past.

Fig. 5 is a schematic view showing an example of a polishing cloth compression jig used in the embodiment of the present invention.

Fig. 6 is a cross-sectional view taken along the line X-Y in Fig. 5.

Fig. 7 is a graph showing the test results in Example 1.

Fig. 8 is a graph showing the results of the test in Example 2.

Fig. 9 is a graph showing the test results in Example 3.

Fig. 10 is a graph showing the evaluation results of the comparison of the outer peripheral shapes in the fourth embodiment.

Fig. 11 is a graph showing the relationship between the amount of compression of the polishing cloth used in the vertical direction and the pressing surface pressure and the standing time after the formation of the compressed portion.

Fig. 12 is a view showing a state in which the shape of the wafer changes in accordance with the elapse of the polishing time in the general double-side polishing process.

Next, the form for carrying out the invention will be described based on the drawings.

The present invention is an improvement of the double-side polishing method, which uses a donut-shaped upper plate and a lower plate holder respectively provided with a center hole at the center portion and a polishing cloth attached to the polishing surface to press the wafer, and the slurry is used. Supplying the slurry from the slurry supply hole to the wafer, and rotationally driving the upper fixed plate and the lower fixed plate to face the wafer Grinding on both sides.

The apparatus used in carrying out the double-side polishing method of the present invention is not particularly limited except for the configuration of the polishing cloth described later, and a general double-side polishing apparatus can be used. For example, the apparatus 10 shown in Fig. 1 is a schematic view showing an example of a double-face polishing apparatus used in the embodiment of the present invention, and the apparatus 10 is a general two-side polishing apparatus in addition to the configuration of the polishing cloth 11. The same structure is formed. In addition, the same symbols in the first to third figures denote the same parts or members.

As shown in Fig. 1, the apparatus 10 has two fixed plates including a donut-shaped upper fixed plate 12 and a lower fixed plate 13 to which the polishing cloth 11 is attached to the polishing surface and the center hole is provided at the center portion. Further, a center gear 21 is provided at a center portion between the upper fixed plate 12 and the lower fixed plate 13, and an internal gear 22 is provided at a peripheral portion. The inner diameter of the inner gear 22 is larger than the outer diameter of the upper fixed plate 12 or the lower fixed plate 13. On the lower fixed plate 13 to which the polishing cloth 11 is attached, a carrier sheet 14 sandwiched by the two fixed plates 12 and 13 is provided, and the wafer 16 is placed as a workpiece to be polished and placed in the holding hole of the carrier sheet 14.

On the other hand, the upper fixing plate 12 is provided with a slurry supply hole 18 for supplying the slurry (polishing liquid) 17, and a supply pipe 19 is provided above the supply hole 18, and the slurry 17 supplied from the supply pipe 19 is provided. It is supplied to the wafer 16 through the supply hole 18. The upper platen 12 is disposed to face the lower fixed plate 13 such that the polishing cloth 11 attached to the upper fixed plate 12 is in contact with the front side surface of the wafer 16, and the crystal in the carrier sheet 14 is pressed by pressurizing the upper fixed plate 12. The circle 16 is pinched by the two fixed plates 12, 13.

On the outer circumference of the carrier piece 14, outer peripheral teeth that mesh with the sun gear 21 and the internal gear 22 are provided. Further, a shaft 20 is provided in the center hole of the two fixed plates 12 and 13, and as the upper fixed plate 12 and the lower fixed plate 13 are rotationally driven by a power source (not shown), the carrier piece 14 is rotated while the center gear 21 is used as the center gear 21 The center conducts a revolution. At this time, the wafer 16 travels in the carrier sheet 14 by the rotation of the carrier sheet 14, as shown in Fig. 1 or Fig. 2.

The present invention is an improvement of the two-side polishing method using the above apparatus, and is characterized in that, on both sides of the polishing cloth 11 attached to the upper fixed plate 12 and the lower fixed plate 13, respectively, the polishing cloth is compressed by a specific compression frame. The jig has either or both of the outer circumferential side compression portion 11a or the inner circumferential side compression portion 11b that is compression-molded in the vertical direction of the outer circumference or the inner circumference of the polishing cloth 11.

In this way, the compressed web in the horizontal direction is appropriately controlled, and a part of the polishing cloth is compressed and polished, and the stress applied to the outer periphery of the wafer can be reduced by the above feature as compared with the case where the compressed portion is not formed. When the wafer is pressed by the upper fixed plate and the lower fixed plate in a state where the compressed portion is not formed, the wafer is pressed against the polishing cloth which is an elastic body, and the polishing cloth is allowed to sink by a certain amount. Therefore, as shown in FIG. 4(a), a large stress is applied to the outer periphery of the wafer 16 by the polishing cloth 11 as compared with the vicinity of the center of the wafer 16. On the other hand, as shown in Fig. 4(b), the outer peripheral side compression portion 11a or the inner peripheral side compression portion 11b is formed by an appropriate compression width, thereby suppressing the outer circumference of the wafer 16 from being near the center of the wafer 16. Big stress. Thereby, during the polishing, the stress applied to the vicinity of the center of the wafer 16 and the outer periphery of the wafer 16 is substantially uniform in the plane. Thereby, overall flatness in the wafer is obtained, and the collapse of the outer periphery of the wafer 16 is suppressed. In general, GBIR to be described later is used as an index indicating the flatness of the overall shape of the wafer 16, and SFQR or ESFQR is used as an index indicating the flatness of the outer periphery of the wafer 16. That is, in the double-side polishing method of the present invention, GBIR and SFQR or ESFQR can be achieved in the wafer 16 after polishing.

Here, the compression width is controlled such that the compression width in the horizontal direction of the outer peripheral side compression portion 11a is A and the compression in the horizontal direction of the inner circumferential side compression portion 11b. When the width is B and the diameter of the wafer 16 is D, the compression width A satisfies 0.05 × D ≦ A, and the compression width B satisfies 0.30 × D ≧ B. During the polishing, the wafer 16 travels to the innermost and outer peripheral portions of the polishing cloth 11 in accordance with the track shown in FIG. By controlling the compression portion as described above, the outer peripheral portion of the wafer 16 is formed on the outer circumferential side compression portion 11a or the inner circumferential side compression portion 11b of the polishing cloth 11 during polishing, thereby reducing the stress applied to the outer periphery of the wafer 16. . The reason why the compression width A and the compression width B are controlled in this way is that, when the compression width A is too small with respect to the diameter D of the wafer 16, in the polishing, the portion passing through the compression portion 11a in the outer periphery of the wafer 16 is changed. Too small, the effect of reducing the stress applied to the periphery of the wafer cannot be sufficiently obtained. On the other hand, with respect to the diameter D of the wafer 16, if the compression web B is too large, the contact surface with the wafer 16 becomes small, so that the stress from the polishing cloth 11 is concentrated on the uncompressed portion of the polishing cloth 11. Strong stress is applied to the wafer 16 from this portion. Therefore, the flatness in the overall shape of the wafer 16 is impaired, and the GBIR is deteriorated. In addition, when the GBIR is deteriorated, the flatness of the outer periphery of the wafer 16 is also impaired, and the evaluation of the ESFQR also has an effect of several nm. Wherein, the control makes the compression amplitude A satisfy 0.05×D≦A≦0.30×D, and satisfies 0.15×D≦A≦0.25×D, so that the compression width B satisfies 0.05×D≦B≦0.30×D, It is better to satisfy 0.15 × D ≦ B ≦ 0.25 × D. Further, as shown in FIG. 3, in the case where the wafer 16 travels to the innermost peripheral portion of the polishing cloth 11 during polishing, the upper compressed portion A or the compressed web B is the outermost peripheral portion of the polishing cloth 11 or The outermost peripheral portion is the width of the outer peripheral side compressed portion 11a or the inner peripheral side compressed portion 11b measured in the horizontal direction. In other words, the compressed width A and the compressed width B in this case are equal to the actual width of the outer circumferential side compression portion 11a or the inner circumferential side compression portion 11b in the horizontal direction. However, as shown in Fig. 1, the wafer 16 does not travel to the outermost peripheral portion or the innermost peripheral portion of the polishing cloth 11 during polishing. The compression width A and the compression width B are respectively compressed by the outer circumferential side compression portion 11a or the inner circumferential side measured as the starting point from the position on the outermost circumference side or the position on the innermost circumference side of the polishing cloth 16 that the wafer 16 is in the middle of polishing. The width of the portion 11b in the horizontal direction. In other words, the compression width A and the compression width B in this case are such that the actual width of the outer circumferential side compression portion 11a or the inner circumferential side compression portion 11b in the horizontal direction is subtracted from the non-walking of the wafer 16 during the polishing. Part of the value after the width in the horizontal direction.

In addition, the amount of compression of the outer peripheral side compression portion 11a and the inner peripheral side compression portion 11b formed in the polishing cloth 11 in the vertical direction is preferably 0.77% or more of the thickness of the polishing cloth 11 before compression. This is because if the amount of compression in the vertical direction is much smaller than this, the effect of reducing the large stress applied to the outer periphery of the wafer when the polishing cloth sinks during polishing may not be obtained. Among them, the amount of compression in the vertical direction is preferably 0.90% or more of the thickness of the polishing cloth before compression. In addition, as shown in FIG. 3, the cross-sectional shape of the outer peripheral side compressed portion 11a and the inner peripheral side compressed portion 11b is formed to be inclined from the center of the polishing cloth 11 toward the compression start position toward the inner circumference or the outer circumference. It may be formed in a shape that is not inclined and whose compression surface is horizontal. In addition, when the outer peripheral side compressed portion 11a and the inner peripheral side compressed portion 11b are formed to be inclined toward the inner circumference or the outer circumference of the polishing cloth 11, the amount of compression in the vertical direction is the position where the compression amount is the largest in the compressed portion. Measured value.

In addition, the one of the outer peripheral side compression part 11a and the inner peripheral side compression part 11b may be formed in one of the polishing cloths, but the outer peripheral side compression part is formed from the viewpoint of sufficiently exhibiting the above effects. Both the 11a and the inner peripheral side compression portion 11b are preferable.

The outer circumferential side compression portion 11a and the inner circumferential side compression portion 11b can be formed using, for example, a ring-shaped polishing cloth compression jig 31 shown in Figs. 5 and 6 . Specifically, after the polishing cloth 11 is attached to, for example, the polishing surface of the upper fixed plate 12 and the lower fixed plate 13, the outer circumference or the inner circumference of the polishing cloth 11 attached to the lower fixed plate 13 is disposed as shown in FIG. The polishing cloth compression jig 31a on the outer peripheral side or the polishing cloth compression jig 31b on the inner peripheral side is pressed by the upper fixed plate 12 and the lower fixed plate 13 under specific conditions. Thereby, the above-described desired compressed portion can be easily formed on the outer circumference or the inner circumference of the polishing cloth 11. In order to prevent, for example, the compression portion from partially recovering during polishing to change the size, the compression conditions at this time are controlled at a compression temperature of 20 to 30 ° C, a compression time of 1 hour or more, and a surface pressure of 500 g/cm ² .

As shown in Fig. 5, the above-mentioned polishing cloth compression jig 31 may be a ring-shaped jig made up of one piece, or may be a jig formed of, for example, two or more parts combined in one ring shape. The cross-sectional shape of the polishing cloth compression jig 31 is not particularly limited, and the cross-sectional shape of the compressed portion to be formed may be, for example, the shape shown in Fig. 6(a) or the shape shown in Fig. 6(b).

Further, the polishing cloth compression jig 31 may be a jig made of stainless steel or titanium, but it is inorganic based on the viewpoint of preventing contamination of the wafer during polishing due to the material used for the manufacture of the jig. A jig formed of a material or a jig made of a resin is preferred. For example, tantalum nitride or zirconium dioxide can be used as the inorganic material. Further, the resin is polyvinyl chloride (PVC) or polytetrafluoroethylene polytetrafluoroethylene. In addition, in order to control the amount of compression in the vertical direction of the outer peripheral side compressed portion 11a or the inner peripheral side compressed portion 11b to the above-described desired amount of compression, the thickness of the polishing cloth compression jig 31 is preferably 0.3 mm or more.

In addition, the polishing cloth 11 attached to the upper fixed plate 12 and the lower fixed plate 13 is not particularly limited, but a non-woven fabric polishing cloth is used because it is easy to form a compressed portion, the compressed portion is not easily restored to the original thickness, and the surface roughness is excellent. Polyurethane A polishing cloth or a suede polishing cloth is preferred.

Further, in the polishing method of the present invention, the specific procedure or other conditions at the time of polishing other than the configuration of the polishing cloth described above are not particularly limited, and can be carried out in accordance with well-known conditions. As described above, with the double-side polishing method of the present invention, it is possible to obtain a good flatness of the overall shape of the wafer in the polished wafer, and it is possible to sufficiently suppress the collapse on the outer periphery of the wafer.

[Examples]

Next, an embodiment of the present invention will be described in detail.

<Example 1>

Using the double-side polishing apparatus 10 shown in Fig. 1, the compression width A and the compression width B of the outer peripheral side compression portion 11a and the inner circumferential side compression portion 11b of the polishing cloth 11 are changed for each test example to perform polishing on both sides of the wafer. Verify that the flatness varies with the variable of the compressed amplitude. The results are shown in Tables 1 and 7 below. Further, in Test Examples 2 to 9 in the first embodiment, as shown in Table 1, the compression width A and the compression width B were changed in accordance with the conditions of the compression width A = compression width B. Further, in Test Example 1, the compression portion was not formed, and the both surfaces of the wafer were polished.

Specifically, first, a non-woven fabric polishing cloth (manufactured by NITTA HASS Co., Ltd.: suba800) having a polishing cloth thickness of 1.3 mm, a hardness (Asker C) of 83, and a compression ratio of 3.3% is prepared as the polishing cloth 11, and the above is written. The polishing cloths 11 are attached to the polishing surfaces of the two fixed plates 12, 13 provided in the apparatus 10, respectively. Thereafter, the two polishing cloth compression jigs 31a and 31b shown in Fig. 5 are disposed on the outer circumference and the inner circumference of the polishing cloth 11 attached to the lower fixed plate 13, respectively, at a compression temperature of 25 ° C and a surface pressure of 500 g/cm ^{2 .} The pressure was clamped under the condition of a compression time of 1 hour. Thereby, the outer peripheral side compression part 11a and the inner peripheral side compression part 11b are formed in both of the polishing cloth 11 attached to the polishing surface of the two fixed plates 12 and 13. Further, in the polishing cloth compression jigs 31a and 31b, a jig of a PVC having a cross-sectional shape as shown in Fig. 6(a) is used.

Then, the carrier sheet 14 having a thickness of 778 μm is placed on the polishing cloth 11 on the lower fixed plate 13 side on which the outer peripheral side compressed portion 11a and the inner peripheral side compressed portion 11b are formed, and the diameter is 300 mm and the thickness is 790 μm. The germanium wafer is placed in the holding hole of the carrier sheet 14 as the object to be polished (wafer 16). Then, the upper wafer 16 provided on the holding hole of the carrier sheet 14 is pinched together with the carrier sheet 14 under the condition of a surface pressure of 300 g/cm ² , and the slurry is supplied from the slurry supply hole 18 (NITTA HASS Co., Ltd. Manufacturing, trade name: nalco 2350) 17, while simultaneously rotating the upper plate 12 and the lower plate 13 to perform double-side grinding of the wafer 16. In addition, the target thickness at this time was 780 μm.

Regarding the flatness of the wafer after the double-side polishing, GBIR and SFQRmax were measured using a measuring device (manufactured by KLA Tencor Co., Ltd., model name: Wafer Sight 2) for evaluation. The measurement conditions at this time were that the measurement range was 296 mm after the outer circumference of the wafer was 2 mm. In addition, the values of GBIR and SFQRmax shown in Tables 1 and 7 are obtained by polishing each of the polishing cloths of each group in which the compression portion is formed under the above-described conditions by using the same conditions and averaging 10 pieces. value. Further, the coefficients α shown in Tables 1 and 7 are such that the compression width A or the compression width B is expressed by the length with respect to the wafer diameter D, that is, A = α × D or B = α × D. The coefficient α . The GBIR (Grobal Backside Ideal focal plane Range) is a value used as an index indicating the flatness of the overall shape of the wafer. The GBIR is obtained by the method described later, and the difference between the maximum thickness and the minimum thickness of the entire wafer is calculated on the basis of the back surface of the wafer in the case where the back surface of the wafer is completely adsorbed.

In addition, SFQR (Site Front least sQuares Randge) is an index indicating the local flatness of the wafer in accordance with the SEMI specification. The SFQR is a full data of the surface positions of the points in the station representing the surface reference, and the reference plane in the station is calculated by the least square method, and the maximum and minimum values of the offset from the plane are taken. And the resulting value, SFQRmax represents the maximum value of the SFQR of the entire station within the wafer.

As is clear from Tables 1 and 7, it is known that when the compression width A and the compression width B are increased such that the coefficient α satisfies a specific condition, the GBIR hardly changes, and the SFQRmax shows a good value (Test Example 2 to Test Example) 7). Further, in particular, the best result was obtained when the coefficient α was 0.20 (Test Example 5). On the other hand, when the coefficient α exceeds 0.30, the flatness is deteriorated, and in Test Example 8 in which the coefficient α is 0.35, the same as Test Example 1 in which the compression width is not formed, SFQRmax shows a bad value, and the coefficient α is 0.40. In Test Example 9, both GBIR and SFQRmax showed values which were much worse than Test Example 1. From this result, it was confirmed that the compression web was controlled such that the coefficient α satisfies a specific condition and is suitable for improving the flatness of the polished surface.

<Example 2>

As shown in Table 2, which will be described later, the compression width A and the compression width B provided on the outer circumferential side compression portion and the inner circumferential side compression portion of the polishing cloth are changed for each test example in accordance with the conditions of the compression width A and the compression width B. The two sides of the wafer are ground to verify that the flatness varies with the variable of the compression web. The results are shown in Tables 2 and 8 below. Further, the conditions and evaluation methods other than the compressed web in each test example of the second embodiment were carried out in the same manner as in the above-described first embodiment.

As is clear from Tables 2 and 8, if the coefficient α is controlled within a specific range, the flatness of the polishing surface can be improved even if the compression width A and the compression width B are not formed into the same compression width.

<Example 3>

The compression portion was formed only on one of the outer circumference and the inner circumference of the polishing cloth, and the compression width was changed within the range shown in Table 3 below to perform both-side polishing of the wafer to verify the change in flatness. The results are shown in Tables 3 and 9 below. Further, the conditions and evaluation methods other than the compressed web in each test example of Example 3 were carried out in the same manner as in the above Example 1.

As can be clearly seen from Tables 3 and 9, it is also possible to see some flatness in the case where the compression portion is formed only in one of the outer circumference or the inner circumference of the polishing cloth, and the compression width is controlled such that the coefficient α satisfies a specific condition. In the case of the reduction, as in Test Example 2 to Test Example 7, etc., the effect of improving the flatness of the polished surface can be sufficiently obtained.

<Example 4>

As a result of the above-described Example 1, the highest evaluation was obtained in Test Example 5 in which the coefficient α was 0.20. Therefore, the two-side polishing of the wafer was performed again under the same conditions as those of Test Example 5, and the evaluation of the peripheral collapse amount was performed. . The results are shown in Tables 4 and 10 below. In addition, the results shown in Tables 4 and 10 are the results obtained by performing the two-surface grinding on the same conditions for each of the test examples and averaging them.

In Table 4, the test example 24 is the same as the test example 1 in the above-described first embodiment, and the polishing cloth is formed by performing the double-side polishing of the wafer without forming the compressed portion, and the test example 25 is the same as in the above-described first embodiment. Test Example 5, the same conditions form compression For example, an example of performing two-side polishing of a wafer. Regarding the conditions at the time of polishing and the evaluation methods of GBIR and SFQRmax, Test Example 24 and Test Example 25 were carried out in the same manner as in each test example in Example 1. The evaluation of the amount of peripheral collapse was also measured by the above-described measuring device (manufactured by KLA Tencor Co., Ltd., model name: Wafer Sight 2).

As is clear from Table 4, almost the same results were obtained in Test Example 24 and Test Example 25 with respect to the value of GBIR. On the other hand, the smaller the value based on SFQRmax, the higher the flatness, and it was found that the test piece 25 in which the desired compression portion was formed in the polishing cloth was improved in flatness as compared with Test Example 24. Fig. 10 shows the shape of the outer peripheral portion of the wafer. It was confirmed that the desired compression portion was formed in the polishing cloth, whereby the amount of collapse in the outer periphery of the wafer was improved.

<Example 5>

Using the same polishing cloth as the polishing cloth used in each of the test examples of Examples 1 to 3, the amount of compression in the vertical direction and the compression surface pressure and the formation of the compression portion when the compression portion was formed in the polishing cloth were started. The relationship between the placement time of the grinding was tested. The result is shown in Fig. 11. Fig. 11 shows the result that the compression surface pressure was 100 to 1000 g/cm ² and the standing time from the formation of the compression portion to the start of the two-side polishing was 10 minutes to 6 hours. Further, even if the standing time exceeded 6 hours, the amount of compression from the time of leaving for 6 hours was not changed (not shown). Further, in the same manner as in each of the test examples of Examples 1 to 3, the compression time at the time of forming the compression portion was 1 hour, and the compression temperature was 25 ° C (room temperature).

In each of the test examples of the above-described Examples 1 to 3, in the test example in which the effect of improving the flatness of the wafer shape was observed, the compression surface pressure was 500 g/cm ² , and the compression portion was formed in the shortest test example. The surface was placed for 10 minutes (compression amount: 17 μm = compression ratio: 1.3%), and double-side polishing was carried out in a state where the longest test example was left for 6 hours (compression amount: 10 μm = compression ratio: 0.77%). According to the results shown in Fig. 11, in these test examples, the amount of compression of the polishing cloth in the vertical direction was 10 μm or more, and from this value, the amount of compression with respect to the thickness (100%) of the polishing cloth before compression was calculated. The amount of compression of the polishing cloth in the vertical direction was 0.77% or more with respect to the thickness of the polishing cloth before compression. From this, it was confirmed that the amount of compression of the compressed portion in the vertical direction is preferably 0.77% or more with respect to the thickness of the polishing cloth before compression.

[Industrial use possibilities]

The present invention can be utilized, for example, in the manufacturing process of a semiconductor wafer typified by a germanium wafer, in order to obtain wafer flatness on both sides of the wafer.

10‧‧‧ device

11‧‧‧ polishing cloth

11a‧‧‧peripheral compression

11b‧‧‧inner side compression

12‧‧‧Upright

13‧‧‧Offering

14‧‧‧ Carrier

16‧‧‧ Wafer

17‧‧‧Blurry

18‧‧‧Brush supply hole

19‧‧‧Supply tube

20‧‧‧Axis

21‧‧‧Center gear

22‧‧‧Internal gear

Claims (8)

A two-side polishing method for a wafer, wherein the wafer is pressed against the wafer by a donut-shaped upper plate and a lower plate holder respectively provided with a center hole in the center portion and a polishing cloth attached to the polishing surface, and the slurry is removed from the wafer a slurry supply hole is supplied to the wafer, and the upper fixed plate and the lower fixed plate are rotationally driven to polish both sides of the wafer, and the method is characterized in that the upper fixed plate and the lower fixed plate are respectively attached One or both of the outer circumferential side compression portion or the inner circumferential side compression portion that is formed by compressing the outer circumference or the inner circumference of the polishing cloth in the vertical direction using the polishing cloth compression jig; The width of the outer peripheral side compressed portion in the horizontal direction is the compressed width A, and the width in the horizontal direction of the inner peripheral side compressed portion is the compressed width B. When the diameter of the wafer is D, the compressed width A satisfies 0.05 × D ≦ A The above compressed amplitude B satisfies 0.30 × D ≧ B. The two-side polishing method for a wafer according to the first aspect of the invention, wherein the compression width A satisfies 0.05 × D ≦ A ≦ 0.30 × D, and the compression width B satisfies 0.05 × D ≦ B ≦ 0.30 × D . The two-side polishing method for a wafer according to the first or second aspect of the invention, wherein the compression width A satisfies 0.15 × D ≦ A ≦ 0.25 × D, and the compression width B satisfies 0.15 × D ≦ B ≦ 0.25 ×D. A two-side polishing method for a wafer according to any one of claims 1 to 3, characterized in that: The amount of compression in the vertical direction of the inner circumferential side compression portion and the outer circumferential side compression portion is 0.77% or more of the thickness of the polishing cloth before compression. The two-side polishing method for a wafer according to any one of claims 1 to 4, wherein the outer peripheral side is provided on both of the polishing cloths attached to the upper and lower fixed plates, respectively. Both the compression unit and the inner circumference side compression unit. The method for polishing a double-sided wafer according to any one of the first to fifth aspects of the invention, wherein the polishing cloth is a non-woven fabric polishing cloth, a urethane polishing cloth or a pile-surface polishing cloth. The two-surface polishing method for a wafer according to any one of the first to sixth aspects of the present invention, wherein the polishing cloth compression jig is a ring-shaped jig composed of one component or a combination A jig made up of two or more ring-shaped parts. The method for polishing a wafer according to any one of claims 1 to 7, wherein the polishing cloth has a thickness of 0.3 mm or more, which is a jig formed of an inorganic material. Or a resin fixture.