WO2002090050A1

WO2002090050A1 - Wafer polishing method and wafer polishing device

Info

Publication number: WO2002090050A1
Application number: PCT/JP2002/004436
Authority: WO
Inventors: Toshihiro Tsuchiya; Hisashi Masumura; Yu Ishii; Norio Kimura
Original assignee: Shin-Etsu Handotai Co., Ltd.; Ebara Corporation
Priority date: 2001-05-08
Filing date: 2002-05-07
Publication date: 2002-11-14
Also published as: TW587969B; JP2002331453A

Abstract

A wafer polishing method comprising the steps of holding a wafer (W) on a holding table (11), and polishing the wafer (W) by pressing it against an abrasive cloth (15) while adding an abrasive (13), wherein the surface to be polished of the wafer (W) is polished by a ring (4) having an inner diameter that is not more than 1.0 mm larger than the diameter of the wafer (W) in such a manner that the portion of the abrasive cloth (15) surrounding the wafer (W) is recessed by an amount of at least 0 mm to not more than 1 mm with respect to the surface to be polished of the wafer (W).

Description

Description: A8 polishing method and A8 polishing apparatus

The present invention relates to a polishing method and a polishing apparatus for polishing a semiconductor wafer, a wafer made of quartz or a ceramic material (hereinafter simply referred to as “A8”): c-8. Background art

研磨 As a polishing device used in the polishing process of A-8, a disk-shaped surface plate with a polishing cloth attached to the surface, and another surface of the polishing cloth holding one surface of the wafer to be polished (A main surface), and a polishing agent supply device for supplying the polishing agent onto the polishing cloth, and the polishing cloth and the polishing cloth are rotated relative to the surface plate.研磨 It is widely known that polishing is performed by supplying an abrasive between the device and A-8. There are various forms of the above-mentioned e-wafer holding plate in order to improve the flatness of the e-hachi. For example, 押圧 a recess having a recess for accommodating the wafer ゥ a vertically movable pressing ring is arranged on the outer periphery of the wafer holding plate, and the pressing force applied to the wafer by the wafer holding plate and the pressing force applied to the polishing cloth by the pressing ring Some of them are independently changed to adjust the polishing amount of the outer peripheral portion of the wafer.

By the way, if the polishing is performed while pressing the wafer against the polishing cloth, the polishing cloth is elastic and bent, so that an excessively polished portion is formed on the outer peripheral portion of the wafer. If this excessively polished portion (hereinafter referred to as “sag”) is located inside the chamfered portion on the outer periphery of the wafer, the flatness of the main surface (polished surface) of the wafer will deteriorate. In particular, in the semiconductor device manufacturing process, the effective area of the wafer as a semiconductor substrate is required to be as large as possible with respect to the entire size of the wafer, but if the above-mentioned sagging is present, the effective area of the wafer is small. Problem arises. In addition, ゥ In the case of polishing in the polishing step, if sag is formed in the polishing step, it is necessary to increase the polishing allowance in order to correct the sag in the subsequent polishing step, and there is also a problem that productivity is reduced. is there.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a polishing method and a polishing apparatus for a wafer, which suppress excessive polishing of an outer peripheral portion of the wafer. Another object of the present invention is to provide a polishing method and a polishing apparatus for flattening a wafer having an outer peripheral portion that is excessively polished. Disclosure of the invention

In order to solve the above-mentioned problems, a polishing method of the present invention is characterized in that a wafer is held on a holding plate, and the wafer is pressed against a polishing cloth and polished while adding an abrasive. In the polishing method, a portion of the polishing cloth surrounding the wafer is at least larger than 0 mm with respect to the surface to be polished of the wafer by a ring having an inner diameter that is not more than 1.0 mm larger than the diameter of the wafer. It is characterized in that the surface to be polished is polished in a recessed state of 1 mm or less.

According to this polishing method, since the polishing cloth is depressed in the above-mentioned range with respect to the surface to be polished of the wafer by the ring, the pressing force on the polishing cloth at the outer peripheral portion of the wafer is weakened. Excessive polishing of the outer peripheral portion is suppressed or suppressed. Therefore, the amount of polishing at the outer peripheral portion can be made substantially uniform with respect to the main surface of the wafer, and sag at the outer peripheral portion of the wafer E can be suppressed. In addition, when sagging is present on the outer peripheral portion of the wafer, polishing of the outer peripheral portion is suppressed, so that sagging can be accurately corrected. Therefore, it is possible to improve the flatness of the device and improve the productivity. The reason why the dent amount of the polishing cloth is set in the above range is that if the polishing cloth is depressed with respect to the surface to be polished of the wafer more than 1 mm, the portion where there is no sag is not polished and the flatness is deteriorated. That's why.

The reason why the inner diameter of the ring was made 1.0 mm or less larger than the diameter of ため This is to leave a gap of 0.5 mm or less between the outer circumference of A-8 and the inside of the ring on average. If it is larger than 1.0 mm, it is necessary to increase the depth of the dent of the polishing cloth in order to weaken the pressing force on the polishing cloth on the outer periphery of the wafer, and the position of the wafer will vary within the ring. This is because the effect of suppressing excessive polishing or suppressing polishing of the outer periphery of the wafer 18 due to the depression of the polishing cloth is not sufficiently obtained, and the effect of preventing or correcting sagging is reduced.

The polishing cloth is a multilayer polishing cloth composed of a nonwoven fabric and an elastic sheet, and it is preferable that the nonwoven fabric is disposed on the side in contact with the sheet. By using this multilayer polishing cloth, the stress at the outer peripheral portion due to the reaction force of the polishing cloth due to the load on the ring can be reduced, and the uniformity at the center can be improved.

Further, it is preferable that the compression rate of the polishing cloth is 2% to 20%, and the compression modulus is 70% to 90%. Since the polishing cloth having such a compressibility and a compressive elasticity has an appropriate hardness, the polishing speed of the abrasive is high, and the control of the amount of dent (deformation) by the ring is easy. If the polishing cloth is too soft, the polishing rate will be slow and precise pressure control to adjust the amount of dents will be required. If the polishing cloth is too hard, it is necessary to increase the pressing force of the ring. It is easy to control the load of the pressing ring with respect to the polishing pressure by making it at least about 2 to 5 times. For a polishing cloth having the above-mentioned compression ratio and compression elastic modulus, the depression amount of the polishing cloth is reduced by such a pressure difference as 0. This is preferable because it can be set larger than 1 mm and within 1 mm.

A polishing apparatus according to the present invention includes: a platen to which a polishing cloth is adhered; a holding plate for holding a wafer; and a polishing agent supply device for supplying a polishing agent, wherein the wafer is pressed against the polishing cloth. A polishing apparatus for polishing while adding an abrasive to the polishing machine, comprising a ring that can move up and down independently of the holding board around the holding board, wherein the ring is 1. It has an inner diameter larger than 0 mm or less, and is configured to protrude from the polishing surface of the wafer to the polishing cloth side by at least more than 0 mm and 1 mm or less. According to this polishing apparatus, the ring has an inner diameter that is larger than the diameter of the A-8 by 1.0 mm or less, and is configured to protrude from the polished surface of the A-8 toward the polishing cloth. The polishing cloth in the portion surrounding is recessed with respect to the surface. That is, the pressing force of the outer peripheral portion of the wafer against the polishing cloth is weakened, and excessive polishing of the outer peripheral portion of the wafer is suppressed or suppressed. Therefore, the amount of polishing at the outer peripheral portion can be made substantially uniform with respect to the principal surface of the outer peripheral portion, so that sagging of the outer peripheral portion of the outer peripheral portion can be suppressed or suppressed. In addition, in the case where droop exists in the outer peripheral portion, polishing can be suppressed in the outer peripheral portion in FIG. 18 so that droop can be corrected. Therefore, the flatness of the wafer can be improved, and the productivity can be improved. If the inner diameter of the ring is greater than 1.0 mm with respect to the diameter of the wafer, the position of the wafer in the ring will vary, and the effect of suppressing excessive polishing or polishing of the outer periphery of the wafer will be reduced. Since the effect of preventing or correcting sagging is reduced due to insufficient yield, the above range was set. The reason why the range of the ring projection is set to the above range is that the sag of the outer peripheral portion inside the chamfered portion can be corrected with high accuracy, particularly by projecting the ring within this range.

The polishing cloth preferably has a compression ratio of 2% to 20% and a compression modulus of 70% to 90%. Since the polishing cloth having such a compressibility and a compressive elasticity has appropriate hardness, the polishing rate is high and the control of the amount of dent (deformation) due to the ring is easy. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic explanatory view of a polishing apparatus of AA8 according to the present invention,

FIG. 2 is a schematic explanatory view of the holding plate of FIG. 1,

FIG. 3 is a diagram showing a relationship between a pressing force and a compression amount with respect to a polishing cloth which is an example of the one used in the present invention.

FIG. 4 is a diagram comparing the outer peripheral shape of the ゥ A before and after polishing when polishing the ゥ wafer with the difference in height between the pressing ring and the polished surface of the ゥ A 8 being about 0.1 mm. FIG. 5 is a diagram comparing the outer peripheral shape of the ゥ A8 before and after polishing when the リング 18 is polished with the difference in height between the pressing ring and the polished surface of the 約 A wafer being about 0 mm. 6 is a diagram comparing the outer peripheral shape of the wafer A before and after polishing when polishing the wafer with the height difference between the pressing ring and the surface to be polished of the wafer being about 1.2 mm, FIG. 7 is a graph comparing the amount of sag improvement with respect to the target polishing allowance while changing the difference between the inner diameter of the pressing ring and the diameter of the ゥ A8. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, with reference to the drawings, a description will be given of a polishing apparatus for AA-8 and a polishing method for AA-8 according to the present invention. However, various modifications are possible without departing from the technical idea of the present invention. Not even.

FIG. 1 is a schematic explanatory view of a polishing apparatus according to the present invention, and FIG. 2 is a schematic explanatory view of a holding plate. The polishing apparatus 10 shown in FIG. 1 includes a holding plate 11 for holding the wafer W, a surface plate 12, and an abrasive supply device 14 for supplying an abrasive 13. A polishing cloth 15 is attached on the surface plate 12. As shown in FIG. 2, the holding plate 11 has a backing pad 1, and the backing pad 1 holds one side (rear surface) of the wafer W with water to hold the wafer W, and a predetermined load is applied. Press the other surface of wafer W (polished surface: main surface) against polishing cloth 15 with. The platen 12 rotates around a rotation axis 16, and the holding plate 11 rotates around a rotation axis 17. The wafer W is polished by rotating the wafer W while supplying the abrasive 13 between the wafer W and the polishing cloth 15 by the abrasive supply device 14.

As shown in FIG. 2, the holding board 11 has a backing pad 1, a ceramic body 2, a pressing block 3, a pressing ring 4, and a ring pressing member 5. The backing pad 1 and the main body 2 are provided with a plurality of through holes 7 penetrating therethrough and connected to the vacuum path 6, and vacuum is generated by a vacuum device (not shown) connected through the vacuum path 6, and Back side of the backing pad 1 by vacuum suction Then, the wafer W can be transported to the loader and unloader.

The pressing ring 4 is formed of ceramics, and has a ring shape surrounding the outer periphery of the wafer W. The vertical section of the pressing ring 4 is substantially square. The inner diameter of the pressing ring 4 is larger than the diameter of the wafer W, but the difference ί (the inner diameter of the pressing ring 4) — (the diameter of the wafer W) is not more than 1.0 mm. A hollow ring pressing member 5 such as an air cylinder or an airbag is arranged on the pressing ring 4 and is connected to an air compressor 8. By sending air from the air compressor 8 into the ring pressing member 5, the pressing ring 4 is pressurized independently of the holding plate 11. For this reason, the pressing ring 4 can move up and down independently of the holding plate 11. The range in which the pressing ring 4 can move up and down is about 2 mm above and below the surface to be polished.

To polish the wafer W with the polishing cloth 15 depressed against the surface to be polished of the wafer W, the entire holding plate 11 is pressed against the polishing cloth 15 and the ring pressing member 5 is pressed. Accordingly, the pressing force of the pressing ring 4 against the polishing cloth 15 is made larger than the pressing force of the wafer W, and the lower end of the pressing ring 4 on the polishing cloth 15 side is more than the polishing cloth 1 at the center of the wafer W. Jump out to the 5 side. Then, as shown in FIG. 2, the polishing pad 15 surrounding the outer periphery of the wafer W sinks down, and becomes concave with respect to the surface to be polished of the wafer W. The amount of depression of the polishing cloth 15, in other words, the difference in height between the lower end of the pressing ring 4 and the surface to be polished at the center of the wafer W during polishing is larger than 0 mm and 1 mm or less. This is because, when the polishing pad 15 is depressed with respect to the surface to be polished of the wafer W by more than 1 mm, the portion where no dripping is present is not polished, and the flatness is deteriorated.

The pressing ring 4 having the above-described inner diameter causes the polishing cloth 15 surrounding the outer periphery of the wafer W to sink below the polishing surface of the wafer W by more than 0 mm and 1 mm or less. The polishing load on the outer peripheral part of ゥ is lower than that of the center part of e-W. In particular, it is important to maintain this condition during polishing. In order to maintain this state stably, it is necessary to make the polishing pad 15 It is advisable to control the pressure ring 4 and the polishing pressure (pressing force of the holding plate 11) independently while grasping the amount of pressure, and to set the pressing force of the pressing ring 4 always higher than the polishing pressure.

By adjusting the amount of depression of the polishing pad 15, that is, by adjusting the protruding height of the pressing ring 4, the pressing force on the portion of the polishing pad 15 corresponding to the outer peripheral portion of the wafer W is weakened. Excessive polishing is suppressed, generation of sag is suppressed, and a wafer W with good flatness can be obtained. In addition, even if sagging occurs in the polishing in the previous step, polishing of the outer peripheral portion of the wafer W is suppressed, so that the sagging can be corrected and a good flatness of 18 W can be obtained. In particular, when the polishing pad 15 is depressed within the above range, the effect of suppressing the occurrence of dripping or correcting the dripping is large.

The reason why the inner diameter of the pressing ring 4 is larger than the diameter of the wafer W by 1.0 mm or less is to provide a gap of about 0.5 mm or less between the pressing ring 4 and the wafer W. is there. This is because, if the gap is large, the movable range of the wafer W in the pressing ring 4 becomes large, the effect that the polishing cloth is depressed does not work effectively, and the effect of suppressing the generation of dripping or the dripping correction is sufficient. Because it cannot be used in Further, if the polishing is performed in a state where the deviation is large, a thickness distribution is generated in the eight surfaces of the layer A, and the flatness may be deteriorated.

The polishing cloth 15 is not particularly limited, but it is preferable to use a multi-layer polishing cloth using a polishing cloth 15a made of a nonwoven fabric for the surface layer and an elastic sheet 15b for the lower layer. The compression ratio of the polishing pad 15 is preferably 2% to 20%, and the compression modulus is preferably 70% to 90%.

Here, the compression ratio and the compression elastic modulus of the polishing pad are obtained as follows. First, a thickness T1 one minute after the initial load W0 is applied is measured. At the same time, increase the load to W1 and measure the thickness T2 one minute later. At the same time, set the load to zero, leave it for 1 minute, and apply W 0 again. Measure the thickness T3 1 minute after loading. Then, each value is obtained by the following equation. In the present invention, W0 was evaluated at 30 kPa and W1 was evaluated at 180 kPa. Compression ratio (%) = {(T 1 -Τ 2) / Τ 1} X 100

Compression modulus (%) = {(Τ 3 -Τ2) / (Τ1 -Τ2)} X 100

For the effect of the depression of the polishing pad 15 and the mirror polishing of the wafer W, a polishing pad having the above values is preferable. FIG. 3 shows the relationship between the pressing force (kPa) and the amount of compression (m) against a polishing cloth having a compression rate of 8% and a compression elasticity of 88%, which is an example of the above polishing cloth. For example, when the polishing pressure of wafer W is 30 kPa, this polishing cloth is compressed by about 110 m. When the pressing ring 4 is pressed against the polishing cloth at 120 kPa, which is four times the polishing pressure of the wafer W, the polishing cloth corresponding to the pressing ring 4 is compressed by about 190. In other words, the portion of the polishing pad surrounding the periphery of wafer W is recessed by about 80 m with respect to the surface to be polished of wafer W. In the case of using the pressing ring 4 having the inner diameter in the above range, the sagging can be suppressed or the sagging correction effect can be sufficiently obtained by maintaining the concave amount of the polishing pad 15 at about 80 m.

Regardless of the polishing cloth, the pressure applied to the polishing cloth 15 and the amount of depression (compression) of the polishing cloth 15 at that time as shown in Fig. 3 are checked in advance. By adjusting the difference and setting the amount of deformation of the polishing pad 15 to be larger than 0 mm and within 1 mm, a wafer W having high flatness to the outer periphery can be manufactured. In other words, the amount of dents can be adjusted with any kind of polishing cloth, and there is no particular limitation.However, if the softness is too soft, the polishing capacity will decrease, mainly the polishing rate will decrease. The compression modulus is preferably 20% to 70% to 90%.

The pressing force of the pressing ring 4 is determined according to the amount of compression of the polishing cloth 15, but in the case of the above-described polishing cloth with a compression ratio of 8%, the pressing amount is sufficient if the recess amount of the polishing cloth 15 is 1 mm or less. The higher the value is, the greater the effect of suppressing the sag or correcting the sag. However, in consideration of the pressing ability of the polishing apparatus 10, it is preferable that the pressing force against the wafer W be larger than about 10 times. More preferably, it is about 2 to 5 times. When the difference between the polishing pressure and the pressing force of the pressing ring 4 is kept constant in consideration of the compression amount of the polishing pad 15, the polishing pad 15 can always be maintained in a constant concave shape. A method for polishing a wafer w using the polishing apparatus 10 will be described. First, the back surface of the wafer W is held on the holding plate 11 by the backing pad 1 and the entire holding plate 11 is pressed against the polishing pad 15 with a predetermined load. At this time, air is sent into the ring pressing member 5 by the air compressor 8, and the pressing force of the pressing ring 4 against the polishing cloth 15 is made larger than the pressing force of the wafer W against the polishing cloth 15. As a result, the polishing pad 15 surrounding the outer periphery of the wafer W is sunk by the pressing ring 4 so as to be recessed with respect to the surface to be polished of the wafer W. Then, the platen 12 is rotated about the rotation axis 16, and the holding plate 11 is rotated about the rotation axis 17. By rotating the wafer W while supplying the abrasive 13 between the wafer W and the polishing pad 15 from the abrasive supply device 14, the wafer W can be ground while suppressing the polishing of the outer peripheral portion of the wafer W. Polish.

(Example 1)

A silicon wafer having a diameter of 200 mm was used as the wafer to be polished. This wafer is a wafer in which a chamfered portion is formed with a width of 0.5 mm from the outermost periphery and a sag exists within a range of about 7 mm inward from the chamfered portion. There use a polishing apparatus 1 0 of the present invention, while adding an abrasive containing colloidal silica power, compression ratio 8.0 ⁰ I compressive modulus using 8 8% polishing cloth as a polishing The main surface of the workpiece to be polished was polished at a pressure of 30 kPa. More specifically, a multilayer obtained by laminating a non-woven fabric of Suba 400 commercially available from Rodell Niyusha Co., Ltd. and a polymer sheet of SE-400 commercially available from Sun Polymer Co., Ltd. A polishing cloth was used.

The press ring used had an inner diameter that was 1.0 mm larger than the diameter of the diameter (press ring inner diameter 20 lmm). As a result, a gap of about 0.5 mm is formed on the average between the inner side of the pressing ring and the outer periphery of the PA8. The pressing ring was pressed against the polishing cloth with a pressure of 150 kPa, and the portion of the polishing cloth that was in contact with the pressing ring was forcibly depressed and polished. At this time, the difference in height between the pressing ring and the surface to be polished is approximately 0.1 mm. Under these conditions, the target polishing allowance of the wafer to be polished was 1.5 m, and the outer peripheral shape of the wafer was compared before and after polishing.

(Comparative Example 1)

Polishing was performed under the same conditions as in Example 1 except that the pressure of the pressing ring was set to the same pressure (30 kPa) as the pressing force of the polishing target. Compared. At this time, the difference in height between the pressing ring and the surface to be polished is about O mm.

FIG. 4 is a comparison of the outer peripheral shape of the PA8 before and after polishing in Example 1. The vertical axis is based on the shape of the ゥ A8, specifically, the thickness at the center of the ハ Eh (about 7 mm from the outer circumference to the center of the ハ Ah, the thickness at the position of 7 mm from the outer circumference was almost flat). It is the value (m) obtained by calculating the thickness at each position within a range of 7 mm from the outer circumference, and calculating the difference {(thickness at each position) 1 (thickness at the center of the wafer)}. The horizontal axis indicates the distance (mm) from the outer periphery of the wafer. FIG. 5 shows the outer peripheral shape of the wafer when polished in Comparative Example 1, as in FIG. As a result, it can be seen that in Example 1, the difference in thickness was reduced at about 1.5 to 6 mm from the outer periphery as compared to before polishing, and the sag was improved. On the other hand, in Comparative Example 1, the shape itself did not change so much, and the sag was not corrected. In other words, it can be understood that deforming the polishing cloth in a concave shape is effective for reducing sagging.

In the polishing cloths used in Example 1 and Comparative Example 1, as the pressure of the pressing ring was increased, the sag at the outer periphery of the wafer was more improved. Due to the strength of the pressing ring itself in Example 1, pressing could only be performed up to about 200 kPa, but the difference in height between the pressing ring and the surface to be polished at this time was 0 to 0. It could be adjusted at 2 mm.

(Comparative Example 2)

Other polishing cloths were used to further confirm the relationship between the pressure ring and the surface to be polished. In Comparative Example 2, using the polishing apparatus 10 of the present invention, a polishing cloth having a compressibility of 20% and a compression elastic modulus of 70% was used as a polishing cloth while adding an abrasive containing colloidal silica. The main surface of the wafer to be polished was polished at a polishing pressure of 30 kPa. In particular, A multilayer polishing cloth was used in which a suede-type polishing cloth was used as a surface layer and a biological sheet using sponge-like silicone was laminated. Also, except that the pressure of the pressing ring was set to the maximum value of 200 kPa of the apparatus used this time, the same wafer as in Example 1 was polished under the same conditions, and the outer peripheral shape of the wafer was adjusted. Was compared before and after polishing. At this time, the difference in height between the pressing ring and the surface to be polished is about 1.2 mm.

Figure 6 shows the results. FIG. 6 is similar to FIG. From FIG. 6, it can be seen that, although the sagging was improved, the outer peripheral portion was thicker than the center and was warped, which was not preferable.

The polishing cloth used in Comparative Example 2 was a softer polishing cloth than that used in Example 1. With the polishing cloth used in Comparative Example 2, the pressure of the pressing ring was adjusted, and the relationship between the height difference between the pressing ring and the surface to be polished and the sag was confirmed. If the difference was larger than 0 mm and kept within 1.0 mm, dripping could be effectively improved. In particular, with this polishing cloth, polishing was performed with a very small sag at the outer peripheral portion of the wafer by adjusting the polishing cloth in the range of 0.05 mm to 0.5 mm.

That is, when the difference in height between the pressing ring and the surface to be polished becomes larger than 0 mm, the sag is gradually improved. On the other hand, if it exceeds 1.0 mm, if the polishing allowance is small, the outer peripheral portion is not polished, and even if the polishing allowance is large, a large warp as in Comparative Example 2 may be seen, which is not preferable. .

(Example 2)

Pressing rings whose inner diameter was 0.4 mm larger than the diameter of the wafer were used, and the targets for the polishing allowance were 0.5 m, 1.0 xm, 1.5 m, and 2.0 m.

(Example 3)

A pressing ring whose inner diameter was larger than the diameter of the wafer by 1.0 mm was used, and the target of the polishing allowance was 0.5 m, 1.0 τη, 1.5 m, and 2.0 m.

(Comparative Example 3)

Use a pressure ring whose inner diameter is 4.0mm larger than the diameter of the wafer. The target of the polishing allowance was set to 0.5 m, 1.0 m, 1.5 m, and 2.0 m. In Example 2, Example 3, and Comparative Example 3, the same type of polishing cloth and polishing cloth as those in Example 1 were used. Then, using the polishing apparatus 10 of the present invention, while adding an abrasive containing colloidal silica, the main surface of the wafer was polished at a polishing pressure of 30 kPa and a pressing pressure of a pressing ring of 120 kPa. did. At this time, the difference in height between the pressing ring and the surface to be polished is about 80 m.

FIG. 7 is a graph showing the sag improvement amount (m) in a region 7 mm from the outer periphery of the wafer with respect to each target polishing allowance m) of Example 2, Example 3, and Comparative Example 3.ダ The amount of sag improvement in the area 7 mm from the periphery of the wafer is defined as the difference from the thickness at 2.0 mm from the periphery of the wafer, based on the thickness of the wafer at a position 7 mm from the periphery of the wafer. ) M) was determined, and this difference was compared before and after polishing to determine the sag difference (amount of improvement).

From FIG. 7, it can be seen that in the case of Example 3, the amount of improvement in sag is greatest. For example, in the region of 7 mm from the outer circumference, to reduce the sag by 0.1 0 ^ πι, the polishing allowance should be about 1.1 in the case of the third embodiment, but the polishing allowance should be approximately 1.1 in the case of the second embodiment. In the case of Comparative Example 3, a polishing allowance of about 2.8 zm is required. Therefore, if the polishing is performed under the conditions of the third embodiment, the effect of improving the sag is high even with a small polishing allowance. In other words, it was found that it is best to keep the gap so that there is a gap of about 0.5 mm around the periphery of the wafer (the inner diameter of the pressing ring is 1 mm larger than the diameter of the wafer). From this result, it can be seen that the effect of suppressing or improving sagging is small by simply pressing the polishing cloth with the pressing ring, and that the effect is small if there is a gap at a certain interval around the periphery of the wafer.

In the above embodiment, the vertical section of the pressing ring is substantially square, but is not limited to this, and may be rectangular, circular, elliptical or the like. Industrial applicability The effect of the representative embodiment of the present invention is as follows. A ring having an inner diameter of not more than 1.0 mm larger than the diameter of the wafer is used to reduce the polishing cloth surrounding the wafer to the wafer. As a result, the pressing force against the polishing cloth on the outer periphery of the sheet 18 is weakened, and excessive polishing of the outer periphery of the sheet A 8 is suppressed. Therefore, the amount of polishing on the outer peripheral portion can be made substantially uniform with respect to the main surface of the layer 18, so that dripping of the outer peripheral portion of the layer 18 can be suppressed. Further, in the case where sagging is present on the outer peripheral portion, polishing of the outer peripheral portion of the wafer can be suppressed, so that sagging can be corrected. Therefore, the flatness of wafers can be improved, and productivity can be improved. Accordingly, the polishing method and wafer polishing apparatus of the present invention are particularly suitable for polishing semiconductor wafers, wafers of quartz and ceramic materials, and the like.

Claims

The scope of the claims

1. A wafer polishing method in which the wafer is held on a holding plate, and the wafer is pressed against a polishing cloth and polished while adding an abrasive, the inner diameter of the wafer being 1.0 mm or less larger than the diameter of the wafer. A surface to be polished is polished while a portion of the polishing cloth surrounding the wafer is recessed by at least more than 0 mm and not more than 1 mm with respect to the surface to be polished by the ring. A8 polishing method.

2. The polishing cloth according to claim 1, wherein the polishing cloth is a multi-layer polishing cloth composed of a nonwoven fabric and an elastic sheet, wherein the nonwoven fabric is arranged on a side in contact with the nonwoven fabric.ゥ A8 polishing method.

3. The polishing method according to claim 1, wherein a compression ratio of the polishing cloth is 2% to 20%, and a compression elastic modulus is 70% to 90%. Method.

4. A surface plate on which a polishing cloth is stuck, a holding plate for holding the wafer, and a polishing agent supply device for supplying the polishing agent, wherein the polishing agent is pressed against the polishing cloth to add the polishing agent. In a wafer polishing machine that grinds while polishing,

A ring that is movable up and down independently of the holding plate around the holding plate, the ring has an inner diameter that is 1.0 mm or less larger than the diameter of the wafer, and the polished surface of the wafer. 18. The polishing apparatus according to item 18, wherein the polishing apparatus is configured to be able to protrude more than 0 mm and 1 mm or less toward the polishing cloth side.

5. The polishing of the wafer according to claim 4, wherein a compression ratio of the polishing cloth is 2% to 20%, and a compression modulus is 70% to 90%. apparatus.