JPH11239964A - Back pad, its manufacture and waxless mounting type polishing device using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of an uneven thickness of a semiconductor wafer caused by a smashed peripheral part of a back pad when polishing its surface and to reduce a damage when polishing the semiconductor wafer. SOLUTION: In a back pad 31 to serve as a backing material of a silicon wafer 19, the hardness of its peripheral part is made to be higher than that of a center part 32. Therefore, an uneven thickness of a silicon wafer 19 caused by a smashed peripheral part of the back pad 31 when polishing its surface can be prevented. The center part 32 of the back pad 31 absorbs an impact force during surface polishing, and thus, when polishing the silicon wafer, a damage can be comparatively reduced. In addition, a damage in a circumferential shape is never produced on a back face of the wafer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a back pad, a method for manufacturing the same, and a waxless mount type polishing apparatus using the back pad. The present invention relates to an improvement of a back pad in a waxless mount type polishing apparatus capable of performing mechanical chemical polishing on a back pad.

[0002]

2. Description of the Related Art A waxless mount type polishing apparatus has been known as a kind of polishing apparatus for a silicon wafer. As shown in FIG. 5, the apparatus comprises a lower surface plate (polishing side surface plate) 104 having an upper surface on which a polishing cloth 105 is stretched;
An upper surface plate (fixed side surface plate) 101 provided with a guide ring 102 for fixing a wafer on the lower surface is provided. A back pad 103 made of a relatively soft nonwoven fabric having water retention property is accommodated inside the guide ring 102. Things. When polishing the surface of the silicon wafer 100, the back pad 10
3 is supplied with pure water or the like, and the silicon wafer 100 is held from the back side by the surface tension. At this time, the silicon wafer 100 is held by the guide ring 102 such that the polishing surface protrudes from the lower edge of the back pad 103. Then, the polishing surface of the silicon wafer 100 is mirror-polished by the polishing cloth 105 by rotating and revolving the upper platen 101 on the lower platen 104 while supplying an abrasive containing abrasive grains to the polishing surface. . The silicon wafer 100 is driven and rotated by an upper surface plate (polishing head) while being fixed to the back pad 103.

[0003]

However, such a conventional waxless mount type polishing apparatus has the following inconveniences. That is, since the back pad was made of a relatively soft nonwoven fabric, the shape retention at the outer periphery of the back pad was poor. Specifically, surface pressure is applied to the silicon wafer during surface polishing from the upper surface plate side. In addition, a revolving force accompanying rotation such as the movement of a planetary gear is also applied. The surface pressure of the upper stool is not uniform microscopically over the entire surface.

Therefore, as shown in FIG. 5, during polishing of the surface of the silicon wafer 100, these combined forces are
The silicon wafer 100 whose horizontal movement is restricted by the guide ring 102 is unevenly distributed on the outer peripheral portion of the back pad 103. As a result, a phenomenon has occurred in which the outer peripheral portion of the back pad 103 is crushed. Therefore, the outer periphery of the silicon wafer 100 is finished in a warped state (a state in which the outer periphery stands) as shown in FIG. That is, there is a problem in that the silicon wafer 100 having a larger outer peripheral portion than the central portion of the wafer is completed, and the thickness of the silicon wafer 100 becomes uneven.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a waxless mount type polishing apparatus capable of preventing the occurrence of thickness unevenness of a semiconductor wafer due to the collapse of the outer periphery of a back pad during surface polishing. For that purpose. It is another object of the present invention to provide a waxless mount type polishing apparatus capable of reducing damage during polishing of a semiconductor wafer. Another object of the present invention is to provide a waxless mount type polishing apparatus that does not cause scratches on the back surface of a semiconductor wafer.

[0006]

According to a first aspect of the present invention, there is provided a waxless mount type polishing apparatus, which is used for holding a semiconductor wafer and has a substantially circular outer shape. The outer peripheral portion is a back pad whose hardness is higher than that of the central portion. The hardness of the outer peripheral portion is, for example, 35 to 55, preferably 40 to 50 by a Shore A hardness meter.

According to a second aspect of the present invention, there is provided the back pad manufacturing method according to the first aspect, wherein the outer periphery of the back pad having a substantially circular appearance is formed to have a higher hardness than the center thereof. It is a manufacturing method.

[0008] The invention according to claim 3 is a step of preparing a substantially circular sheet-like nonwoven fabric, a step of hot-pressing only the outer peripheral portion of the nonwoven fabric to increase the hardness, and thereafter, a step of reducing the thickness of the nonwoven fabric by its thickness 3. The method of manufacturing a back pad according to claim 2, further comprising the step of: forming a back pad having an outer peripheral portion having a higher hardness than a central portion by forming the back pad to be uniform.

According to a fourth aspect of the present invention, there is provided a polishing-side platen on which a polishing cloth is spread on the surface, and a guide ring for fixing the wafer is provided on the surface, which is disposed to face the polishing-side platen. With a fixed side surface plate, and inside this guide ring,
In a waxless mount type polishing apparatus in which a back pad holding a semiconductor wafer with water retention is stored, the back pad has a substantially circular outer shape and a peripheral portion having a higher hardness than a central portion thereof. It is a less mount type polishing machine.

As a material of the back pad, for example, a non-woven fabric such as a suede cloth can be used. The thickness of the back pad is preferably 2 mm or less, and if it exceeds 2 mm, the hardness of the back pad is likely to be uneven. The ratio of the surface area of the high hardness outer peripheral portion to the surface area of the back pad is 10 to
30%, especially 15-20% is preferred. If it is less than 10%, sagging of the outer peripheral portion of the wafer is likely to occur, and if it exceeds 30%, a step is easily formed in the wafer surface.

As described above, a back pad having an outer peripheral portion having a higher hardness than a central portion has, for example, a relatively low-hardness pad disposed at the central portion and a relatively high-hardness pad disposed at the outer peripheral portion. You may arrange | position and adhere | attach both. In this case, the material at the center of the pad may be different from the material at the outer periphery of the pad. In addition, for example, the outer peripheral portion is made higher in hardness from the central portion of the back pad in multiple stages, and further,
The outer peripheral portion of the back pad can be continuously hardened as compared with the central portion. In this polishing apparatus, the polishing-side platen may be a lower platen, and the fixed-side platen may be an upper platen, or may be arranged upside down.

[0012]

According to the present invention, when polishing the surface of the semiconductor wafer, after supplying pure water or the like to the back pad in advance, the semiconductor wafer is housed in the guide ring so that the polished surface of the semiconductor wafer is higher than the guide ring. . As a result, the semiconductor wafer is sucked and held on the back pad. Then, the fixed-side platen is rotated and revolved on the polishing-side platen while supplying an abrasive containing abrasive grains, and the polished surface of the semiconductor wafer is polished with a polishing cloth.

At this time, since the outer peripheral portion of the back pad has higher hardness than the central portion, the shape retention of the back pad from the back side of the wafer, particularly the shape retention of the outer peripheral portion of the back pad is good. Becomes The hardness of the outer peripheral portion is, for example, 35 to 55, preferably 40 to 50 by a Shore A hardness meter. That is, during the surface polishing, even if the combined force of the pressing force, the rotation force, and the revolving force of the fixed surface plate concentrates on the outer peripheral portion of the back pad whose movement is restricted by the guide ring, The part is not easily crushed. As described above, since the outer peripheral portion of the semiconductor wafer during surface polishing is maintained in shape from the back side by the back pad, the thickness of the central portion and the outer peripheral portion of the polished semiconductor wafer are substantially equal. A semiconductor wafer with small unevenness can be obtained. Also, even if a relatively large polishing impact acts on the semiconductor wafer during polishing of the semiconductor wafer surface, the force is absorbed by the relatively soft central portion of the back pad. Therefore, damage during polishing of the semiconductor wafer can be reduced.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. First, a waxless mount type polishing apparatus using a back pad according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a front view of a waxless mount type polishing apparatus according to one embodiment of the present invention. FIG. 2 is a perspective view of a back pad according to one embodiment. FIG. 3 is a front view showing a state during polishing of the surface of the silicon wafer of one embodiment. FIG. 4 is a schematic view showing a manufacturing process of the back pad.

In FIG. 1, reference numeral 30 denotes a waxless mount type polishing apparatus according to an embodiment. The waxless mount type polishing apparatus 30 includes a lower platen 13 and an upper A platen 15 is provided. The lower surface plate 13 which is an example of the polishing-side surface plate has a polishing cloth 12 spread on the upper surface thereof via a thick sponge rubber 11.
An upper surface plate (polishing head) 15 which is an example of the fixed side surface plate,
A guide ring 14 for fixing the wafer is provided on the lower surface. The lower surface plate 13 and the upper surface plate 15 are both disk-shaped, and their opposing surfaces are flat. These lower platen 13 and upper platen 15
It is configured to be rotatable about an axis by rotating means (not shown) via the ports 6 and 17. The upper surface plate 15 is configured to be able to move up and down by moving the rotating shaft 17 up and down.

Inside the guide ring 14 which is a circular ring, a back pad 31 is housed and held with its upper surface in contact with the lower surface of the upper platen 15. As shown in FIGS. 2 and 3, the back pad 31 is made of suede as an example of a nonwoven fabric, and has a thickness of 15
The thickness is slightly larger than that of a silicon wafer 19 which is an example of a 6-inch semiconductor wafer. The back pad 31 has two portions, a central portion 32 having a predetermined hardness and an outer peripheral portion 33 having a higher hardness. The surface area of the back pad 31 is such that the outer peripheral portion 33 has a predetermined elastic force (flexibility) in the thickness direction while the outer peripheral portion 33 has a higher hardness than the central portion 32. About 15%.
The hardness of the outer peripheral portion 33 is, for example, 35 by a Shore A hardness tester.
~ 55, preferably 40 ~ 50. The silicon wafer 19 to be polished is a CZ wafer and has a thickness of 625 μm.

Next, a description will be given of a waxless polishing method for the silicon wafer 19 using the waxless mount type polishing apparatus 30 according to this embodiment. As shown in FIG.
At the time of polishing the surface of the silicon wafer 19, the guide ring 14 is mounted, and pure water or the like is supplied to the back pad 31 held by the guide ring 14. The pure water is held by the back pad 31. After that, the silicon wafer 19 is accommodated in the guide ring 14. At this time,
It is set so that the wafer polishing surface is located below the lower end surface of the guide ring 14. Thereby, the silicon wafer 19 is adsorbed and held on the back pad 31 by the surface tension of the retained water. Thereafter, the upper platen 15 is rotated and revolved on the lower platen 13 while supplying an abrasive containing abrasive grains, and the polishing surface of the silicon wafer 19 is polished by the polishing cloth 12.

At this time, since the back pad 31 has a predetermined flexibility in the thickness direction as a whole pad, a suitable cushioning property of the silicon wafer 19 at the time of surface polishing can be sufficiently ensured. With back pad 3
1 is that the outer peripheral portion 33 is higher in hardness than the central portion 32,
The shape retention of the back pad 31, especially the shape retention of the outer peripheral portion of the pad, is good. Therefore, even if the combined force of the pressing force, the rotation force, and the revolving force of the upper platen 15 concentrates on the outer peripheral portion of the back pad 31 whose movement is restricted by the guide ring 14 during the surface polishing, Is hard to be crushed.

As described above, the outer peripheral portion of the silicon wafer 19 at the time of surface polishing is backed by the back pad 31 having a small amount of deformation.
Is that the thickness of the central portion 32 and the outer peripheral portion 33 are substantially equal,
A silicon wafer with small thickness unevenness is obtained. Since the back pad 31 is divided into the relatively soft central portion 32 and the relatively hard outer peripheral portion 33, a relatively large polishing impact acts on the silicon wafer 19 during polishing of the wafer surface. However, since the impact force is absorbed by the relatively soft central portion 32 of the back pad 31, damage to the silicon wafer 31 during the surface polishing can be suppressed as compared with the case of the embodiment. Also,
Since the silicon wafer 19 is held and polished by the back pad 31, it is possible to prevent the back surface scratch from being caused by the relative movement of the silicon wafer 19 with the back pad 31. If the silicon wafer held by the guide ring 14 rotates freely on the back pad 31 during polishing, groove-like scratches may be generated in the circumferential direction due to the relative rotation.

FIG. 4 shows a method of manufacturing a back pad having different hardnesses in the radial direction. In this manufacturing method, first, a circular nonwoven fabric 4 having a predetermined thickness and a predetermined size is used.
Prepare 8 The nonwoven fabric is a thermosetting material. Therefore, the nonwoven fabric 48 in this state has a predetermined hardness uniformly over the entire surface. And hot press 4
9, only the outer peripheral portion 50 of the circular nonwoven fabric 48 is pressed. As a result, a processed nonwoven fabric having a cross-sectional shape that is convex and thick at the center and thin at the outer periphery thereof is produced. Then, this convex part is cut. As a result, a back pad 51 having a uniform thickness and a different hardness in the radial direction can be obtained.

It is to be noted that the lower end surface of the hot press mold may be tapered. The press die lower surface is formed with an inclined surface such that the inner side of the back pad is located on the upper side and the outer side of the back pad is located on the lower side. As a result, a back pad whose hardness continuously changes in the radial direction can be easily formed. In addition, two back pads of different hardness
A desired back pad can also be formed by preparing these and combining them. In this case, the hard back pad cloth is formed in a donut shape, and the soft back pad cloth is formed in a circular shape so as to enter the hole.
Further, in manufacturing this back pad, a back pad having a different thickness in the radial direction can be formed instead of the back pad having a uniform thickness. This is used directly after hot pressing by the manufacturing method shown in FIG. This is to remove surface cutting from the process.
If such a back pad is used, mirror polishing of an extremely thin silicon wafer or the like can be easily performed.

[0022]

According to the back pad and the waxless mount type polishing apparatus using the same according to the present invention,
By forming the outer periphery of the back pad, which is the backing material of the semiconductor wafer, harder than the center, it is possible to prevent uneven thickness of the semiconductor wafer due to the collapse of the outer periphery of the back pad during surface polishing can do. Further, the impact force during the surface polishing is absorbed by the central portion of the back pad, thereby making it possible to relatively reduce damage during polishing of the semiconductor wafer. Further, according to the polishing apparatus of the present invention, no scratch is formed on the back surface of the semiconductor wafer. This is because the semiconductor wafer is fixedly supported by the back pad during polishing. ADVANTAGE OF THE INVENTION According to the manufacturing method of the back pad which concerns on this invention, the back pad from which hardness differs in a radial direction can be manufactured easily.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a waxless mount type polishing apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view of a back pad according to one embodiment of the present invention.

FIG. 3 is a longitudinal sectional view showing a surface polishing state of a silicon wafer according to one embodiment of the present invention.

FIG. 4 is a schematic view showing a manufacturing process of a back pad according to one embodiment of the present invention.

FIG. 5 is a vertical sectional view showing a state in which a conventional waxless mount type polishing apparatus is polishing a wafer surface.

[Explanation of symbols]

 Reference Signs List 30 waxless mount type polishing machine, 12 polishing cloth, 13 lower surface plate (polishing side surface plate), 14 guide ring, 15 upper surface plate (fixed side surface plate), 19 silicon wafer (semiconductor wafer), 31 back pad, 32 Center part (low hardness part) 33 Outer part (high hardness part) 49 Hot press.

Claims (4)

[Claims] 1. A back pad which is used for holding a semiconductor wafer in a waxless mount type polishing apparatus and has a substantially circular outer shape, wherein an outer peripheral portion has a higher hardness than a central portion thereof. pad. 2. The method for manufacturing a back pad according to claim 1, wherein an outer peripheral portion of the substantially circular back pad is formed to have a higher hardness than a central portion thereof. 3. A step of preparing a substantially circular sheet-like non-woven fabric, a step of hot-pressing only the outer peripheral portion of the non-woven fabric to increase hardness, and thereafter, the non-woven fabric is made to have a uniform thickness. 3. The method of manufacturing a back pad according to claim 2, further comprising: forming a back pad having an outer peripheral portion having a higher hardness than a central portion by forming the back pad. 4. A polishing-side platen on which a polishing cloth is spread on a surface, and a fixed-side platen disposed opposite to the polishing-side platen and provided with a guide ring for fixing a wafer on the surface. In a waxless mount type polishing apparatus in which a back pad having a water retention property and holding a semiconductor wafer is stored inside the guide ring, the back pad has a substantially circular outer shape and an outer peripheral portion thereof. Waxless mount type polishing machine with higher hardness than its central part.