JPH11239963A - Waxless mounting type polishing device - 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. SOLUTION: After storing a back pad 18 containing water in a water holding hole 18a in a guide ring 14 of a silicon wafer 19, a surface of the wafer 19 is polished by rotating an upper surface plate 15 on its axis and revolving it around on an lower surface plate 13 while supplying a polishing liquid. Since the pad 18 is made of a synthetic resin sheet with moderate hardness in comparison with conventional non woven fabric and ice frozen on the surface of the pad 18 becomes a cushion, the wafer 19 is by a moderate elastic holding force and a peripheral part of the pad 18 is kept in a good shape. Since the wafer 19 is held by the pad 18 so as to freely rotate, even if a composite force is concentrated on the peripheral part of the pad from the side of the upper surface plate 15, it is not easily smashed. As a result, the wafer 19 with a small uneven thickness can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wax-less mount type polishing apparatus, and more particularly to a wax capable of holding a semiconductor wafer on a fixed-side surface plate without wax bonding and subjecting the wafer surface to mechanical and chemical polishing. The present invention relates to a less-mount type polishing apparatus, and more particularly to an improvement of a back pad thereof.

[0002]

2. Description of the Related Art As a kind of polishing apparatus for a semiconductor wafer, particularly a silicon wafer, a waxless mount type polishing apparatus has been conventionally known. As shown in FIG. 4, this apparatus comprises a lower platen (polishing side platen) 104 having an upper surface on which a polishing cloth 105 is stretched, and an upper platen (fixed surface) having a lower surface provided with a guide ring 102 for fixing a wafer. A back pad 103 made of a relatively soft nonwoven fabric having a water retention property inside a guide ring 102.
It is what was held. At the time of polishing the surface of the silicon wafer 100, pure water or the like is supplied to the back pad 103, and the silicon wafer 100 is held from the back side by the surface tension. At this time, the silicon wafer 100 is held such that the polished surface (surface) protrudes from the lower edge of the guide ring 102. 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. .

[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 having a uniform thickness and a non-uniform hardness, 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.

Accordingly, as shown in FIG. 4, 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 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 Accordingly, an object of the present invention is to provide a waxless mount type polishing apparatus capable of preventing unevenness in thickness of a semiconductor wafer due to collapse of an outer peripheral portion of a back pad during surface polishing. That is the purpose.

[0006]

According to a first aspect of the present invention, there is provided a polishing-side platen on which a polishing cloth is spread on a surface, and a polishing-side platen disposed opposite to the polishing-side platen for fixing a wafer on the surface. A fixed-side platen provided with a guide ring, and a waxless mount-type polishing apparatus in which a back pad that retains a semiconductor wafer by water surface tension with water retention is stored inside the guide ring. In the above, the back pad is a waxless mount type polishing apparatus made of a synthetic resin sheet.

According to a second aspect of the present invention, there is provided the waxless mount type polishing apparatus according to the first aspect, wherein the back pad has a large number of water retention holes.

In this waxless mount type polishing apparatus, the polishing-side surface plate may be a lower surface plate and the fixed-side surface plate may be an upper surface plate, or may be arranged upside down.
The back pad made of a synthetic resin sheet may or may not have a water retention hole. In short, it is only necessary that the semiconductor wafer can be rotatably held on the synthetic resin back pad during polishing. The diameter of the water retention hole when formed is, for example, 1000 μm or less. If it exceeds 1000 μm, the shape of the water retention hole is transferred to the wafer, that is, the shape is poor. In the case where the back pad is not provided, a material of the back pad includes, for example, a fluororesin (trade name “Teflon”) which easily repels water. Of these, fluororesins are particularly preferred because of their low friction coefficient. Further, the thickness of the back pad is preferably 3 mm or less. Processing is possible even if it exceeds 3 mm, but if it exceeds 3 mm, the material price becomes expensive and the feasibility becomes difficult.

[0009]

According to the first and second aspects of the present invention, when polishing the wafer surface, pure water or the like is supplied to a back pad which is made of a synthetic resin sheet in advance and is surrounded by a guide ring. Water is put on the surface of the back pad. Thereafter, the semiconductor wafer is housed in the guide ring such that the polished surface of the wafer projects slightly outward from the periphery of the guide ring. As a result, the semiconductor wafer is adsorbed and held on the back pad by the surface tension of the stretched water. Next, 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, the semiconductor wafer is supported by the back pad in the guide ring by the water stretched on the surface of the back pad, and rotates independently of the rotation of the polishing head (upper platen) independently. . As a result, the surface of the semiconductor wafer does not sag at the outer peripheral portion. In addition, the back pad has a relatively small amount of deformation during polishing of the semiconductor wafer, in combination with the effect that the stretched water serves as a cushion and the material is a synthetic resin sheet. On the other hand, an appropriate elastic holding force can be provided. At the same time, the shape retention from the back surface side of the wafer by the back pad, particularly the shape retention at the outer peripheral portion of the back pad is improved.

Therefore, 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 during this surface polishing, Due to the influence of water and the like, the outer peripheral portion of the back pad is not easily crushed. No sinking occurs at the outer periphery of the back pad. As described above, the outer peripheral portion of the semiconductor wafer during surface polishing is maintained in shape from the back side by the back pad having a relatively small amount of deformation.
The semiconductor wafer after polishing can have a small thickness unevenness in which the thickness of the central part and the peripheral part thereof are substantially equal.

In particular, according to the second aspect of the present invention, the pure water or the like supplied to the back pad is retained in the water retaining hole in advance, and then the semiconductor wafer is accommodated in the guide ring. The semiconductor wafer is adsorbed and held by a relatively large amount of water in each water holding hole. Thereby, the asynchronous state with the rotation of the polishing head (upper platen) is improved, and independent rotation is facilitated. As a result, surface drooping of the outer peripheral portion of the semiconductor wafer is less likely to occur. Also, during this 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 water retained by the cushion does not affect the cushion. Since it plays a role, the outer peripheral portion of the back pad is not easily crushed.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. First, a waxless mount type polishing apparatus 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 of the present invention.
FIG. 3 is a front view showing a state in which the surface of the silicon wafer according to one embodiment of the present invention is being polished.

In FIG. 1, reference numeral 10 denotes a wax-less mount type polishing apparatus according to one embodiment. The wax-less mount type polishing apparatus 10 comprises a lower platen 13 and an upper platen arranged opposite thereto. 15 is provided. In a lower surface plate 13 which is an example of a polishing-side surface plate, a polishing cloth 12 is spread on an upper surface of the lower surface plate 13 via a sponge rubber 11 of a thick material. The sponge rubber 11 is not always required. An upper stool 15 which is an example of a fixed stool has a guide ring 14 for fixing a wafer on a lower surface thereof. The lower surface plate 13 and the upper surface plate 15 are both disk-shaped, and their opposing surfaces are flat. The lower platen 13 and the upper platen 15 are configured to be rotatable around an axis by driving means (not shown) via rotating shafts 16 and 17. In addition,
The upper surface plate 15 is configured to be able to move up and down by raising and lowering the rotating shaft 17.

Inside the guide ring 14 which is a circular ring, a back pad 18 is housed and held with its upper surface in contact with the lower surface of the upper stool 15. As shown in FIGS. 2 and 3, the back pad 18 is made of a Teflon sheet as an example of a synthetic resin sheet, and has a thickness of 80%.
0 μm, and has a predetermined elastic force (flexibility) in the thickness direction as a whole. A large number of water retention holes 18a each having a diameter of about 500 μm are formed in the back pad 18 so as to penetrate the front and back surfaces. Note that the silicon wafer 19 is a CZ wafer and has a thickness of 630 μm.

Next, a description will be given of a waxless polishing method for the silicon wafer 19 using the waxless mount type polishing apparatus 10 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 attached, and pure water or the like is supplied to the back pad 18 held by the guide ring 14. Pure water is held in a large number of water retention holes 18a. After that, the silicon wafer 19 is accommodated in the guide ring 14. At this time, the wafer is set so that the wafer polishing surface is located below the lower end surface of the guide ring 14. Thereby, the water retention hole 1
The silicon wafer 19 is adsorbed and held on the back pad 18 by the surface tension of the water held in 8a. Thereafter, the upper platen 15 is rotated and revolved on the lower platen 13 while supplying an abrasive containing abrasive particles having a normal particle size, and the polished surface of the silicon wafer 19 is polished with the polishing pad 12.

At this time, the silicon wafer 19 rotates independently of the polishing head 15. Further, since the back pad 18 sufficiently retains water in the water retaining holes 18a on the surface thereof, this water serves as a cushion, and since the back pad 18 is a Teflon sheet having a moderate hardness and flexibility, An appropriate cushioning property of the silicon wafer 19 at the time of surface polishing can be sufficiently ensured. At the same time, the shape retention of the back pad 18, particularly the shape retention at the outer periphery of the pad, is good. As a result of these,
During this surface polishing, 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 18 whose movement is restricted by the guide ring 14, The part is not easily 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 18 which can reduce the amount of deformation via water. And a silicon wafer having a small thickness unevenness, in which the thickness of the outer peripheral portion is substantially equal. In the above embodiment, a back pad having a large number of water retention holes is used, but a back pad having no water retention holes may be used. However, when the water holding amount is small, synchronization with the upper surface plate is likely to occur.

[0019]

As described above, according to the waxless mount type polishing apparatus of the present invention, the back pad is made of synthetic resin, and the semiconductor wafer being polished is rotatably held. In this case, it is possible to prevent the occurrence of unevenness in the thickness of the semiconductor wafer caused by the collapse of the outer peripheral portion of the back pad and the sagging.

[Brief description of the drawings]

FIG. 1 is a front 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 front view showing a surface polishing state of the silicon wafer according to one embodiment of the present invention.

FIG. 4 is a front view showing a state during polishing of a wafer surface of a conventional waxless mount type polishing apparatus.

[Explanation of symbols]

 Reference Signs List 10 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), 18 back pad, 18a water retention hole, 19 silicon wafer (semiconductor) Wafer).

Claims (2)

[Claims] 1. 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 water retention and holding a semiconductor wafer by surface tension of water is stored inside the guide ring, the back pad is made of a synthetic resin sheet. Waxless mount type polishing machine. 2. The polishing apparatus according to claim 1, wherein the back pad has a plurality of water retention holes.