JP2008060598A - Method of waxless mount type polishing and device thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of waxless mount type polishing and device thereof which hardly lowers a holding force of a semiconductor wafer by a water-retained back pad and prevents peripheral sagging of the semiconductor wafer with ease at low cost. <P>SOLUTION: A central back pad 16A is integrally formed at the front side at the center of the back pad 15 having the same material as the back pad 15 and being almost round shape. In a hole part of a template 14, the center of the back pad 15 is made to project by a predetermined height "d" over its periphery toward a polishing cloth 13. Under these circumstances, a semiconductor wafer W is polished. As a result, while hardly lowering a holding force of the semiconductor wafer W by the back pad 15 in a water retention state and the central back pad 16A, peripheral sagging of the semiconductor wafer W can be prevented with ease at low cost. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a waxless mount type polishing method and apparatus, and more particularly to a waxless mount type polishing technique for performing mechanical chemical polishing on the surface of a semiconductor wafer held in a waxless manner.

Conventionally, a waxless mount type polishing method is known as a kind of polishing method for silicon wafers. As shown in FIG. 5, the waxless mount type polishing apparatus used in this method is a polishing head having a polishing surface plate 104 with a polishing cloth 105 stretched on the upper surface and a wafer fixing template 102 on the lower surface. 101. The template 102 is provided on the lower surface of the polishing head 101 via a non-woven back pad 103 having water retention.
At the time of polishing, pure water is supplied to the back pad 103, and the silicon wafer W accommodated in the hole of the template 102 is held from the back side by the surface tension. At this time, the silicon wafer W protrudes downward from the end face of the template 102 by a predetermined height over the entire polishing surface.
Then, the polishing surface of the silicon wafer W is mirror-polished by rotating the polishing head 101 on the polishing surface plate 104 while supplying an abrasive containing free abrasive grains to the polishing surface of the polishing cloth 105.

However, such conventional waxless mount type polishing has the following disadvantages.
That is, since the back pad 103 is made of a soft non-woven fabric, the shape retention at the outer peripheral portion of the back pad 103 has been reduced.
Specifically, surface pressure acts on the silicon wafer W during polishing from the polishing head 101 side. Also, external force due to rotation and revolution is added. The surface pressure of the polishing head 101 is not uniform across the entire surface microscopically.

It is an object of the present invention to provide a waxless mount type polishing method and apparatus capable of preventing the peripheral sagging of a semiconductor wafer easily and at low cost without substantially reducing the holding power of the semiconductor wafer by the back pad that has retained water. And that is the purpose.
Furthermore, the present invention provides a waxless mount type polishing method and apparatus that can be changed to a polishing apparatus having the effects of the present invention simply and at low cost even with an existing polishing apparatus. It is aimed.

The invention according to claim 1 is a waxless mount type in which a semiconductor wafer is accommodated in a hole inside an annular template, and a semiconductor wafer is polished by interposing a back pad between the semiconductor wafer and a polishing head. In the polishing method, a substantially circular central portion back pad made of the same material as the back pad is integrally formed on the front side of the central portion of the back pad, and the central portion of the back pad is formed in the hole of the template. Waxless mount polishing method for polishing a semiconductor wafer by holding the central portion of the semiconductor wafer in a state of protruding from the outer peripheral portion by a predetermined height toward the polishing cloth by increasing the thickness from the outer peripheral portion. It is.
The polishing cloth is spread on the surface facing the polishing head among the exposed surfaces of the polishing surface plate. Examples of the polishing cloth include a hard urethane pad and a CeO ₂ pad.
As an abrasive | polishing agent, what mixed baked silica, colloidal silica (abrasive grain), an amine (processing accelerator), an organic polymer (haze inhibitor), etc. can be employ | adopted, for example. Colloidal silica is a transparent or opaque milky white colloidal solution dispersed in water as primary particles without aggregation of silicic acid fine particles.

As the semiconductor wafer, various wafers such as a gallium arsenide wafer can be adopted in addition to a typical silicon wafer.
The polishing head may be a single wafer type in which one semiconductor wafer is held on the surface facing the polishing surface plate, or a batch type in which a large number of semiconductor wafers are held together. The polishing head may be reciprocated along the surface of the polishing pad or may be non-reciprocal. When reciprocating, a part of the outer peripheral portion of the semiconductor wafer may be protruded outside the polishing cloth and may or may not be polished. The number of polishing heads used is not limited. There may be one or more.
The polishing head is normally disposed opposite to the upper surface of the polishing platen, but it may be upside down. Further, it may be a vertical polishing apparatus in which the axial directions of the polishing head and the polishing surface plate are horizontal.

The template has a hole inside the plate that is slightly larger than the diameter of the semiconductor wafer. A semiconductor wafer is accommodated in this hole. The height of this template is not limited. However, a height that is substantially the same as the thickness of the semiconductor wafer or a height at which the semiconductor wafer protrudes by 1 to 200 μm is preferable.
The material of this template is not limited. For example, a glass epoxy resin, various ceramics, etc. are mentioned.
The material of the back pad (including the thick part) is not limited. For example, a non-woven fabric such as a suede cloth can be used. Moreover, the hardness is not limited.
The thickness of the back pad is not limited. However, 2 mm or less is preferable. If it exceeds 2 mm, hardness unevenness tends to occur on the back pad.

The method of thickening the center part of the back pad from the outer peripheral part in the hole of the template is not limited. For example, the central portion of the back pad may be integrally formed thick in the hole of the template.
The thickness of the thickened central portion of the back pad is not limited. However, a thickness at which the central portion of the semiconductor wafer protrudes 1 to 200 μm from the outermost peripheral portion of the semiconductor wafer is preferable.

  The material of the central back pad is the same material as the back pad.

  The invention according to claim 2 is a waxless mount type in which a semiconductor wafer is accommodated in a hole inside an annular template, and a semiconductor wafer is polished by interposing a back pad between the semiconductor wafer and a polishing head. In the polishing apparatus, by increasing the thickness of the central portion of the back pad, a central thick portion that projects the central portion of the semiconductor wafer from the outer peripheral portion toward the polishing cloth by a predetermined height is formed at the center of the semiconductor wafer. The central thick portion is a substantially circular central partial back pad integrally formed of the same material as the back pad on the surface of the central portion of the back pad. This is a waxless mount type polishing apparatus.

The invention according to claim 3 is the waxless mount type polishing apparatus according to claim 2, wherein the central back pad has a thickness of 200 μm or less, and the diameter of the central back pad is 2 mm or more smaller than the diameter of the semiconductor wafer. is there.
When the thickness of the thick portion of the central back pad exceeds 200 μm, the amount by which the central portion of the semiconductor wafer protrudes from the outer peripheral portion of the wafer increases. Therefore, the amount of polishing at the center of the semiconductor wafer increases, and there is a risk that the semiconductor wafer slightly stands on the outer periphery.
Furthermore, when the difference between the diameter of the central back pad and the diameter of the semiconductor wafer is less than 2 mm, the outer peripheral portion of the semiconductor wafer may be polished too much.

According to the first and second aspects of the present invention, the semiconductor wafer is adsorbed by the surface tension of water to the back pad in the hole of the template and subjected to normal polishing. At this time, since the central portion of the semiconductor wafer protrudes toward the polishing cloth from the outer peripheral portion by the thick portion of the back pad, during polishing, the wafer central portion is a unit of the polishing cloth compared to the outer peripheral portion. The contact area per time and the pressure per unit time increase. As a result, the peripheral sag of the semiconductor wafer can be easily and inexpensively prevented without substantially reducing the holding power of the semiconductor wafer by the back pad that has retained water. As a result, a semiconductor wafer with high flatness can be obtained. Therefore, for example, when an SOI wafer is manufactured, it is possible to prevent the generation of voids due to the peripheral sag.
Then, a substantially circular central partial back pad integrally formed of the same material as the back pad is disposed on the front side of the central portion of the back pad in the hole portion of the template. As a result, the central portion of the semiconductor wafer protrudes toward the polishing cloth higher than the outer peripheral portion by a predetermined height. As a result, even an existing polishing apparatus can be changed to a polishing apparatus capable of obtaining the effects of the present invention in which the central portion of the back pad is thickened easily and at low cost.

According to the first and second aspects of the present invention, the central portion of the back pad is thickened from the outer peripheral portion in the hole portion of the template, and the central portion of the semiconductor wafer is predetermined from the outer peripheral portion toward the polishing cloth. Since it protrudes only by the height, the holding force of the semiconductor wafer by the water-retained back pad is hardly reduced, and it is possible to easily prevent the outer circumference of the semiconductor wafer from being lowered at a low cost. Thereby, a semiconductor wafer with high flatness can be produced. For example, when a bonded wafer is manufactured, voids can be prevented from occurring at the bonded interface between the semiconductor wafer and the semiconductor wafer due to the peripheral sag.
And, in the hole portion of the template, the central portion of the semiconductor wafer is arranged on the front side of the central portion of the back pad by arranging a substantially circular central portion back pad integrally formed of the same material as the back pad, so that the central portion of the semiconductor wafer is the outer peripheral portion. It protrudes toward the polishing cloth higher than the predetermined height. Thereby, even if it is an existing polisher, it can change to the polisher which can obtain the effect of this invention which made the center part of the back pad thick by simple and low cost.

  Hereinafter, reference examples of the present invention will be described.

FIG. 1 is a longitudinal sectional view of a waxless mount type polishing apparatus according to a reference example of the present invention. FIG. 2 is a perspective view of a back pad according to a reference example of the present invention.
In FIG. 1, reference numeral 10 denotes a waxless mount type polishing apparatus according to a reference example of the present invention. The polishing apparatus 10 includes a polishing surface plate 11 and a polishing head 12 disposed above and facing the polishing platen 11. A polishing cloth 13 is stretched on the upper surface of the polishing surface plate 11 via a thick sponge rubber. The polishing head 12 is provided with a wafer fixing template 14 on the lower surface thereof.

The polishing surface plate 11 and the polishing head 12 are disk-shaped, and the opposing surfaces are flat surfaces. The polishing surface plate 11 and the polishing head 12 are rotated by rotating means (not shown) around the respective rotation axes. The polishing head 12 moves up and down by raising and lowering the rotation shaft.
The template 14 is a circular ring-shaped glass epoxy plate. The template 14 is provided on the lower surface of the polishing head 12 via a back pad 15 attached to the lower surface of the polishing head 12. The thickness of the template 14 is substantially the same as that of the silicon wafer W.
As shown in FIGS. 1 and 2, the back pad 15 is made of suede, and the thickness is uniform throughout the pad. The silicon wafer W to be polished is a CZ wafer.

The feature of this reference example is that an annular outer peripheral portion back pad 16 is arranged on the front side of the outer peripheral portion of the back pad 15 in the hole portion of the template 14, and the outer peripheral portion of the silicon wafer W is more than the central portion of the silicon wafer W. It is a point which polishes by projecting only predetermined height toward the downward direction.
The outer peripheral portion back pad 16 thickens only the outer peripheral portion of the back pad 15 and is a suede pad having a ring shape with a thickness of 200 μm or less and a radial width of 5 mm or less. When the outer peripheral portion back pad 16 is attached to the lower surface of the back pad 15 along the inner periphery of the template 14, the outer peripheral portion of the silicon wafer W protrudes outward from the outer edge surface of the template 14 by a height d during polishing. To do.

Next, a waxless mount polishing method for the silicon wafer W using the waxless mount polishing apparatus 10 according to this reference example will be described.
As shown in FIG. 1, when polishing the silicon wafer W, the template 14 and the outer peripheral portion back pad 16 are respectively mounted at predetermined positions, and a predetermined amount of pure water or the like is supplied to the back pad 15 and the outer peripheral portion back pad 16. . Thereafter, the silicon wafer W is accommodated in the template 14. Thereby, the back surface of the silicon wafer W is adsorbed and held on the back pad 15 by the surface tension of water. At this time, the outer peripheral portion of the silicon wafer W is attracted and held by the outer peripheral portion back pad 16.
As a result, the surface (polished surface) of the central portion of the silicon wafer W becomes substantially the same height as the lower edge surface of the template 14, while the surface of the outermost peripheral portion of the silicon wafer W has a height d higher than the central portion of the wafer. Only protrudes downwards.
Thereafter, the polishing head 12 is rotated and revolved on the polishing surface plate 11 while supplying an abrasive containing abrasive grains, and the surface of the silicon wafer W is polished by the polishing cloth 13.

Since such polishing is performed, the contact area per unit time with the polishing cloth 13 and the pressure per unit area are larger in the outer peripheral portion of the silicon wafer W than in the central portion. As a result, the polishing amount of the outer peripheral portion of the silicon wafer W is increased from that of the central portion. Therefore, even if the shape of the back surface of the outer peripheral portion of the etched wafer before polishing is sagging, when the silicon wafer W is peeled off from the back pad 15 after polishing, the outer peripheral standing of the silicon wafer W is transferred by the sagging transfer to the wafer surface. The surface of the outer peripheral portion of the silicon wafer W is polished in advance by the amount. Thereby, the peripheral standing of the silicon wafer W is prevented, and the flatness of the surface of the silicon wafer W is improved. As a result, for example, when an SOI wafer is manufactured, it is possible to prevent the generation of voids at the bonding interface between the active layer wafer and the support substrate wafer due to the standing of the outer periphery.
Moreover, in this reference example, the outer peripheral portion back pad 16, which is a separate body from the back pad 15, is attached to the front side of the back pad 15 in the hole of the template 14. Therefore, even an existing polishing apparatus can be changed to a polishing apparatus having the above-described effects easily and at low cost.

Next, based on FIG. 3 and FIG. 4, the Example of this invention is described.
FIG. 3 is a longitudinal sectional view of a waxless mount type polishing apparatus according to an embodiment of the present invention. FIG. 4 is a perspective view of the back pad according to the embodiment of the present invention.
As shown in FIGS. 3 and 4, the feature of the waxless mount type polishing apparatus 20 of this embodiment is that a substantially circular center is provided on the front side of the center portion of the back pad 15 instead of the outer peripheral portion back pad 16 of the reference example. The partial back pad 16A is disposed. Thereby, the polishing amount of the center part of the silicon wafer W becomes larger than the outer peripheral part of the wafer.

The central back pad 16A thickens only the central part of the back pad 15, and is a substantially circular pad having a thickness of 200 μm or less and a diameter of 2 mm or more smaller than the diameter of the silicon wafer W. By sticking the central back pad 16A to the lower surface of the central portion of the back pad 15, the central portion of the silicon wafer W protrudes outward from the outer edge surface of the template 14 by a height d during polishing. Thereby, the contact area per unit time with the polishing pad 13 and the pressure per unit area are larger in the wafer center than in the outer periphery. As a result, the occurrence of sagging of the outer periphery of the silicon wafer W can be easily and inexpensively prevented without substantially reducing the holding force of the silicon wafer W by the back pad 15 that has retained water. As a result, a silicon wafer W with high flatness can be obtained. Therefore, for example, when an SOI wafer is manufactured, it is possible to prevent the occurrence of voids at the bonding interface between the active layer wafer and the support substrate wafer due to the peripheral sag.
In addition, since the substantially circular central portion back pad 16A is disposed in the central portion of the back pad 15 in the hole portion of the template 14, even with an existing polishing apparatus, the center of the back pad 15 can be easily and at low cost. It is possible to change to a polishing apparatus in which the effect of the present invention is obtained with a thick part.
Other configurations, operations, and effects are substantially the same as those in the reference example, and thus description thereof is omitted.

It is a longitudinal cross-sectional view of the waxless mount type polishing apparatus according to the reference example of the present invention. It is a perspective view of the back pad concerning the reference example of this invention. 1 is a longitudinal sectional view of a waxless mount type polishing apparatus according to an embodiment of the present invention. It is a perspective view of the back pad concerning the example of this invention. It is a longitudinal cross-sectional view which shows the state during grinding | polishing of the grinding | polishing apparatus to which the waxless mount type grinding | polishing method which concerns on the conventional means was applied.

Explanation of symbols

10, 20 Waxless mount type polishing equipment,
12 polishing head,
13 Abrasive cloth,
14 templates,
15 Back pad,
16A center part back pad,
W Silicon wafer (semiconductor wafer).

Claims (3)

In a waxless mount type polishing method in which a semiconductor wafer is accommodated in a hole inside an annular template and a semiconductor wafer is polished by interposing a back pad between the semiconductor wafer and a polishing head.
A substantially circular central part back pad made of the same material as the back pad is integrally formed on the front side of the central part of the back pad, and the central part of the back pad is thicker than the outer peripheral part in the hole of the template. A waxless mount polishing method in which the semiconductor wafer is polished by holding the semiconductor wafer in a state where the central portion of the semiconductor wafer protrudes from the outer peripheral portion toward the polishing cloth by a predetermined height by being thickened. In the waxless mount type polishing apparatus for polishing the semiconductor wafer by accommodating the semiconductor wafer in the hole inside the annular template and interposing the back pad between the semiconductor wafer and the polishing head,
By increasing the thickness of the central portion of the back pad, the central thick portion for projecting the central portion of the semiconductor wafer from the outer peripheral portion thereof toward the polishing cloth by a predetermined height is formed between the central portion of the semiconductor wafer and the back pad. Between
The central thick portion is a waxless mount type polishing apparatus which is a substantially circular central partial back pad integrally formed with the same material as the back pad on the surface of the central portion of the back pad.   3. The waxless mount type polishing apparatus according to claim 2, wherein the central partial back pad has a thickness of 200 [mu] m or less, and the diameter of the central partial back pad is 2 mm or more smaller than the diameter of the semiconductor wafer.

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