Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
1999-03-15
2001-04-17
Rose, Robert A. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S398000
Reexamination Certificate
active
06217417
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for polishing a thin plate, for example, a semiconductor wafer, a wafer made of quartz, ceramic material or the like, and to a holding plate for holding the thin plate, which is used during polishing.
2. Description of Related Art
Conventionally, polishing for a thin plate is carried out by giving a relative motion between the thin plate to be polished and a polishing cloth, i.e., polishing pad, while holding the thin plate on a holding plate and pressing the thin plate against the polishing pad by loading the holding plate from a polishing head, with supplying a polishing slurry between the thin plate and the polishing pad.
As the holding plate for holding a thin plate, one made of glass or ceramic Is generally used. However, one made of glass is relatively easy to bend when it is loaded from the polishing head. Because of the effect of bending, the peripheral portion of the thin plate tends to be pressed more strongly against the polishing pad, so that the peripheral portion may be polished more than the central portion thereof. As a result, there is a problem that the flatness of the polished surface of the thin plate is inferior to that of a ceramic plate because of non-uniform polishing in the surface of the thin plate. Therefore, when a high flatness is required, a ceramic plate is generally used as the holding plate.
Although the ceramic holding plate is manufactured through steps of forming and sintering, it is difficult to obtain a ceramic holding plate with precise dimensions for front and back surfaces by only such steps. Generally, in order to obtain precise dimensions therefor, a mechanical processing is performed on the peripheral, front and back surfaces of the plate after the forming and sintering. As the mechanical processing, lapping using a bonded diamond grinding wheel is performed. During lapping, a predetermined abrasive slurry is supplied, and after the lapping, an acid cleaning using an acid aqueous solution containing hydrochloric acid or the like, and a pure water cleaning are carried out for washing the abrasive slurry away.
When a polishing has been carried out with a ceramic holding plate which was made in the above-described manner, it has been ascertained that the following problem often occurs.
That is, when a polishing is carried out to thin plates by using a ceramic holding plate, in batch processing, it has been ascertained that there is a high probability that scratches due to polishing and the like are formed in the polished surfaces of all thin plates and that scratches, dents or stains are formed on the back surfaces of the thin plates. Because the existence of such scratches, dents or the like lead to an extreme drop of the rate of acceptable products, an urgent countermeasure thereto is desired.
SUMMARY OF THE INVENTION
The present Invention was developed In view of these problems.
An object of the present invention is to provide a polishing method which is effective for improvement in throughput of the thin plates.
Another object of the present invention is to provide a holding plate for holding a thin plate thereon, which is effective for improvement in throughput of the thin plates.
The inventors of the present invention conducted a variety of experiments to research the cause of lowering in throughput of the thin plates. As a result, the following has been found.
First, the scratches on the front surface of the thin plate due to polishing and the scratches, dents or stains on the back surface are caused by the abrasive grains from the bonded diamond wheel and the ceramic dusts. Second, the scratches due to polishing are mainly caused by the abrasive grains from the bonded diamond wheel and the ceramic dusts, which are attached to the back surface of a holding plate for holding the thin plate. Third, the scratches or stains on the back surface of the thin plate are caused by the abrasive grains from the bonded diamond wheel and the ceramic dusts, which are attached to the front surface of the holding plate.
That is, during lapping the holding plate by a bonded diamond wheel, abrasive grains are separated down from the bonded diamond wheel to attach to the front and back surfaces of the holding plate. The attached abrasive grains on the front and back surfaces of the holding plate are hard to separate therefrom even by the following acid cleaning and pure water cleaning. As a result, after the following steps of acid cleaning and pure water cleaning, a lot of attached abrasive grains are left thereon. On the surface of the lapped holding plate, there are fine irregularities. The fine irregularities contribute to creation of dusts. When the abrasive grains or ceramic dusts on the holding plate are separated to fall on the polishing pad before or during polishing, the surface to be polished, of the thin plate is scratched by the fallen abrasive grains or ceramic dusts during the polishing step. When abrasive grains are left on the front surface of the holding plate or ceramic dusts are attached thereto, and a thin plate is adhered to the holding plate through wax, in the region in which the abrasive grains or the dusts are left, scratches are created on the back surface of the thin film or stains are induced on the back surface, during the polishing step.
The present invention was made on the basis of the above-described knowledge.
In accordance with one aspect of the present invention, the method for polishing a thin plate comprises the steps of: holding the thin plate on a front surface of a holding plate, wherein the holding plate is made of ceramic and the front surface thereof to hold the thin plate thereon has been polished; and carrying out a relative motion between the thin plate and a polishing pad while pressing the thin plate against the polishing pad with supplying a polishing slurry between them. The material for the holding plate can be selected from various types of ceramic, e.g., alumina, silicon carbide, silicon nitride, and the like.
According to the method for polishing a thin plate, the previous polishing for the front surface of the holding plate can clear the abrasive grains separated from the bonded diamond wheel and the ceramic dusts, away from the front surface of the holding plate and can make the front surface of the holding plate smooth. Accordingly, because polishing for the thin plate is carried out without abrasive grains from the bonded diamond wheel nor ceramic dusts, on the front surface of the holding plate, it is possible to effectively prevent the occurrence of scratches due to polishing on the front surface of the thin plate, caused by the abrasive grains and ceramic dusts separated from the front surface of the holding plate, and the occurrence of scratches or stains on the back surface of the thin plate, caused by the abrasive grains and the dusts which are attached to the front surface of the holding plate.
Preferably, the holding plate further has a back surface which has been polished.
According to the method for polishing a thin plate, the previous polishing for the back surface of the holding plate can clear the abrasive grains separated from the bonded diamond wheel and the ceramic dusts, away from the back surface of the holding plate and can make the back surface of the holding plate smooth. Accordingly, because polishing for the thin plate is carried out without abrasive grains from the bonded diamond wheel nor ceramic dusts, on the back surface of the holding plate, it is possible to effectively prevent the occurrence of scratches due to polishing on the front surface of the thin plate, caused by the abrasive grains and dusts separated from the back surface of the holding plate.
Preferably, the holding plate further has a peripheral surface which has been polished.
According to the method for polishing a thin plate, the previous polishing for the back surface of the holding plate can clear the abrasive grains separated from the bonded diamond wheel and the ceramic dusts, away from the periphe
Kida Takahiro
Nakamura Mikio
Oliff & Berridg,e PLC
Rose Robert A.
Shin-Etsu Handotai & Co., Ltd.
LandOfFree
Method for polishing thin plate and plate for holding thin... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for polishing thin plate and plate for holding thin..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for polishing thin plate and plate for holding thin... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2478370