Abrading – Machine – Combined
Reexamination Certificate
1998-09-04
2001-07-17
Eley, Timothy V. (Department: 3723)
Abrading
Machine
Combined
C451S043000, C451S209000, C451S210000, C451S254000, C451S362000
Reexamination Certificate
active
06261160
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus for the specular polishing of the chamfered outer circumference edges of a semiconductor wafer, a magnetic disc substrate, an optical-disc substrate, or other characteristically disc-shaped work.
PRIOR ART
As an example, a semiconductor wafer such as a silicon wafer generally has its periphery chamfered to prevent the chipping of its edge and crown during epitaxial growth. The chamfering is done by polishing the wafer with a diamond grindstone. However, this polishing often leaves a process-distorted layer, which may produce a crystal defect during repeated thermal treatment in a device process.
The process-distorted layer is customarily removed by etching, but etched surfaces tend to demonstrate a wavy or scale-like pattern, with projecting and recessed areas susceptible to staining. Such stains may be dispersed over the entire wafer during the device process, degrading the characteristics of the device.
A relatively new technique for specular polishing has recently been established as a way of polishing a chamfered wafer edge. The technique takes an approach that departs significantly from wafer-surface polishing techniques. This applicant has also proposed a technique for polishing edges, disclosed, for example, in Japanese Patent Application Laid Open No. 1-71656. This polishing technique rotates a wafer having a chamfered edge on its circumferential surface while pressing its circumferential edge against a working surface on the outer circumference of a rotating polishing drum. This method enables simple and reliable polishing of the wafer edge, resolving the problems associated with chamfering.
However, a polishing apparatus of this kind contacts a wafer at one point with one polishing drum, an arrangement that limits processing efficiency and requires a relatively long time for processing. Currently, this inefficiency can be reduced somewhat by increasing the diameter of the polishing drum, which in turn increases its contact area upon the wafer and thus reduces processing time.
However, for this method of externally contacting a circular wafer with a cylindrical polishing drum, the degree to which the contact area can be increased and polishing time reduced is limited. Increasing the diameter of the polishing drum also increases the required installation space and the size of the apparatus. Trends are soon expected to bring a demand for larger wafers with diameters of 30 to 40 cm, which would require even larger polishing apparatuses.
DISCLOSURE OF THE INVENTION
A main object of this invention is to provide a polishing apparatus having high processing efficiency, capable of simultaneously specularly polishing the circumferential edges of a work at a number of points.
Another object of this invention is to provide a productive polishing apparatus capable of simultaneously and continuously specularly polishing the circumferential edges of a number of works.
To achieve these objectives, this invention provides a specular-polishing apparatus having, on a rotating table intermittently rotating from a handling position to a front-plane-side edge processing position to a rear-plane-side edge processing position, a number of polishing drums for simultaneously specularly polishing the circumferential edges of a work at a number of points and a number of work-holding means for holding a disc-shaped work having chamfered circumferential edges on its front and rear planes to allow the polishing drums to contact the edges of the work.
In a polishing apparatus of this configuration, when a handling means supplies an unprocessed work to the work-holding means at the handling position, the rotating table rotates through a specified angle to move the work-holding means to the front-plane-side edge processing position. At this position, the front-plane-side edge is simultaneously pressed against the polishing drums.
Once the front-plane-side edge of the work has been polished, a work-inverting means turns the work upside down and the rotating table rotates to move the work-holding means to a rear-plane-side edge processing position. At this position, the rear-plane-side edge of the work is pressed against the rotating polishing drums for specular polishing.
Once the rear-plane-side edge of the work has been polished, the rotating table rotates to return the work-holding means to the handling position, where the handling means unloads the processed work and supplies an unprocessed work. This process is then repeated for specular polishing of the edges of an unprocessed work.
Thus, according to this invention, the circumferential edges of the work are contacted simultaneously by a number of polishing drums and specularly polished at a number of points, thereby improving processing efficiency and reducing the time required for processing. In addition, a number of work-holding means can simultaneously and continuously process a number of works, thereby improving productivity.
According to a specific embodiment of this invention, the specular-polishing apparatus has three polishing drums and three work-holding means, wherein each work-holding means is disposed at a position intermediate between two adjacent polishing drums so as to move in the radial direction of the rotating table.
According to a preferable embodiment of this invention, the work-holding means has a pressing means for setting the pressure used to polish a work and an alignment mechanism for even contact of the work with the two polishing drums.
The pressing means consists of a weight hanging from the work-holding means, and the alignment mechanism is composed of a slide member and a rail supporting the work-holding means in such a way that the means can be moved in a direction parallel to a line joining the centers of the two polishing drums.
According to this invention, the alignment mechanism preferably has a means for absorbing the force resulting from the contact between the two polishing drums and the work to displace the work-holding means to one of the polishing drums, using an impelling force opposed to the initial force.
Ideally, the polishing drums and the work-holding means can be moved relative to the axial direction of the polishing drums to vary the position in which the work contacts the drums.
REFERENCES:
patent: 5097630 (1992-03-01), Maeda et al.
patent: 5117590 (1992-06-01), Kudo et al.
patent: 5514025 (1996-05-01), Hasegawa et al.
patent: 5547415 (1996-08-01), Hasegawa et al.
patent: 5658189 (1997-08-01), Kagamida
patent: 5674110 (1997-10-01), Cuoghi
patent: 5816897 (1998-10-01), Raeder et al.
patent: 64-71656 (1989-03-01), None
Eley Timothy V.
Snell & Wilmer L.L.P.
Speedfam Co., Ltd.
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