Method and apparatus for wafer chamfer polishing

Details Method and apparatus for wafer chamfer polishing Method and apparatus for wafer chamfer polishing

1996-03-20

2001-05-22

Rose, Robert A. (Department: 3723)

Abrading

Abrading process

Glass or stone abrading

C451S180000, C451S541000

Reexamination Certificate

active

06234879

ABSTRACT:

This application is related to a copending patent application titled “A WAFER CHAMFER POLISHING APPARATUS WITH ROTARY CIRCULAR DIVIDING TABLE” for which foreign priority benefits are claimed on the basis of Japanese Utility Model Application No. 4-50005 filed on Jul. 16, 1992. Said copending application is commonly assigned with the present application.
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus for polishing the chamfers made along the periphery of a semiconductor wafer.
DESCRIPTION OF THE PRIOR ART
FIG.
8
and
FIG. 9
show a conventional wafer chamfer polishing apparatus.
FIG. 8
is a top plan view of the wafer chamfer polishing apparatus, and
FIG. 9
is a view seen in the direction of arrow H of FIG.
8
. In this wafer chamfer polishing apparatus, the wafers W, which are taken out from a cassette
101
one by one, are transported to an OF (orientation flat) orientating assembly
103
by means of a conveyor
102
. At this OF orientating assembly
103
, each wafer W is turned circumferentially until the OF edge portion
200
of the wafer faces a certain predetermined direction, and thus orientated wafer W is sucked by a suction cup
104
a
of a setter arm
104
, which swings to bring the wafer to a wafer suction cup assembly
105
, where the wafer is released by the setter arm
104
and sucked and held by the wafer suction cup assembly
105
.
As the wafer suction cup assembly
105
turns, the wafer W adsorbed to the cup due to the negative pressure created thereat (hereinafter “vacuum-held”) is also turned circumferentially and its periphery with chamfers is entirely polished by a turning buff
106
, which is pressed against the periphery of the wafer. The thus polished wafer W is then vacuum-held by a suction cup
107
a
of a remover arm
107
, and transported to a location above a cleaning tank
108
, and there it is released from the remover arm
107
to fall into the cleaning tank
108
to be cleaned with the cleaning liquid contained therein; thus the polishing of the chamfers of the wafer W is completed.
Problems the Invention Seeks to Solve
However, in such conventional wafer chamfer polishing apparatus as described above, each wafer W is passed from the setter arm
104
to the wafer suction cup
105
, and then to the remover arm
107
, and this wafer passing is conducted in the presence of polishing slurry so that not infrequently troubles take place as the wafers W are passed on; such troubles include pollution and physical damages such as chipping of the wafer. What is more, since the cycle time is extended by the length of time required for this wafer passing, the operation efficiency of the polishing apparatus is limited. Thus, in the technology of wafer chamfer polishing, it is desirous that once a wafer is sucked and held by a suction cup the wafer stays on the same cup during the entire process of wafer chamfer polishing.
The chamfers of a wafer W are polished in a manner as shown in FIG.
9
: that is, the buff
106
is pressed on the wafer W laterally such that a buff groove
106
a
formed horizontally in the side wall of the buff
106
is fitted over the periphery of the wafer W. However, in this manner, of the chamfers of the wafer W shown in
FIG. 10
, either the tapered chamfers X
1
and X
2
are first polished and consequently the outermost chamfer X
3
is polished with some delay or vice versa. This results in longer polishing time.
The present invention was made in view of these problems, and it is, therefore, an object of the invention to provide a method and an apparatus for polishing the peripheral chamfers of a wafer which enable elimination of wafer transfer operation and thus improve operation efficiency and dependability.
SUMMARY OF THE INVENTION
Means to Solve the Problems
In order to attain the objects of the invention, there is provided a method for polishing chamfers made along the periphery of a semiconductor wafer comprising steps of picking up a wafer from a wafer supply station, bringing the wafer to a wafer polish station where the wafer's chamfers are polished, bringing the wafer to a wafer clean station where the wafer is cleaned, and bringing the wafer to a wafer discharge station where the wafer is discharged, and this method is characterized in that when the wafer is once picked up by a transportation means at the wafer supply station, the wafer is not released by the transportation means until the wafer is discharged at the wafer discharge station.
This method is applicable to wafers which have an OF periphery, and in this case, both the chamfers along the orientation flat portion of the wafer edge or periphery, hereinafter referred to as an OF periphery and those along remainder of the periphery of the wafer, hereinafter referred to as the non-OF periphery, are polished at the wafer polish station.
The invention also provides an apparatus for polishing the chamfers made along the periphery of a semiconductor wafer, which comprises a wafer supply station from which the wafer is picked up, a wafer polish station where the wafer's chamfers are polished, a wafer clean station where the wafer is cleaned, a wafer discharge station where the wafer is discharged, and a wafer transportation means for picking up the wafer, turning the wafer circumferentially, and transporting the wafer to the wafer polish station, to the wafer clean station, and to the wafer discharge station in this order, and this wafer transportation means is further adapted to keep holding the wafer as it carries the wafer from the wafer supply station until it releases the wafer at the wafer discharge station.
It is also proposed to design the apparatus such that the wafer polish station is capable of polishing both the chamfers along the OF periphery and those along the non-OF periphery of the wafer.
In a first embodiment, the wafer supply station, the wafer polish station, the wafer clean station, and the wafer discharge station are arranged in a row along a straight line, and the wafer transportation means is adapted to transport the wafer in a manner such that the center of the wafer traces a locus identical to the straight line; the wafer polish station including a cup-like cylindrical hollow buff having polishing surfaces both inside and outside the wall of the buff and adapted to rotate axially.
Preferably in this first embodiment the wafer transportation means consists of two wafer holder assemblies each including an arm having a wafer suction cup at the fore end and adapted to shift vertically.
In a second embodiment, the wafer transportation means consists of a circular turn table having rotary wafer suction cups arranged equiangularly along the circumference of the turn table and the turn table is adapted to turn step-wise, each step consisting of a turn through a predetermined angle, and to transport the wafer in a manner such that the center of the wafer traces a circular locus along which the stations are arranged equiangularly.
In a preferred version of the second embodiment, the non-OF chamfers polish substation includes two cylindrical rotary buffs, one of which is formed with a groove in its side wall to receive the non-OF peripheral edge of the wafer in it, the two buffs being arranged in a manner such that they are simultaneously pressed on the periphery of the wafer, which is vacuum-held and turned by one of the rotary suction cups.
In a preferable third embodiment, there is provided a wafer cassette transportation system which is adapted to transport wafer cassettes from the wafer supply station to the wafer discharge station so that a wafer cassette from which wafers have been all taken out at the wafer supply station can serve to receive the polished wafers discharged at the wafer discharge station.
Effects of the Invention
According to the first embodiment of the invention, once a wafer is picked up and vacuum-held by the suction cup of one of the two wafer holder assemblies the wafer W stays on the same cup throughout the series of polishing operation from wafer pick-up till wafer rele

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