Material or article handling – Apparatus for moving intersupporting articles into – within,... – Stack forming apparatus
Patent
1989-11-21
1992-04-07
Spar, Robert J.
Material or article handling
Apparatus for moving intersupporting articles into, within,...
Stack forming apparatus
414417, 414331, 414757, 414433, B65G 106
Patent
active
051022915
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to methods for transporting silicon wafers, in particular such methods in which the wafer is aligned, and apparatus which is suitable for use in such methods. It includes the methods and apparatus disclosed in, commonly assigned U.S. application Ser. No. 052,496, filed May 21, 1987, now abandoned, as well as further improvements of that method and apparatus.
2. Introduction to the Invention
In the manufacture of solid state devices, silicon wafers are moved between different work stations, often in cassettes which hold a number of spaced-apart wafers stacked next to each other in pockets. Many processes require that the wafer is precisely aligned. The alignment required may be the precise positioning of the center of the wafer and/or the precise orientation of the wafer relative to its crystalline plane, which is indicated on the wafer by a marker of some kind, usually a flat or notch on the perimeter of the wafer. The transporting of individual wafers (including in particular their removal from cassettes, their placement into cassettes, and their alignment, as well as their simple transport from one location to another) is a matter of vital concern to the semiconductor industry.
Known methods of transporting individual silicon wafers involve contact between (a) the underside of the wafer and (b) solid support surfaces or air jets which are likely to contain solid particles. It is already known that these methods can damage or contaminate the underside of the wafer, but this has not hitherto been a matter for concern. However, it has now been found that these known methods can also damage or contaminate the working surface of the wafer.
SUMMARY OF THE INVENTION
This invention provides for the first time, a method and apparatus for transporting an individual silicon wafer in which there is substantially no inherent danger of damaging or contaminating the working surface of the wafer. The term "transporting" is used herein in the broad sense indicated above to include any process in which the wafer undergoes directional and/or rotational movement.
This invention not only provides important advantages in the ease, reliability and speed with which wafers can be transported, in particular when alignment of the wafers is needed. In addition, since the invention substantially reduces or eliminates the possibility of damage to the underside of the wafer, it also opens the way to silicon wafers which have two working surfaces. Thus the method of the invention can be used to transport wafers which have been etched or plated or otherwise modified on both surfaces thereof. For example, connection pads which are now placed on the working surface, where they occupy valuable space, can now be placed on the opposite surface. Such novel silicon wafers form part of the present invention.
In another aspect, this invention provides a method of transporting an individual silicon wafer wherein the wafer is supported solely by means of wafer supports, preferably flanged rotatable wheels, which contact the wafer only around the periphery thereof, thus eliminating the need to contact either of the surfaces of the wafer. A preferred method also includes the step of moving the wafer supports so as to move the wafer, while it is supported and contacted only by the wafer supports, until it has a desired alignment. The movement of the wafer may be lateral only, so as to precisely locate the center of the wafer, or rotational, so as to precisely locate an alignment marker which indicates the crystalline plane of the wafer, or both.
In another aspect, this invention provides apparatus which is suitable for use in the method defined above and which comprises which a wafer to be transported can be supported solely by contact between the periphery of the wafer and the wafer supports and (ii) an open position in which a wafer to be aligned can be passed freely between the wafer supports. rotationally into a desired alignment by movement of the wafer supports, an
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Hine Design Inc.
Katz Robert S.
Richardson T. H. P.
Spar Robert J.
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