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IP.com Disclosure Number: IPCOM000004776D
Original Publication Date: 2001-May-16
Included in the Prior Art Database: 2001-May-16
Document File: 6 page(s) / 39K

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Karl E. Mautz: AUTHOR [+1]



This text was extracted from a WORD97 document.
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by Karl E. Mautz and Clint Haris

End effectors are a hardware apparatus used to contact and support silicon wafers from underneath and are connected to robotics to move wafers from one location to another. An example of this movement is the transfer of a wafer (or wafers with a multi-fingered End effector) from a wafer holder system including: 1) a cassette, 2) SMIF (standard mechanical interface mini-environment wafer holder for 200mm and smaller wafers), or 3) FOUP (front opening unified pod used for 300mm silicon wafers) to a process tool or chamber.

An improvement in End effectors can be realized if they have the ability to sense their location relative to: 1) a wafer holder, 2) the wafer to be transferred (picked), and 3) the wafers immediately above and below the picked wafer. The End effector's successful transfer of the wafer is dependant on maintaining clearance from all objects that could scratch, damage, or cause particulates and other defectivity on the picked wafer. Wafers held in holders are separated by a standardized distance called a pitch. The trend in the industry is to reduce the pitch to allow greater packing efficiency of the wafers. This requires increased accuracy and precision in the motion of the End effector. These motions are: 1) position and insert itself between the wafer to be picked and the lower wafer, 2) lift up the picked wafer off of the holder rails, 3) extract itself from the holder, and 4) transfer the wafer to the desired delivery point.

Of these motions, the most problematic is the insertion motion. This is due to the positioning of the wafers in the holder. The wafer's spatial position is effected by gravity (wafer bows in the center downward from the support rails), stress (wafers can be warped due to the influence of high temperature processes and blanket film forces on the wafer backside), particles and defectivity on the wafer backside or rails that can cock the wafer from the horizontal plane, incorrect loading of wafers from a transfer apparatus that cross-slots (tilts) the wafers in non-horizontal rail placement, and holder or rail guide warpage that causes deviations from the horizontal plane. These position influences are accumulative and cause errors in the insertion, wafer pick and extraction motions.

End effectors are programmed by setting distances relative to a fixed point of reference (usually the bottom of the holder or lower-most wafer position). From this point all insertion, pick, and extraction motions are based on distance calculations unless special teaching procedures are used to optimize the motions for deviations in the holder design or linearity of the End effector robot motion.

The 300mm standard pitch (separation) of wafers in a FOUP or other staging cassette is 10mm. This is to allow for the bowing or warping of 300mm wafers (in the cen...