Wafer Cooling and Photoresist Masking Problems in Ion Implantation
A review of wafer cooling considerations in ion implantation systems is given, with emphasis on figures of merit for the various schemes. Estimates of maximum wafer temperature are determined for practical cases of interest, where negligible heat transfer, radiation cooling, or conduction cooling takes place. Modeled and measured wafer temperatures are presented for both one wafer at a time X-Y scanning and large batch pre-dep systems. Problems with the use of photoresist masking at high dose levels and high beam powers include degradation of photoresist, outgassing in the implanter, and difficulty in stripping ion implanted photoresist. A simple model for photoresist damage relates some of these effects to the implant parameters (ion, energy and dose) through the width of a carbonized region which is formed as a result of damage to the photoresist.
KeywordsSheet Resistance Carbonize Region Critical Dose Conduction Cool Wafer Temperature
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