Chemistry of Materials

Airborne Contamination of a Chemically Amplified Resist. 1. Identification of Problem

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The lithographic performance of a chemically amplified resist is severely degraded by vapor from organic bases. This effect is very pronounced and can be observed when the coated wafers stand for only a few minutes in air containing parts per billion (ppb) levels of an organic base. In resist systems derived from poly[4-((tert-butyloxycarbonyl)oxy)styrene], the contamination induced effect takes two general forms. When processed in the negative tone, the UV exposure dose required to obtain the correct linewidth increases. When processed in the positive tone, a “skin” forms at the resist-air interface. Both effects are caused by the photogenerated acid being neutralized by the airborne organic base. A wide variety of commonly used materials liberate trace amounts of volatile amines and degrade resist performance. We have quantified the incorporation of one such airborne contaminant, N-methylpyrollidone (NMP), by thin polymer films. NMP labeled with 14C was introduced at a concentration of 10 ppb into a stream of purified air and the films of interest were allowed to stand in the airstream for a predetermined time under controlled conditions. This method allows for determining NMP uptake rate, correlating lithographic performance with absorbed NMP content, and studying the effects of film thickness or composition on absorption rates. © 1993, American Chemical Society. All rights reserved.