We report on an investigation of a so-called image-reversal process where a negative tone image can be obtained with a positive resist. The reversal process is achieved by addition of a base to the exposed photoresist and a subsequent flood exposure. First, we characterize the image reversal by means of the characteristic curves, thus optimizing the process. A simple analytical model and a two-dimensional numerical simulation program have been developed in order to evaluate the dependence of the edge slope of the image-reversed resist line on resist and exposure parameters. Experimental investigation confirmed the simulation result that both positive and negative line edge slopes can be achieved with the image-reversal process by properly adjusting the exposure parameters. Finally, the image-reversal process has been compared experimentally to the standard positive process, considering linewidth control on profiled surfaces.
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Klose et al. (1985) studied this question.