The use of contrast enhancement layers to improve the effective contrast of positive photoresist

The analytic solution of Babu and Baruch to the dynamic bleaching problem is used to evaluate the merit of contrast enhancement layers in photolithography. A CEL performance criterion is defined as the effective gain in resist system contrast. This gain is evaluated as a function of the CEL and resist parameters. The performance gain is maximized if the product of CEL sensitivity and resist "dose to clear" exceeds one. Universal curves are also given for the evaluation of the CEL transmission function. It is found that nonbleachable absorption in the CEL degrades the performance if its magnitude exceeds a few percent of the bleachable component.