Sub-halfmicron negative resist systems by image reversal

Abstract

There has been a rising interest in image reversal of positive working resists. For optical and X-Ray applications, one practical advantage of image reversal is the elimination of the need of two sets of complementary masks to do positive and negative imaging. For direct write serial lithography such as electron beam and ion beam lithography, there is a great saving on writing time if the unexposed areas are much larger than the exposed areas. In this paper, we report the conversion of an e-beam generated positive pattern to a negative pattern by an image reversal technique which employs the filling of the positive trenches with silicon containing materials. The surface of the planarized positive images is etched back in CF4, RIE to reveal the resist surface. A subsequent O2 RIE image transfer step completes the reversal process. The vertical sidewall angles of the positive images have a strong influence over the resulting linewidths of the reversed images. Negative images of excellent linewidth control are obtained using this technique unlike most negative resists which swell during development. This technique allows one to achieve a negative resist pattern which keeps the resolution and the linewidth control of the original positive resist system. The effects of the sidewall slopes of the positive images on linewidth variation of the resulting negative images are discussed. The choice of the planarizing materials to provide good planarization over various sizes of topography and the RIE etchback uniformity will also be described. © 1987, SPIE.