A Single Expose Double Develop (SEDD) process for self-aligned lithographic applications

Abstract

A Single Expose Double Develop process has been developed which incorporates the use of a tridensity mask to expose two self-aligned patterns in conventional photoresist with one masking step. This minimizes masking cycles and overlay errors which translates into increased yield. The resultant pattern can be customized for various applications, e.g. obtaining two dopant profiles with a single implant using a dual thickness photoresist pattern, transferring two patterns into underlying films with no alignment error using RIE or wet etching, etc... Experiments are shown which optimize the processing parameters of the photoresist to the density levels in the mask, utilizing characteristic curves for analysis. Process control is correlated to these curves through modelling and experiment. Examples of the applications of the SEDD process in VLSI devices and packaging are shown with SEM photographs. © 1989.