Material and Process Development for KrF Lithography using Tri-level Resist Process.

Abstract

A material and process development for tri-level resist process is carried out in terms of both lithography and RIE processes. The goal is to introduce the tri-level resist process into 0.13μm DRAM fabrication. The film stack of the tri-level resist process consists of thermally cross-linked novolak resin (I-line photo resist) as a bottom layer (500-900nm thickness), spin-on-glass (SOG) as a middle layer (70-90nm thickness) and an environmentally stable chemical amplified positive (ESCAP) type KrF photo resist as a top layer (200-300nm thickness). The lithographic process window for 130nm L/S structure using the KrF photo resist is determined to be 0.6um depth of focus (DOF) and 16% exposure latitude, under the exposure condition of 0.68NA, 0.75 sigma and 2/3 annular illumination. The resist pattern of the top layer is transferred to the middle layer and the bottom layer using conventional RIE techniques.A WSi gate structure (nested and isolated lines) capped with SiN film in 0.13um DRAM is formed using the tri-level resist processing.