Undercut elimination in DUV negative systems: application to lithography and etching of metal levels

Abstract

When a negative tone DUV chemically amplified resist is used on TiN, an undercut at the resist/TiN interface can be observed. This effect leads to a limitation of the performance and optimal use of these resists. In our study of the Shipley SNR 200 resist, a typical representative of these formulations, this undercut has been quantified versus soft bake (SB) and post exposure bake (PEB) temperatures, and for different types and times of development. The results obtained show that for high SB temperatures (greater than 120 degrees Celsius), undercut is minimized, whereas for SB lower than 120 degrees Celsius, undercut occurs. Whatever the SB conditions, undercut significantly increases for PEB temperatures above 120 degrees Celsius. The influence of the development parameters is negligible. By using both DSC thermal analysis and the wafer curvature measurement (WCM) technique, the glass transition of the SNR 200 resist has been determined at 115 degrees Celsius. This result clearly correlates the diffusion mechanisms involved in the undercut phenomenon with the viscoelastic properties of the resist. For these optimized lithographic conditions as well as for the metal etch conditions, a 100% electrical yield for isolation patterns was obtained down to 0.35 micrometer spaces.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.