SILYLATED ACID HARDENED RESIST PROCESS - A DEEP ULTRAVIOLET SURFACE IMAGING TECHNIQUE

A deep ultraviolet surface imaging technique using a silylated acid hardened resist (SAHR) is described. The resist, Shipley XP-8928, contains a meta, para-cresol novolak resin which has a high optical absorbance in the deep ultraviolet (DUV). This reduces complications from substrate reflections and restricts the image to the near-surface regions. The exposed regions, which become crosslinked, are less susceptible to vapor silylation by agents such as trimethylsilyldiethylamine (TMSDEA). The unexposed regions may be easily silylated. An anisotropic oxygen reactive ion etching is used to transfer the surface image through the bulk of the resist. This paper discusses the kinetics of silylation with TMSDEA, the resulting silicon distributions in the film before and after etch, and the lithographic performance of the process. Silicon distribution throughout the film is determined by Rutherford backscattering spectrometry and illustrated by stained cross sections. It is found that the film surface saturates at a Si content of 9-10 wt. %, and further silylation results in a sharp front at this concentration moving deeper into the film. The rate at which the front moves is determined by the temperature, pressure and the degree of crosslinking. The etch barrier formed at the surface of the resist has been investigated by x-ray photoelectron spectroscopy. This indicates that the surface oxidation of both carbon and silicon is increased, while the silicon concentration is unchanged from unetched samples. This process is capable of producing 0.5-mu-m line/space pairs when exposed by a 0.35 numerical aperture (NA) lens at 248 nm with as little as 7 mJ/cm2. These features can be produced with flat tops and steep sidewalls. Isolated lines with very high aspect ratios can be produced.