SAFE SOLVENT RESIST PROCESS FOR SUB-QUARTER MICRON T-GATES

With the advent of the ''green'' revolution, the semiconductor industr y must develop alternative processes that utilize environmentally frie ndly products. As a first step toward this end we have demonstrated an electron beam patterned sub-quarter micron T-gate process using safe resists manufactured by Microlithography Chemical Corp. (MCC). Instead of the more conventional chlorobenzene based poly methyl methacrylate (PMMA) and 2-ethoxyethanol copolymer solutions, new anisole based PMM A and an ethyl lactate based copolymer are used. In addition to replac ing the non-environmentally friendly resists, we sought to increase ga te yield by improving the shape of the resist profile. Focused ion bea m (FIB) cross-sectional analysis of 0.2 mu m T-gates fabricated using our conventional process showed metal discontinuity at the stem-to-cap transition. This was attributed to a sharp transition in the resist f rom the bottom layer of PMMA to the copolymer. With the safe resists w e sought to grade the transition between the stem and cap to improve m etal continuity. Multiple techniques were used to evaluate and charact erize the safe resist process. FIB cross sectioning provided a rapid a nd less destructive method for resist profile inspection. In addition, metal deposition was examined prior to liftoff to view evaporation bu ildup. Scanning electron microscopy and atomic force microscopy were u sed to give comparative measures of gate length. A safe resist process for sub-quarter micron T-gate fabrication is described.