“Safe” solvent resist process for sub-quarter micron T-gates

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With the advent of the “green” revolution, the semiconductor industry must develop alternative processes that utilize environmentally friendly 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 PMMA and an ethyl lactate based copolymer are used. In addition to replacing the non-environmentally friendly resists, we sought to increase gate yield by improving the shape of the resist profile. Focused ion beam (FIB) cross-sectional analysis of 0.2 μm 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 from the bottom layer of PMMA to the copolymer. With the safe resists we sought to grade the transition between the stem and cap to improve metal continuity. Multiple techniques were used to evaluate and characterize the safe resist process. FIB cross sectioning provided a rapid and less destructive method for resist profile inspection. In addition, metal deposition was examined prior to liftoff to view evaporation buildup. Scanning electron microscopy and atomic force microscopy were used to give comparative measures of gate length. A safe resist process for sub-quarter micron T-gate fabrication is described.