Process development for 180-nm structures using interferometric lithography and I-line photoresist

A bilayer positive I-line process, based upon the use of a bottom antireflective coating and implementable on a standard processing track, is described for the production of sub-0.2-mu m features by interferometric lithography. Pattern collapse for small, high-aspect ratio photoresist features was found to be a significant issue. The impact of a number of processing variables on pattern collapse was investigated. These variables included resist thickness, substrate reflectivity, developer concentration, post exposure bake (FEB) time and temperature, L/S pitch differences, and development and drying methods. Using a 0.8-mu m resist thickness, a feature width of 180 nm (360-nm pitch) was attainable without a FEB, while with a suitable FEB, 150-nm features could be obtained. A reduction of resist thickness to 0.6-mu m enables 120-nm features to be obtained without a FEB, and 100-nm features with a FEB.