BENCHMARK COMPARISON OF I-LINE, ALTERNATING PHASE-SHIFT MASKS

Phase shift has been seen by many as a route to increase the resolutio n capability of optical microlithography beyond the Rayleigh criterion . The initial enthusiasm with which this technology was greeted has be en moderated by the realization that prior to its practical applicatio n many technical challenges must be overcome. Nevertheless progress ha s been made. The question to be answered is no longer whether phase sh ift works, but rather which phase-shift approach and manufacturing tec hnique provide the best practical solutions. We compare three techniqu es to build alternating phase-shift reticles: (1) deposited spin-on gl ass (SOG), (2) chemical vapor deposition (CVD) silicon dioxide, and (3 ) etched quartz. the merits of each approach are judged in terms of li thographic performance, ease of manufacture, and reliability. We concl ude that the SOG approach offers the best short-term solution to the m anufacture of alternating phase-shift masks, although its lithographic performance is somewhat inferior to the other two and its long-term r eliability remains to be determined. For deposited oxide to be a viabl e long-term approach, the oxide must be deposited under the chrome; fo r etched quartz, the roughness and defect density must be controlled.