Sub-0.5 µm Lithography Using an Excimer Laser at 248 nm

Abstract

The advent of deep ultra-violet (DUV) lithography using an excimer laser stepper at 248 nm has extended the capability of photolithography in achieving sub-0.5 µm resolution required for the fabrication of 64MB DRAM and 16MB SRAM. This paper reports on the progress of our DUV R&D efforts in working toward this goal. To qualify the stepper, electrical wafer probing was found effective in providing a large volume of data with high sensitivity, accuracy, and precision in the measurements. Advanced resist materials based on the chemical amplification principle demonstrated good sub-0.5 µm resolution, excellent sensitivity, and good etch selectivity required for DUV lithography. However, resist processes for both the positive and negative tone materials still require further optimization incorporating the use of anti-reflective coatings (ARC). Spin-on organic ARC has proven feasible in eliminating both thin-film interference effects and reflective notching. DUV lithography promises to be a strong contender for the next generation of ULSI fabrication, where the limiting factor may lie in the high cost of advanced resist and ARC materials.