Lithographic technologies for future ULSI

Abstract

The resolution limitations in optical lithography will make the selection of the future lithographic technology the key issue for the future ULSIs. This paper describes several new approaches for overcoming this resolution limit in optical lithography and the potentials for introducing new lithographic technologies such as electron beam and X-ray lithography. The new approaches include the phase shifting technique and modified illumination. The principles and limitations of these new approaches are reviewed. New lithographic technologies are also of keen interest to the semiconductor industry and they may overtake optical lithography. The biggest problem in electron beam lithography is its low throughput. The concept of a cell projection system, which has been proposed to overcome this problem, is discussed. In X-ray lithography, precise mask fabrication is the most important issue for proximity printing. The limitations in 1:1 proximity printing are reviewed and the potentials of a reduction projection system, which is a break-through that eliminates the need to use a 1:1 precise mask, is also discussed.