Issues and challenges of double patterning lithography in DRAM

Abstract

Double patterning lithography has been one of the candidates for sub-40nm patterning era, and has a lot of process issues to be confirmed. Last year, we presented the issues in double patterning lithography with a real flash gate pattern. Process flow was suggested and CD uniformity due to overlay was analyzed. And the layout decomposition and the two types of double patterning of positive and negative tone were studied with 1-dimensional pattern. In this paper, the implementation to DRAM patterns is examined, which consist of 2-dimensional patterns. Double patterning methods and the selection of their tone for each layer are studied, and the difficulties from the randomness of core pattern are also considered. As a result, DRAM patterns have more restrictions on the double patterning method and selection of tone, and the aggressive layout decomposition should be designed to solve the difficulty in core patterning. Therefore, 37nm DRAM layout can be patterned and the overlay control and cost still remain as dominant obstacles.