Highly accurate stitching method between cell projection and variably shaped e-beam shots

Abstract

For development and practical fabrication of advanced ultra- large-scale integrated circuits (ULSIs), cell projection (CP) electron beam (EB) lithography has the advantage of high writing throughput, compared with conventional variably shaped (VS) EB lithography. However, when the CP method is used for fabricating advanced ULSIs, the shot stitching accuracy for the minimum feature size between CP and VS EB shots becomes a serious problem. To obtain highly reliable shot stitching accuracy between CP and VS EB shots, we developed a highly accurate stitching method using a cross- correlation method for measurement of the CP EB shot center position. By using the cross-correlation method between ideal and practical detected signals, an estimation stability error of less than 10 nm for the position of the CP EB shot center was achieved. We applied this proposed method in Gbit DRAM pattern fabrication. The mean value for the EB shot stitching accuracy was always suppressed to less than 10 nm. As a result, we obtained a shot stitching accuracy of less than 25 nm between CP and VS EB shots.