New types of dose distributions for vertical sidewall minimizing total dose in 3-D electron-beam proximity effect correction of nanoscale features

Abstract

The spatial dose distribution across a feature, derived by a conventional 2-D proximity effect correction scheme, is a “V-shape,” i.e., higher dose closer to edges. With such a dose distribution, it is extremely difficult to realize a vertical sidewall in the resist profile for nanoscale features while reducing the critical dimension (CD) error. In this paper, it is shown that, in order to achieve a vertical sidewall of nanoscale feature with the minimum total dose, a dose distribution of a shape other than the V-shape must be used. This is due to the fact that the lateral development of resist becomes comparable to the vertical development for nanoscale features and the exposure varies along the depth dimension with high and low contrasts at the top and bottom layers of resist, respectively. Based on these characteristics, new types of dose distributions, i.e., “M-shape” and “A-shape,” have been derived to achieve a target resist profile of a vertical sidewall while minimizing the total dose. The simulation results show that the new dose distribution types lead to a more vertical sidewall, a smaller CD error, and a lower total dose.