Experimental verification of achieving vertical sidewalls for nanoscale features in electron-beam lithography

It is often necessary to achieve a vertical sidewall in the remaining resist profile obtained through electron-beam lithographic process. For nanoscale features, the spatial dose distribution of V-shape typically used in a conventional two-dimensional proximity effect correction scheme cannot easily achieve a vertical sidewall while also minimizing the critical dimension (CD) error. In an earlier study, it was shown through simulation based on a three-dimensional model that new types of spatial dose distributions, i.e., M- and A-shapes, are effective in achieving vertical sidewalls and minimizing the CD error and total dose. These two dose distributions exploit the fact that the exposure varies along the depth dimension with high and low contrasts at the top and bottom layers of resist, respectively. In this study, a number of experiments have been carried out in order to verify the simulation results reported earlier. This paper includes a review of the new dose distribution types and experimental results with a detailed discussion.