Method for correcting proximity effects in electron beam lithography

Abstract

A proximity effect correction method for electron beam lithography suitable for high voltages and/or very dense patterns applies both backscatter and forward scatter dose corrections. Backscatter dose corrections are determined by computing two matrices, a 'Proximity Matrix' P and a 'Fractional Density Matrix' F. The Proximity Matrix P is computed using known algorithms. The elements of the Fractional Density Matrix are the fractional shape coverage in a mesh of square cells which is superimposed on a pattern of interest. Then, a Dose Correction Matrix D is computed by convolving the P and F matrices. The final backscatter dose corrections are assigned to each shape either as area-weighted averages of the D matrix elements for all cells spanned by the shape, or by polynomial or other interpolation of the dose correction field defined by the D matrix. The D matrix also provides a basis for automatic shape fracturing for optimal proximity correction. Optionally, forward scattering correction may be included in the correction process. Forward scattering correction consists of boosting the dose applied to shape i by a factor b.sub.i. These boost factors are computed in a separate and independent step which considers only forward scattering. They are combined with those resulting from the backscatter correction scheme either by simple multiplication to form the final correction factors, or by inputting them to the backscatter correction scheme as numerical weights for each shape.