Sensitivity, contrast and development process in electron and ion lithography

Abstract

The dependence of the resist solubility rate S on the average exposure dose D (or on the adsorbed energy per 1 U resist volume) makes it possible to optimise the used sensitivity (or the dose requirements) to achieve the needed contrast at chosen development conditions for an arbitrary combination of resist–developer (i.e. at a given molecular weight, resist density and radiation efficiency of the charged particles). Two cases of this relation S( D) are distinguished. In the first of them a universal dependence S( D) is obtained during the development process with one and the same solubility rate. In the second case the obtained dependence S( D) is a multi-valued function of a non-linear solubility rate during the development process for a different developing time. The contrast parameter value γ s (proportional to the traditionally used contrast parameter γ d) is determined by the slope of the dependence S( D). One and the same resist–developer couple can show high sensitivity at a low contrast value and a high contrast value at lower sensitivity for different conditions. The contrast is a function of the developing time and the dose in the case of a non-linear S( D) dependence. A mathematical model and results for the resist surface evolution in electron and ion beam lithography are also presented.