A comparative study between organic and inorganic resists in electron beam lithography using Monte Carlo simulations

Abstract

A Monte Carlo study has been performed in order to understand the differences in exposure behavior between organic and inorganic electron beam resists. Typically inorganic resists constitute high atomic number species (Z>10) and are of higher density as compared to traditional organic resists such as acrylates. In this work, the consequences of tethering a high atomic number species such as a silicon or titanium atom onto a PMMA molecule on the electron beam energy deposition in the material have been investigated. The addition of these atoms increases the density of the hypothetical film and therefore the number of elastic and inelastic collisions suffered by an incident electron. The larger electron shell density associated with these high atomic number species more effectively shields the nucleus resulting in a larger average elastic scattering angle but the average inelastic scattering angle remains unaffected. The average radial and depth distance traveled by an incident electron decreases with increasing atomic number of the species tethered to the PMMA molecule. The radial and energy distribution of incident electrons in PMMA, HSQ, and a Titanium based metal-organic precursor film have also been compared. At low accelerating potentials, the broadening of the point source electron beam becomes larger with the increasing atomic number of the atoms in the resist material. However, at high accelerating potentials where the average depth distance traveled into the film increases, the point source electron beam broadening is essentially the same for both organic and inorganic films for thin films. Eventually, at large film thicknesses, the radial spread of incident electrons becomes broader in the inorganic films as a consequence of higher density and larger scattering atoms. Also, as a consequence of a larger number of collisions, the absorbed energy density in inorganic films increases, indicating that these materials will more efficiently capture electron beam energy as compared to traditional organic materials.