Full three-dimensional characterization of 25nm lines for chemically amplified resist simulation

Abstract

Low molecular weight negative tone chemically amplified resist has been exposed with 100kV electron beam writer with a postexposure bake temperature varying between 85 and 100°C. Isolated lines, with feature size ranging from 20 up to 100nm, have been characterized with scanning electron microscopy and critical dimension atomic force microscopy. A simple kinetic reaction law and lateral acid diffusion into the resist layer were taken into account for the cross-linking reaction simulation. Top view and full three-dimensional measurements of resist feature have been fitted with an analytical expression. A cost function was introduced to extract the reaction order (m) and the acid diffusion coefficient (D) of the second Fick’s law. Whatever the process temperature used, a constant value for m(m=2.6) was found, and D was found to vary from 2to45nm2∕s for a postexposure bake temperature of 85 and 100°C, respectively. Depending on the metrology technology used for resist characterization resist parameter extraction may be significantly impacted, especially for very narrow resist line simulation.