Electron beam lithography in thick negative tone chemically amplified resist: Controlling sidewall profile in deep trenches and channels

Abstract

Exposure characteristics of 30keV electron beam lithography in 6μm thick chemically amplified resist SU-8 is reported. The exposure dose variation shows remarkable impact on resolution and sidewall profiles of 3D structures of SU-8. Sidewall profiles of the experimentally realized vertical structures have been analyzed by comparing them with three dimensional electron energy deposition profiles in the resist. The analysis shows that the broadening of the developed structures in excess of a particular energy deposition density contour follows non-monotonic variation. The sidewall profiles indicate that the crosslinking of the resist proceeds in a reaction–diffusion environment in which the photoacid diffusion itself is controlled by crosslink density. We also demonstrate large area fabrication of two types of SU-8 deep channels connected by bridges, by exploiting the energy dependent range of e-beam in the resist.