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

• Exposure characteristics of 30 keV e-beam lithography in thick SU-8 is reported.
• Evolution of sidewall profile of 3D structures with exposure dose is analyzed.
• Sidewall profiles of the structures are compared with electron energy deposition profiles.
• Sidewall profile variation indicates cross-linking in SU-8 proceeds via reaction–diffusion.
• Novel bilayer micro/nano-structure fabrication with e-beam is demonstrated.

Exposure characteristics of 30 keV electron beam lithography in 6 μm 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.

The sidewall profiles of the SU-8 pillars (left) and the corresponding electron energy deposition density profiles (right) in the SU-8 resist.Figure optionsDownload as PowerPoint slide