Proton beam micromachining dose normalization for SU-8 using ionoluminescence detection

Proton beam micromachining (PBM) allows the production of small, intricate, high aspect ratio structures with smooth sidewalls by direct writing MeV protons beams in resist materials such as SU-8 and PMMA. The process depends on the correct incident dose of protons, and conventional normalizing methods using RBS have been utilized previously. However for accelerated (sensitive) resists such as SU-8, the yield of backscattered ions, particularly for small structures, is insufficient for accurate dose measurement. We have used the more prolific ion induced photon emission from SU-8 as a dose normalizing signal for PBM. The SU-8 emits radiation at a wavelength of 560 nm under proton irradiation, and the yield per incident proton depends on the thickness of the resist layer. The photon yield per incident proton has a maximum value at a dose of 25 nC mm-2. The photon normalization method has been used to good effect to micromachine a complex shape with resulting good edge definition