Ion Beam Exposure of Resist Materials

Abstract

Ion beam exposure characteristics of a positive resist, poly (methylmetacrylate) (PMMA), and a negative resist, poly(dimethylsiloxane) (PDMS), are studied. It is found that sensitivities to helium and argon ions in terms of electronic charge per unit area are much higher than in the case of electron exposure. Moreover, contrasts, gradients of the exposure characteristic curves, are somewhat better in ion exposure. Using the energy deposition rate of ions calculated from an extended LSS theory, the radiation yields for crosslinking and main chain scission are estimated. The radiation yields caused by collisions of the incident ion with electrons in the polymer are nearly equal to those in electron exposure. On the other hand, the radiation yields caused by nuclear collisions are one‐half in PMMA and one‐fifth in PDMS as large as the radiation yields in electron exposure. In order to investigate applicability of ion exposure to the lithographic process, a simple pattern of 2.7 μm width slit is duplicated. From the cross‐sectional views observed with a scanning electron microscope, it is found that high fidelity and high resolution pattern forming is possible. A fabricating method of proximity contact between a mask and a resist film is proposed.