Study on fine patterning processes with a thick resist

Abstract

Abstract The processes to define an approximately 1–2 μm sized fine pattern with a 15 μm thick resist are studied by using near-UV (436 nm) and X-ray (∼ 7 A) lithographies, as well as a multi-layer resist process using the dry etching technique. The X-ray sensitivity curve for a novolac-diazoquinone resist, which is used as the alternative to PMMA, is obtained. The resist has a slightly higher sensitivity, ∼ 1400 mJ/cm2, but much poorer contrast (γ), 1.15, compared to PMMA. The most serious problem in the lithography process is found to occur at the exposure step, where the N2 gas, generated by the photochemical transformation of the quinonediazide sensitizer, causes compressive stress in the resist film, resulting in pattern deformation. Optimization in the overall lithography steps is discussed to compensate for (i) the poor resist contrast and (ii) the gas generation due to the exposure. The wall steepness of the resist pattern is also compared between the X-ray and UV lithographies. This preliminary experiment shows that the X-ray lithography can be used to define a pattern finer than 0.8 μm in a thick resist, while the near-UV lithography is used to define a pattern wider than 3 μm.