A surface-silylated single-layer resist using chemical amplification for deep ultraviolet lithography: II. Limited permeation of Si compounds from liquid phase

A single thick layer of poly(vinyl phenol) containing onium salt was surface-silylated uniformly through contact with hexamethyl-cyclotrisilazane or hexamethyl-disilazane in solution to obtain a bilevel structure, similarly to a previous silylation study in the vapor phase. Silicon atoms were effectively incorporated into the surface sublayer by limited permeation of the solute and reaction with -OH to form -O-SiR₃. The O₂ reactive ion etching (RIE) durability of the silylated sublayer of 170-220 nm thickness was 15-38 times as high as that of the unsilylated bulk layer. The resist layer was patterned by 5-10 mJ/cm² deep ultraviolet exposure, chemically amplified desilylation during postexposure baking, and wet development with alkali to remove the surface sublayer in the exposed area, forming a shallow, recessed image. When the layer, particularly that silylated with hexamethyl-disilazane, was plasma-developed by O₂ RIE, the bulk layer in the exposed area was clearly blanked to the substrate to give a positive-tone image with a high aspect ratio.