Photoresist Characteristics of Polyurea Films Prepared by Vapor Deposition Polymerization

Aromatic polyurea was prepared by vapor deposition polymerization of 4,4′-diaminodiphenyl methane and 4,4′-diphenylmethane diisocyanate, and the mass spectra of the gases obtained from the polyurea by heating were measured. Mass spectrum analysis revealed depolymerization, which is a distinctive feature of polyurea. The polyurea finally evaporated completely at 300°C or lower in a vacuum. A Fourier transform infrared (FT-IR) analysis indicated that polymerization and cross-linking took place between unreacted end groups or urea bonds in the polyurea that was exposed to ultraviolet light. As a consequence, the exposed polyurea did not evaporated even at temperatures greater than 300°C. Exploiting the difference in thermal resistance between the exposed and unexposed polyurea, films were developed by heating, yielding a resolution of 5-micron lines and spaces. It was found that the polyurea can be used as a negative resist material, and that an all-dry lithographic process could be accomplished. In addition, the dielectric strength of the exposed polyurea is 2.5 times as much as that of unexposed polyurea.