Vacuum lithography using plasma polymerization and plasma development

Abstract

A completely dry lithography has been proposed which involves plasma polymerization of methyl methacrylate (MMA) and plasma development with CCl 4. It was called vacuum lithography because all processes were performed in a vacuum. However, the developed pattern had a lower resolution than patterns produced by conventional lithography with a wet process. After several technical refinements, the quality of the resist and the developed pattern was markedly improved. In this paper, recent results will be reported. A gas-flow-type reactor was used instead of a bell-jar-type reactor because the morphology of plasma-polymerized MMA (PPMMA) varied with each experimental run which was performed with the same gas and discharge parameters. The monomer vapour was introduced downstream of the argon discharge, and the polymerized film was formed on the substrate placed further downstream in the mixed gas. The development of pattern was performed by etching with an Ar-O 2 mixture and with hydrogen gas instead of CCl 4 gas, because the etching rate of the resist was too high in a CCl 4 plasma and a clear pattern was not obtained. The evaluated sensitivity and γ value of PPMMA were 1000 μC cm −2 and 1 respectively. MMA containing 5% tetramethyltin was also used as a monomer gas for plasma polymerization downstream of the argon discharge. In this case the sensitivity and γ value were 10 μC cm −2 and 2 respectively.