Polysulfone-novolac resist for electron beam lithography: part I. fundamental studies of resist properties

Abstract

The goal of this work was to develop a resist material for high-keV (&gt;=10 keV) electron beam patterning with: (1) high sensitivity (~10 (mu) C/cm<SUP>2</SUP> 50 keV), (2) high contrast, and (3) etch resistance comparable to current optical resists. In this work, an approach was desired that (1) used multi-component resist design to decouple sensitivity and etch performance and improve contrast but (2) avoided environmental stability problems. Therefore, a resist design first proposed by researchers at IBM in the late 1980s that uses an electron beam sensitive polymeric dissolution inhibitor (poly (2-methyl-1-pentene co 2-ethoxyethyl-methallyl ether sulfone)) in conjunction with novolac resins was explored in this work. In this paper, the fundamental behavior of the polysulfone dissolution inhibitor upon exposure to e-beam and heat was studied. This behavior establishes the processing window for the polysulfone dissolution inhibitor. The thermal stability of polysulfone was studied using TGA, FTIR, and mass spectrometry. The results show that accelerated decomposition of polysulfone occurs above 150 degree(s)C. Polysulfone decomposition upon exposure to e-beam was studied using (1) ellipsometry, (2) quartz crystal microbalance methods, and (3) FTIR. The results of this study show that polysulfone is highly sensitive to electron beam exposure and most of it decomposes at a very low nominal e-beam dose.