Monte Carlo simulation of substrate photoelectrons in hard X-ray lithography and the effect of buffer layer

Abstract

Hard X-ray lithography was introduced for 50 nm generation and beyond due to its shorter wavelength and higher resolution than the soft X-ray (Khan et al, 1999). Photoelectron blur increases in hard X-ray lithography because more photo and Auger electrons are generated at the resist-substrate interface and the resist photoabsorption decreases as photon energy increases from soft X-ray to hard X-ray. This blur, due to secondary electrons at the line edge, is considered to cause pattern degradation. In this paper, Monte Carlo simulation of photo and Auger electrons for this harder spectrum of 2.36 keV average energy was carried out based on Murata's model (Murata et al, IEEE Trans. Electron Dev. vol. ED-32, p. 1694, 1985) and the work of Seo et al (J. Vac. Sci. Technol. B vol. 18, no. 6, p. 3349, 2000). Energy loss density and electron trajectories for 200,000 photons were calculated and plotted in a 200 nm thick TDUR-N908 resist on a W and Si substrate without a buffer layer and with buffer layers of various thickness (Si/sub 3/N/sub 4/ and SiO/sub 2/) on a W substrate between resist and substrate. The buffer layers are 10 nm buffer (10 nm Si/sub 3/N/sub 4/), 30 nm buffer (10 nm Si/sub 3/N/sub 4/+20 nm SiO/sub 2/) and 70nm buffer (10 nm Si/sub 3/N/sub 4/+60 nm SiO/sub 2/).