Linesize effects on ultraviolet reflectance spectra

Abstract

We have investigated the effect of resist thickness, linewidth, and pitch on UV reflectance spectra. This technique exploits the property that conventional novolak resists are very absorptive from 200 to 300 nm, while substrates are significantly more reflective. For line-space developed resist features of constant pitch, we observe that the reflectance in this wavelength range varies periodically with ? and increases linearly with decreasing linesize. The dominant factor in wavelength dependence is the constructive/destructive interference of the measurement light from the air-resist and air-substrate interfaces. The linesize dependence at constant pitch and resist thickness is predominantly controlled (within proper boundary-condition regimes) by the percentage of the substrate exposed. The gross periodicity of the deep UV (DUV) reflection spectra for patterned films is correlated with resist thickness in a manner similar to the resist-thickness dependence of UV reflection spectra for unpatterned films. Simulation of DUV reflectance from patterned films showed semiquantitative agreement with experimental results.