20 nm contact hole (C/H) patterning is applicable for sub-22 nm technology node applications. Dependence of C/H
CD window on critical process parameters is important for process stability and repeatability. Post applied baking
(PAB) condition, resist thickness, develop time, and dry etch rate are considered to be the most important process
parameters for e-beam chain scission resist ZEP520A C/H patterning. In this paper, PAB temperatures (TPAB) are
investigated at temperatures between lower than glass transition temperature (TG) and much higher than TF. Effects of these process parameters on 20 nm +/-10% C/H CD window for various pattern densities and e-beam doses are
studied. The critical process parameters are determined by their effects on CD window size, C/H sidewall profile,
proximity effect immunity, ΔCD/ΔDose slope, and etch selectivity.
Experimental results are summarized below. Thinnest ZEP520A film has the largest 20nm +/-10% CD window on
D-D plot for various L/S ratios and doses. The dosage window of smaller C/H CD is larger. The proximity effect is
negligible for 50 nm ZEP520A baked at 200°C/300 sec. No apparent effect is found in CD window on D-D plot for develop time as short as 30 sec. PAB condition is most critical than the other process parameters in determining resist density and polymerization which affect e-beam scattering and chain scission in resist film and therefore affects CD resolution and window. PAB condition of 140°C/60 sec is most desirable in terms of CD window on D-D plot, C/H sidewall profile, dry etch rate and proximity effect.