Investigation of electron beam stabilization of 193-nm photoresists

Abstract

193nm lithography is a promising candidate for the fabrication of microelectronic devices at the l3Onm design rule and below. With smaller feature sizes, below l3Onm, reduced resist thickness is essential because of the pattern collapse issues at high aspect ratios and the limited depth of focus with 193nm lithography tools. However, ArF resists have shown problems with etch selectivity, especially with the thin resist layers necessary. Additionally, pattern slimming during CD-SEM measurement, due to the nature of the resist chemistry, is an issue with feature stability after patterning.At present, many studies have been performed for improving the etch selectivity of resists and addressing line slimming issues. In this study, the electron beam stabilization process has been applied for improving the etch selectivity of resist patterns having an aspect ratio less than 3.0. The electron beam stabilization has been applied to two different ArF resist types; acrylate and cyclic-olefin-maleicanhydride (COMA), which have been evaluated with respect to materials properties, etch selectivity, and line slimming performance as a function of electron beam dose and etch condition.Film shrinkage and the change in index of refraction were monitored as a function of stabilization condition. The chemical properties were characterized before and after electron beam stabilization using FTIR analysis. Blanket resist etch rate studies were performed as a function of stabilization condition for each resist type. Cross-sectional views of resist patterns after etch processing were also investigated to evaluate the improvement in etch resistance provided by the electron beam process. CD SEM measurements were performed to evaluate the impact of the stabilization process on the patterned features. The issue of line slimming has also been evaluated, with and without electron beam stabilization, for the different ArF resist materials considered. The results were compared with a KrF resist currently used in production. Based on the experimental results, the electron beam process provides a method for improving etch selectivity and reducing line slimming issues of ArF resists.

Etch Properties of 193nm Resists: Issues and Approaches.

“…6). Kim et al 4 have reported that resists based on poly(norbornene derivative/malefic anhydride) or "COMA" type shrink more (30 %) compared to methacrylate (18 %) using the same standard ebeam curing process as the current study. Although a direct comparison is not possible as the acid sensitive groups are different, it is reasonable to assume that the hybrid type would have shrinkage between that of COMA and pure methacrylate.…”

“…It has been reported that 193nm resists of the kinds shown in Scheme 1 undergo a loss of carbonyl groups upon a-beam curing and moderate changes in the C-H, C-H2 and C-H3 bonds in the 3000-2800 cm l region [3][4]. In this study, the influence of three different processes, viz., standard, LT and ESC, on the level of carbonyl loss in the FTIR were observed.…”

“…F t 3.3 Effect of a-beam curing on the etch rate and surface roughness after etch E-beam curing process has been reported to improve the etch rates of 248 and 193nm resists [1][2][3][4]. Three different processes of e--beam curing namely standard (uncontrolled wafer temperature), LT (low temperature) and ESC (medium temperature) were studied to understand the influence of the curing processes on the etch rate, surface roughness and pattern profiles.…”

“…The second decay process has been assigned to the evaporation of residual solvents.l It is to be expected that during the a-beam curing process the residual solvent and other volatiles are mostly eliminated, a drastic decrease leading to almost no change in the CD during CD SEM measurements. 4 curing. The LT process shows the least shrink compared to the ESC and standard processes.…”

“…As modification of polymer backbone often results in big differences in the lithographic performance, only minor modifications are being carried out. On the process side, a-beam curing of 193nm resists is found to offer improvement in etch as well as elimination of surface roughness issues [1][2][3][4]. In this paper we report the etch characteristics of several 193nm polymers/resists as well as the benefits of a-beam curing on the etch characteristics, CD SEM stability.…”