Modification of 193nm(ArF) photoresists by electron beam stabilization

For the sub 130nm technology nodes, 193nm(ArF) lithography has become the technology path of choice. Similar to the 248nm technology set, the resist systems being used for 193nm lithography are based on chemical amplification to achieve high throughput at the low exposure energy at 193nm. The current ArF resist systems have experienced problems with etch selectivity and line slimming during CD-SEM measurement. Both of these issues are related to the resist platform and constituents used to achieve the desired lithographic performance. This investigation evaluates electron beam stabilization as a way of addressing both the etch selectivity and line slimming issues associated with some of the current 193nm resist systems. Varying levels of electron beam dose were evaluated in an attempt to understand the effects of energetic electrons on ArF resist materials. Chemical changes in the resist were monitored for blanket resist films by FTIR, film shrinkage, and changes in index of refraction, all as a function of dose level. An increase in modification of the resist is seen with increasing dose. Blanket resist etch rate studies were performed as a function of stabilization condition. The etch rate of the resist was found to decrease with increasing dose as compared to untreated resist. Correlation of the chemical changes and etch rate reductions are proposed for the resists considered. The CD changes induced by the electron beam stabilization were monitored as a function of dose applied. Minimal CD change was seen as a result of the stabilization process. The impact of the electron beam process on line slimming was evaluated by performing repeated measurements on resist features with different levels of electron beam dose. The line slimming was found to be significantly reduced for the higher dose levels considered. Etch selectivity was evaluated by cross-section SEM measurements after etch of features with different levels of stabilization. An increase in the etch selectivity and pattern stability were observed with increasing stabilization dose.