Patterning of Si₃N₄ layer in pulse-biased capacitively-coupled plasmas for multi-level hard mask structures

The effects of bias pulsing on a Si₃N₄ layer masked with multi-level hard mask (MLHM) structures of KrF photoresist/bottom anti-reflected coating/SiO₂/amorphous carbon layer (ACL) in CH₂F₂/CF₄/O₂/Ar mixture gas chemistry on the etch characteristics of a Si₃N₄ layer were investigated at various bias pulsing conditions in dual-frequency capacitively-coupled plasmas (CCPs). With decreasing duty ratio, the etch rates of Si₃N₄ and ACL decreased. The etch selectivity of Si₃N₄ to ACL under bias pulsing mode was higher than that under continuous wave (CW) mode. Although the Si₃N₄ layer and ACL were etched with increasing pulse frequency, no significant change was observed in the etch rates and etch selectivity. The critical dimension (CD) values with bias pulsing mode were higher with increased sidewall passivation than those under CW mode. Also, the average CD value was the highest and the etch profile was most vertical with the duty ratio of 50% than those with other conditions. In addition, the line-edge roughness (LER) values decreased with the increased duty ratio. The use of bias pulsing in dual-frequency CCPs can finely control the etching process of the Si₃N₄ layer in a MLHM structure.