Effects of Bias Pulsing on Etching of SiO₂ Pattern in Capacitively-Coupled Plasmas for Nano-Scale Patterning of Multi-Level Hard Masks

In order to study the effects of bias pulsing on the etching characteristics of a silicon dioxide (SiO₂) layer using multi-level hard mask (MLHM) structures of ArF photoresist/bottom anti-reflected coating/SiO₂/amorphous carbon layer (ACL)/SiO₂, the effects of bias pulsing conditions on the etch characteristics of a SiO₂ layer with an ACL mask pattern in C₄F₈/CH₂F₂/O₂/Ar etch chemistries were investigated in a dual-frequency capacitively-coupled plasma (CCP) etcher. The effects of the pulse frequency, duty ratio, and pulse-bias power in the 2 MHz low-frequency (LF) power source were investigated in plasmas generated by a 27.12 MHz high-frequency (HF) power source. The etch rates of ACL and SiO₂ decreased, but the etch selectivity of SiO₂/ACL increased with decreasing duty ratio. When the ACL and SiO₂ layers were etched with increasing pulse frequency, no significant change was observed in the etch rates and etch selectivity. With increasing LF pulsebias power, the etch rate of ACL and SiO₂ slightly increased, but the etch selectivity of SiO₂/ACL decreased. Also, the precise control of the critical dimension (CD) values with decreasing duty ratio can be explained by the protection of sidewall etching of SiO₂ by increased passivation. Pulsebiased etching was successfully applied to the patterning of the nano-scale line and space of SiO₂ using an ACL pattern.