Etch Characteristics of Low-K Materials Using CF3I/C4F8/Ar/O2 Inductively Coupled Plasmas

Abstract

In this study, pulsed CF3I/C4F8/Ar/O2 inductively coupled plasmas have been studied for low-k etching, and the effects of CF3I addition to C4F8/Ar/O2 on the plasma characteristics and etch characteristics of low-k materials were investigated. The increased ratio of CF3I/(CF3I+C4F8) in the gas mixture increased CF3 radicals while decreasing CF2 radicals in the plasma, and which are related to the etching and polymerization, respectively. Therefore, the etch rates of SiCOH increased with increasing the CF3I ratio. However, the etch selectivity over an amorphous carbon layer and photoresist was the highest at the ratio of 0.5 because the CF2/F flux ratio from the plasma and the C/F ratio on the polymer layer were the highest at the CF3I ratio of 0.5. The SiCOH damage was decreased with increasing CF3I ratio and the SiCOH damage appeared to be very low, particularly when the CF3I ratio was ≥0.5 by showing low Si–CH3 bond loss, low F penetration, and a low surface roughness. Therefore, it is believed that, as opposed to the C4F8/Ar/O2 gas mixture only, mixing 50% CF3I into the C4F8/Ar/O2 gas mixtures resulted in not only a high etch selectivity over mask materials, but also a potentially reduced etch damage.