CHF3 Dual-Frequency Capacitively Coupled Plasma by Optical Emission Spectroscopy

We investigate the intermediate gas phase in the CHF3 13.56 MHz/2 MHz dual-frequency capacitively couple plasma (CCP) for the SiCOH low dielectric constant (low-k) film etching, and the effect of 2 MHz power on radicals concentration. The major dissociation reactions of CHF3 in 13.56MHz CCP are the low dissociation bond energy reactions, which lead to the low F and high CF2 concentrations. The addition of 2 MHz power can raise the probability of high dissociation bond energy reactions and lead to the increase of F concentration while keeping the CF2 concentration almost a constant, which is of advantage to the SiCOH low-k films etching. The radical spatial uniformity is dependent on the power coupling of two sources. The increase of 2 MHz power leads to a poor uniformity, however, the uniformity can be improved by increasing 13.56 MHz power.