Improvement in etch selectivity of SiO2 to CVD amorphous carbon mask in dual-frequency capacitively coupled C4F8/CH2F2/O2/Ar plasmas

Highly selective etching of a SiO2 layer using a chemical vapor deposited (CVD) amorphous carbon (a-C) mask pattern was investigated in a dual-frequency superimposed capacitively coupled plasma etcher. The following process parameters of the C4F8/CH2F2/O2/Ar plasmas were varied: the CH2F2/(CH2F2 + O2) flow ratio (Q(CH2F2)), the high frequency power (PHF), and the low frequency power (PLF). It was found a process window exists to obtain infinitely high etch selectivity of the SiO2 layer to the CVD a-C. The process parameters of Q(CH2F2), PHF, and PLF played critical roles in determining the process window for oxide/CVD a-C etch selectivity, presumably due to the disproportionate degree of polymerization on the SiO2 and CVD a-C surfaces.