Ultrahigh selective etching of SiO₂ using an amorphous carbon mask in dual-frequency capacitively coupled C₄ F₈ / CH₂ F₂ / O₂ /Ar Plasmas

Highly selective etching of a silicon dioxide layer using a very thin physical-vapor-deposited amorphous carbon layer (PVD-ACL) was investigated in a dual-frequency superimposed capacitively coupled plasma etcher. The following process parameters of the C₄ F₈ / CH₂ F ₂ / O₂ /Ar plasmas were manipulated: CH₂ F ₂ / (CH₂ F₂ + O₂) flow ratio, high frequency (HF) power (PHF), and low frequency power (PLF). A wide processing window existed to produce the ultrahigh etch selectivities of a SiO₂ layer using the patterned PVD-ACL mask. The etch gas flow ratio played a critical role in determining the process window for ultrahigh silicon oxide/ ACL etch selectivity due to the disproportionate change in the degree of polymerization on the SiO₂ and ACL surfaces. Etching of the ArF photoresist/bottom antireflective coating (BARC)/ SiO_x /ACL/silicon-oxide-stacked structure allows the use of a very thin PVD-ACL as an etch mask layer for the etching of high aspect ratio silicon dioxide patterns.