Selective Plasma Etching for High-Aspect-Ratio Oxide Contact Holes

The effects of pressure and CH2F2 percentage on the selectivity of oxide to photoresist (oxide:PR) and on reactive ion etch (RIE) lag in a helicon wave high-density CF4/CH2F2 plasma are reported. Operating the helicon source in high-pressure (20–30 mTorr) fluorocarbon and hydrofluorocarbon plasmas results in highly selective oxide etching. By independently controlling the formation rate of depositing polymer precursors, RIE lag effects can be minimized. Plasma and spectroscopic data suggest a correlation between the polymer deposition rate, high oxide:PR selectivity, and reduced RIE lag. An explanation for the results, based upon operation in a downstream mode combined with collisional sheath effects and isotropic polymer deposition, is proposed.