Selective etching of SiO2 over polycrystalline silicon using CHF3 in an inductively coupled plasma reactor

Selective etching of SiO2 over polycrystalline silicon has been studied usi ng CHF3 in an inductively coupled plasma reactor (ICP). Inductive powers be tween 200 and 1400 W, as well as pressures of 6, 10, and 20 mTorr were used in this study of the etch rate and selectivity behaviors for silicon dioxi de, silicon, and passively deposited fluorocarbon films. Using in situ elli psometry, the etch rates for all three of these materials were obtained for a self-bias voltage of -85 V, as well as passive deposition rates of fluor ocarbon films. X-ray photoelectron spectroscopy has been used to examine th e composition of steady-state fluorocarbon films present on the surfaces of polycrystalline silicon, and silicon dioxide during etching at high and lo w inductive powers. The dependence of the silicon etching behavior is shown to be clearly linked to the fluorocarbon polymerization and etching behavi or. Thus, the polymerization and etching behavior of the fluorocarbon is th e overwhelming parameter that governs the etch selectivity process within t he ICP. Selectivities of oxide to silicon are determined to increase with t he inductive power, and are found to be the highest at the intermediate pre ssure of 10 mTorr. While the stoichiometry of the fluorocarbon films are cr itical factors in determining the overall etch rate behavior, the fluorocar bon film thickness on the polycrystalline and crystalline silicon is, the d ominant factor in determining, the SiO2 over silicon etch selectivity. The mechanisms involved in attaining high selectivity are dominated by a defluo rination of the fluorocarbon steady-state film on polycrystalline silicon, While maintaining a high ion current to the wafer. (C) 1999 American Vacuum Society. [S0734-2101(99)08105-1].