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

Abstract

Selective etching of SiO 2 over polycrystalline silicon has been studied using CHF 3 in an inductively coupled plasma reactor ͑ICP͒. Inductive powers between 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 dioxide, silicon, and passively deposited fluorocarbon films. Using in situ ellipsometry, the etch rates for all three of these materials were obtained for a self-bias voltage of Ϫ85 V, as well as passive deposition rates of fluorocarbon films. X-ray photoelectron spectroscopy has been used to examine the composition of steady-state fluorocarbon films present on the surfaces of polycrystalline silicon, and silicon dioxide during etching at high and low inductive powers. The dependence of the silicon etching behavior is shown to be clearly linked to the fluorocarbon polymerization and etching behavior. Thus, the polymerization and etching behavior of the fluorocarbon is the overwhelming parameter that governs the etch selectivity process within the ICP. Selectivities of oxide to silicon are determined to increase with the inductive power, and are found to be the highest at the intermediate pressure of 10 mTorr. While the stoichiometry of the fluorocarbon films are critical factors in determining the overall etch rate behavior, the fluorocarbon film thickness on the polycrystalline and crystalline silicon is the dominant factor in determining the SiO 2 over silicon etch selectivity. The mechanisms involved in attaining high selectivity are dominated by a defluorination of the fluorocarbon steady-state film on polycrystalline silicon, while maintaining a high ion current to the wafer.

Differences in erosion mechanism and selectivity between Ti and TiN in fluorocarbon plasmas for dielectric etch

“…These changes can be explained by a higher degree of collision processes in the plasma at high pressures leading to a lower degree of ionization of Ar and a higher degree of dissociation of CF 4 . 26,29,33 Similar trends were observed when the relative amount of FC feed gas in the CF 4 /Ar discharge [ Fig. 5(c)] was increased.…”

“…As discussed previously, extraction of the FC thickness from this model was not possible due to significant thickness fluctuations of the SiO 2 layer underneath the TiN film (61.5 nm) as determined with transmission electron microscopy. 6 However, due to the similarity in optical properties of the FC layer (Ñ ¼ 1.420 -0i) 29 and SiO 2 (Ñ ¼ 1.457 -0i), extracted ER during steady-state erosion of TiN remained unaffected. 6 …”

Study of Ti etching and selectivity mechanism in fluorocarbon plasmas for dielectric etch

“…23) and SiO 2 (Ñ ¼ 1.457-0i) are almost identical. This model is set up in a similar fashion as the previously described model, but it simulates a FC film on top of the Si/SiO 2 /Ti stack instead of TiO 2 .…”

Optical Fibre on a Silicon Chip

“…The fluorocarbon film reacts with silica in the presence of ion bombardment to form a volatile SiF 4 . To increase the etch rate of silica and improve mask selectivity, the ionic current density, ionic energy, and F/C reactive ion species are required not only to be boosted [36 ] but also independently controlled. Inductively coupled plasma (ICP) reactive ion etching system can fulfill these requirements.…”