Ion-enhanced etching of Si(100) with molecular chlorine: Reaction mechanisms and product yields

Laser single-photon ionization time-of-flight mass spectrometry is used to measure silicon etch products that evolve during argon ion-enhanced etching of room temperature Si(100) with molecular chlorine over an ion energy ran ge of 275-975 eV. The etch products are examined as a function of ion energ y, ion flux, and molecular chlorine flux. The neutral Si atom, SiCl, and Si Cl2 are the only product species observed with the 118 nm ionization and ar e detected directly without fragmentation. The Si and SiCl species are the main products, with the latter having much greater yield. The yield of each product increases with increasing ion energy. The SiCl/Si yield ratio incr eases with decreasing ion kinetic energy, indicating an increase in the chl orine surface coverage at lower ion energies. A simple kinetic model, inclu ding chlorine adsorption and sputtering of the resulting silicon chloride s urface moieties, is proposed to describe the formation of Si and SiCl etch products. A model describing the chlorine pressure dependence of Si atom sp uttering is developed in which the sputtering of Si atoms occurs from two d ifferent precursor states, one from an unchlorinated site and another from a partially chlorinated site. Using this kinetic model, the sputtering yiel d for SiCl per Ar+ is estimated from the molecular chlorine flux dependence of the SiCl signals and ranges from 3.2+/-0.8 to 4.9+/-0.9. (C) 1999 Ameri can Vacuum Society. [S0734-2101(99)01406-2].