Damage induced in Si by ion milling or reactive ion etching

Surface damage in Si substrates created by Ar-ion milling or by reactive-ion etching in CF₄, CHF₃, Cl₂, SiCl₄, or SiF₄ has been investigated. Metal-oxide- semiconductor capacitors were fabricated on the etched Si substrates, and the interface-state densities were obtained from capacitance-voltage measurements. Interface states generated by the dry etching processes were strongly dependent on the etching gas and the bias voltage. Carbon-based gases (CF₄, CHF₃) induced more interface states than those without carbon. For the carbon-based gases, Si samples etched in CHF₃ showed lower densities of interface states than samples etched in CF₄ under the same conditions. Generation lifetime measurements indicated that samples with large densities of interface states also had short lifetimes. Measurements of oxidation-induced stacking faults caused by dry etching were consistent with both the interface-state and lifetime measurements. Thermal annealing of the etched wafers was not effective in reducing the surface damage. The measured interface states on the dry etched Si substrates could be lowered to their pre-etched levels by removing at least 500 Å of the etched surface by wet chemical etching.