Etching of Si surfaces with hot chlorine beams: Translational and vibrational excitation of the incident chlorine particles

Abstract

A systematic study of etching of Si(100) and Si(111) and Ar+ bombarded Si(100) (surface with defect sites) with chlorine has been carried out. We have compared the reactivity of atomic and molecular chlorine, and studied the effect of translational and vibrational excitation of the etchant on the etch rate. Similar etch rates were obtained on the Si(100) and Si(111) single crystal surfaces. On both surfaces the major etch products were SiCl4 at Ts<500 K and SiCl2 at Ts≳600 K. Some SiCl desorption was obtained at Ts≳1100 K. We have outlined the conditions under which the etch rate, at constant incident flux, is adsorption and desorption limited. On the Si(100) and Si(111) surfaces we found that when the etch rate is reaction limited, higher etch rate can be obtained with atomic chlorine than with molecular chlorine. In the adsorption limited regime, translational excitation of both atomic and molecular chlorine results in a higher etch rate than that obtained with slow atomic and molecular chlorine. Vibrational excitation of Cl2 does not result in an enhancement of the etch rate on the single crystal surfaces studied. In the desorption limited regime the etch rate is primarily determined by the surface temperature. The nature of the etchant particles does not have a significant effect. On Ar+ bombarded Si(100), we obtained a small increase in the etch rate with translationally and vibrationally excited Cl2, and comparable enhancement is obtained with Cl2 that is only translationally excited. The difference in the etch properties of the single crystalline and Ar+ bombarded silicon surfaces points to the importance of surface defects in etching. The present results show that at room temperature the low etch rate of silicon single crystal surfaces with chlorine, as compared to etching with fluorine, is due to the low formation rate of volatile surface products.