Layer-by-layer etching of Cl-adsorbed silicon surfaces by low energy Ar+ ion irradiation

Layer-by-layer etching of Si(1 0 0) has been investigated by alternating chlorine adsorption and Ar+ ion irradiation. As the Ar+ ion source, a helicon plasma has been used to invoke the surface reaction of Si with the adsorbed chlorine. At a chlorine partial pressure of 10 mPa, the Si surface was found to be fully saturated with adsorbed chlorine in 20 s. In order to achieve the layer-by-layer etching of Si, the Ar+ ion acceleration energy should be above 20 eV at the time of chlorine adsorption. At energies above 40 eV, however, sputtering of Si was found to occur. The self-limited etch rate was measured to be half monolayer per cycle, which was 0.68 Å per cycle. The roughness of Si surface was found to increase during the etching by about 22% after 900 cycles.