Atomic layer etching of Si has been realized by modulating the substrate temperature synchronized with chlorine gas irradiation. This is based on the surface chemistry wherein chlorine atoms adsorbed on the clean Si surface at room temperature are thermally desorbed as SiCI2 over 650°C. For Si(lll) substrates, the etching rate R was saturated at about 3/7 monolayer per cycle for the peak temperature of more than 675°C. The saturated etching rate corresponds to half the number of rest atoms of the Si(lll) 7x7 surface. The chlorine dosage for the saturation was about 3.5 mTorr x 4 s. The experimental results agreed well with the theoretical estimations based on the desorption kinetics of SiCI2. The increase of the surface roughness by etching was less than one monolayer.
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