ATOMIC LAYER ETCHING OF SILICON BY THERMAL-DESORPTION METHOD

Atomic layer etching of Si has been realized by modulating the substra te temperature synchronized with chlorine gas irradiation. This is bas ed on the surface chemistry wherein chlorine atoms adsorbed on the cle an Si surface at room temperature are thermally desorbed as SiCl2 over 650 degrees C. For Si(111) substrates, the etching rate R was saturat ed at about 3/7 monolayer per cycle for the peak temperature of more t han 675 degrees C. The saturated etching rate corresponds to half the number of rest atoms of the Si(111) 7 x 7 surface. The chlorine dosage for the saturation was about 3.5 m Torr x 4 s. The experimental resul ts agreed well with the theoretical estimations based on the desorptio n kinetics of SiCl2. The increase of the surface roughness by etching was less than one monolayer.