Ab initio molecular-orbital theory is used to unravel the mechanism of HF etching leading to hydrogen-passivated silicon surfaces as observed experimentally. Total-energy calculations on transition states of model silicon compounds suggest that the activation barriers for HF attack of the Si surface determine the resulting surface termination. In particular, the H passivation results from efficient removal of fluorine-bonded surface silicon as ${\mathrm{SiF}}_4$ leaving behind hydrogen.

• Received 20 February 1990

DOI:https://doi.org/10.1103/PhysRevLett.65.504