Mechanism of ion-assisted etching of silicon by fluorine atoms

Abstract

The mechanism for the anomalous increase in etch rate when an ion beam is coincident on a semiconductor surface with an etchant species, such as fluorine, is explored with the use soft X-ray photoemission. A Si(111) surface was exposed to a sufficient amount of XeF2 to reach the steady state reaction regime, and photoemission spectra of the reaction layer remaining on the surface were collected. The surface was then treated to incremental doses of 500 eV argon ions, and photoemission spectra were collected after each dose. The results showed that the ion beam tended to drive a disproportionation reaction in which SiF3 species were converted into SiF2 plus SiF4. The SiF4 molecules then desorbed from the surface as the major reaction product. Since it is this conversion of SiF3 into products that is the rate limiting step in the reaction, the ion beam thus effects a kind of chemical sputtering, in which sufficient energy is added by the ion beam to induce a chemical reaction to occur. © 1987 Elsevier Science Publishers B.V.