A COMPARATIVE-STUDY OF THE INITIAL OXYGEN AND WATER REACTIONS ON GERMANIUM AND SILICON USING SIMS

The initial reactions of oxygen and water with amorphised Ge(100) and Si(100) surfaces at room temperature were investigated using the SIMS (secondary ion mass spectrometry) technique, The intensities of both p ositive and negative secondary ion species were recorded as a function of oxygen or water pressure (in the range 10(-9) to 5 x 10(-6) mbar) under dynamic dosing conditions. The high power law relationships and secondary ion yields show that Si is more reactive than Ge to initial corrosion by oxygen and water in the pressure range studied. For the o xygen reaction, this increased reactivity is explained by the observat ion that oxygen adsorbs in a molecular precursor state, and the activa tion energy for subsequent dissociation is higher for Ge than for Si. Water dissociates to H and OH species on both the Ge and Si surfaces. The water reaction on Si is less rapid than the oxygen reaction since the Si-H species formed inhibit the formation of the SiO2 corrosion ph ase due to a site-blocking effect. The Ge-H species, however, appears to be less stable and does not inhibit the oxidation of Ge. Since Ge i s significantly less reactive than Si, the GeO2 corrosion phase does n ot start to form in the pressure range studied (< 5 x 10(-6) mbar) for both oxygen and water pressure.