ROOM-TEMPERATURE WATER-ADSORPTION ON THE SI(100) SURFACE EXAMINED BY UPS, XPS, AND STATIC SIMS

The adsorption of water on the reconstructed Si(100)-(2 c 1) surface a t room temperature is studied using an integrated multi-technique appr oach. UPS, XPS, and static SIMS surface examination in a variable temp erature mode of experimentation indicates dissociative adsorption of w ater to hydroxyl (OH) and hydride (H) groups saturating the single dan gling bonds on adjacent dimer-pair Si atoms of the reconstructed surfa ce. No evidence of molecular water is found. Upon heating the surface the hydroxyl decomposes to bridge-bonded oxygen (Si-O-Si) and addition al silicon hydride groups. This is complete at approximately 400-degre es-C. Above 400-degrees-C the surface loses hydrogen, presumably as H- 2, and above 600-degrees-C the substoichiometric silicon oxide sublime s as SiO to return to the clean, reconstructed surface. The chemical s tate of oxygen on the surface is monitored as a function of temperatur e through the use of a DELTA parameter (DELTA = binding energy O(1s) - binding energy Si(2p)). These results are consistent with experimenta l evidence and surface chemistry first proposed by others. Assignment of the observed DOS features is made by comparison of the experimental DOS spectra to calculations for the system and for system analogs (Si OH radical, oxygen-saturated Si surface, hydrogen-saturated Si surface ), and to another hydroxyl system (NaOH). Four major features of the s aturated hydroxyl/hydride surface are found: 5 eV Si-H bond, Si sp3 H 1s character; 6.4 eV O 2p lone pair, pi symmetry nonbonding orbital; 7.6 eV O-H bond, O 2p + H 1s character, sigma symmetry; 11.9 eV Si-OH bond, sp3 + O 2p character (binding energies relative to the Fermi le vel).