Quantum chemistry calculations of the reactions of gaseous oxygen atoms with clean and adsorbate-terminated silicon(100)-(2x1)

Reactions of gas-phase radicals at solid surfaces are fundamental to the plasma-assisted processing of semiconductor materials. In addition to adsorbing efficiently, radicals incident from the gas-phase can also stimulate several types of elementary processes before thermally accommodating to the surface. Reactions that occur under such conditions may be classified as non-thermal; and examples include atom insertion, direct-atom abstraction and collision-induced reaction and desorption. Indeed, non-thermal surface reactions play a critical role in determining the enhanced surface reactivity afforded by plasma processing. Advancing the fundamental understanding of radical-surface reactions is therefore of considerable importance to improving control in plasma-assisted materials processing. Our study used quantum chemical calculations to investigate the interactions of gas-phase oxygen atoms [O(3P)] with clean and adsorbate-modified Si(100)-(2 x 1) surfaces. We carefully studied reaction pathways for the oxygen insertion, adsorbate abstraction and adsorbate migration of these species on reaction with O(3P) using density functional theory (DFT) and silicon clusters. Knowledge of these reaction pathways helps determine the viability of certain reactions on Si(100)-(2 x 1) by gas-phase oxygen atoms in plasma-assisted material processing in general.; Another goal of our study was to better understand the chemistry of certain ultrathin silicon-based films. Silicon dioxide has been at the center of the microelectronics industry given its multiple electrical properties. However, as the size of the devices keeps shrinking according to Moore's law predictions of number of transistors, the demands imposed on this material necessitate a detailed understading of its chemistry at the molecular level urging researchers to look for several alternatives. Materials such as silicon oxynitride (SiO xNy) and silicon oxycarbide (SiO xCy) have been suggested as possible silicon dioxide substitutes as gate dielectric and interface dielectric, respectively. Silicon oxynitride can be obtained by either inserting nitrogen atoms into silicon dioxide or oxygen atoms into a silicon nitride film, resulting in ultrathin layers that enhance properties of pure silicon dioxide as a gate dielectric. Silicon oxycarbide is one of the products that evolved as an alternative far silicon dioxide as a result of the recent trend of organic functionalization of the silicon surfaces (a process by which hydrocarbon molecules are chemisorbed on tap of the silicon surfaces to combine the semiconductor properties of silicon with the organic functionality of carbon). Thus we used quantum chemistry calculations to study the initial steps of oxidation of the clean Si(100)-(2 x 1) surface, of the abstraction of nitrogen atoms, and for insertion of gaseous oxygen atoms on acetylene- and ethylene-terminated Si(100).