Reaction kinetics in synchrotron-radiation-excited Si epitaxy with disilane. I. Atomic layer epitaxy

Abstract

We investigated the mechanism of silicon crystal growth mediated by a surface photochemical reaction. The growth process consists of reactive sticking of disilane (Si2H6) onto a partially hydrogen covered surface followed by the photon-stimulated desorption of hydrogen atoms and consequent regeneration of dangling bonds. The saturation coverage of Si admolecules resulting from self-limiting chemisorption of disilane was found to be 0.42 monolayer (ML), and the ejection of H+ and H+2 ions was observed by time-of-flight mass spectroscopy. Hydrogen removal by the purely electronic process differs from thermal desorption, however, in that not all of the hydrogen is removed. Analysis of film growth by repetition of the cycle of disilane exposure, evacuation, and synchrotron radiation irradiation showed that the onset temperature of thermal growth (350 °C) is the same as that of H2 desorption from the dihydride species. Below 350 °C a digital growth of 0.18 ML/cycle occurs over a wide range of gas exposure times, irradiation times, substrate temperatures, and the irradiation intensities. If the temperature is raised to facilitate thermal desorption of hydrogen atoms and migration of Si adatoms, the number of Si adatoms delivered in each cycle increases significantly. Photolytic, thermal, and photothermal effects result in growth rates of 0.4 ML/cycle at 430 °C and 1 ML/cycle 480 °C.