Adsorption and thermal dissociation of disilane (Si₂H₆) on Si(100)2×1

Adsorption and thermal dissociation of Si2H6 on Si(100)2×1 surfaces has been studied using electron energy loss spectroscopy (EELS) and reflection high-energy electron diffraction (RHEED). Surface reactions were followed by recording the intensities and the positions of EELS peaks associated with dangling bonds on the initial 2×1 surface, surface Si–H bonds, and the appearance of dangling bonds due to Si dimer bond rupture together with the relative intensities of the integral and half-order RHEED diffraction spots. The results indicate that with continued disilane exposure, Si2H6 is dissociatively chemisorbed onto dangling bond sites on Si(100) and the initially adsorbed species (probably SiH3) further dissociate to form a mixed (2×1):H monohydride and (1×1)::2H dihydride surface. The mixed surface is then slowly converted to a (1×1)::2H surface through further reactions with Si2H6. While the Si(100)2×1 dangling bonds were saturated at Si2H6 doses of ≂5×1015 cm−2, much higher doses (≂2×1017 cm−2) were required to obtain a dihydride-saturated surface. Saturated (1×1)::2H surfaces were annealed to successively higher temperatures Ta for 15 s each. At Ta=655 K, hydrogen was evolved leading to the reestablishment of a mixed (2×1):H+(1×1)::2H surface. Most of the remaining dihydride was converted to monohydride at temperatures between 705 and 725 K. The 2×1 dangling-bond EELS peak reemerged at Ta=765 K and the clean-surface 2×1 EELS spectrum, signaling the evolution of the remaining H from the new epitaxial Si layer, was obtained after annealing at 955 K. Implications of these results for Si growth by atomic-layer epitaxy is discussed.