UV Photostimulated Si Atomic-Layer Epitaxy

Abstract

ABSTRACTSingle-crystal Si films have been grown on Si(001)2×1 substrates by UVphotostimulated atomic-layer epitaxy (ALE) from Si2H6. The ALE deposition rate R per growth cycle remains constant at 0.4 monolayers (ML) over a wide range of deposition parameters: growth temperature (Ts= 180–400 °C), Si2H6 exposure (peak pressure during gas pulse = 0.1−5 mTorr), laser energy density ( = 250–450 mJ cm−2 where is determined by Ts), and number of UV laser pulses per cycle. A film growth mocrel, based upon the results of the present deposition experiments and Monte Carlo simulations, together with our previous adsorption/desorption measurements, Is used to describe the reaction pathway for the process. The Hterminated silylene-saturated surface formed by adsorption and desorption of disilene is thermally stable and passive to further Si2H6 exposure. ArF or KrF laser pulses (≅20 ns) are used to desorb H, following a Si2H6 exposure, and the growth cycle is repeated until the desired film thickness is obtained. At Ts < 180 °C, the growth process becomes rate limited by the surface dissociation step and R decreases exponentially as a function of 1/Ts with an activation energy of ≅0.5 eV. At Ts > 400 °C, H is thermally desorbed and pyrolytic growth competes with ALE. Transmission electron micrographs together with selected-area electron diffraction patterns show that the ALE films are epitaxial layers with no observed extended defects or strain.