Laser-enhanced epitaxy of Si and Si-Ge: Microelectronics Research Center, University of Texas at Austin, Austin 78712, TX, USA

Abstract

This paper discusses low temperature Si homoepitaxy on Si (100) substrates by the photolytic decomposition of Si 2H 6 by the 193 nm emission of an ArF excimer laser in a photo-enhanced chemical vapor deposition (PCVD) system. The growth involves photolytic decomposition of Si 2H 6 and the generation and adsorption of SiHSiH 3 precursors on the hydrogenated Si surface. PCVD of Si was achieved in two ways: with the laser passing parallel to the substrate or directly incident on it. For parallel laser incidence, controllable deposition rates of 0.5–4 A min −1 were achieved. Epitaxial films were achieved at temperatures as low as 250 °C using photon flux densities of 10 16 photons pulse −1 cm −2, and Si 2H 6 partial pressures of 20 mTorr. For parallel incidence, very low defect density films in terms of stacking faults and dislocation loops (less than 10 5 cm −2), and excellent crystallinity have been grown at 250 °C and low laser power, as confirmed by Schimmel etching and Nomarski microscopy, transmission electron microscopy (TEM), electron diffraction and in situ reflection high energy electron diffraction (RHEED). The growth rates were observed to be linearly dependent on laser power. For direct laser incidence, very high growth rates (20–80 A min −1) were obtained. Single crystal films with a growth rate of ~ 20 A min −1 were obtained at a photon flux density of 7 × 10 14 photons pulse −1 cm −2 at 300 °C and 20 mTorr Si 2H 6 partial pressure. Boron doping with abrupt doping transitions has been achieved in the low temperature epitaxial films by introducing B 2H 6 during the process. Phosphorus doping has been achieved using PH 3. Epitaxial Si 1− x Ge x films using Si 2H 6 and Ge 2H 6 have been achieved. Si/Si 1− x Ge x heterostructures with sharp Ge transitions have been grown by exploiting the low temperature capability of the PCVD process.