LOW-TEMPERATURE HETEROEPITAXIAL GROWTH OF SI1-XGEX-ON-SI BY PHOTO-ENHANCED ULTRA-HIGH-VACUUM CHEMICAL-VAPOR-DEPOSITION USING SI2H6 AND GE2H6

Strained-layer Si1-xGex-on-Si heteroepitaxy has been achieved by photolytic decomposition of disilane (Si2H6) and digermane (G e(2)H(6)) in an ultra high vacuum (UHV) chamber at substrate temperatures as low as 275 degrees C. An ArF excimer laser (193 nm) shining parallel to the Si substrate was used as the UV light source to avoid surface damage and substrate heating. The partial pressures of the source gases in the reactor were chosen to vary the Ge mole fraction x from 0.06 to 0.5 in the alloy. The Si2H6 partial pressure was kept at 10 mTorr and the Ge2H6 partial pressure was varied from 0.13 to 2 mTorr with the laser intensity fixed at 2.75 x 10(15) photons/cm(2) pulse. To fit the Si1(-x)Ge(x) growth rate and Ge mole fraction data, the absorption cross section of Ge2H6 at 193 nm was set to 1 x 10(-16) cm(-2), which is 30 times larger than that of Si2H6 (3.4 x 10(-18) cm(2)). For Si1-xGex alloy growth, the deposition rate of Si increases with Ge mole fraction, resulting in increased Si1-xGex alloy growth rates for higher Ge content. The increase of the Si growth rate was attributed to the enhanced adsorption rate of Si2H6 pyrolytically in the presence of Ge, rather than due to photolytic decomposition reaction. The Ge mole fraction in Si1-xGex alloys can be predicted by a new model for Si and Ge pyrolytic and photolytic growth. The model describes the increased growth rate of Si1-xGex alloys due to a Ge2H6 catalytic effect during photo-enhanced chemical vapor deposition.