Potentialities of disilane for the low temperature epitaxy of intrinsic and boron-doped SiGe

Abstract

The disilane (Si2H6)+germane (GeH4) chemistry has been evaluated for the reduced pressure (2660Pa, i.e. 20Torr), low temperature growth of intrinsic and heavily boron-doped SiGe. A SiGe growth rate “plateau” has been evidenced between 650°C and 750°C. Meanwhile, the Ge concentration x was rather steady in the 500°C–700°C range. A linear increase of the SiGe growth rate with the GeH4 flow occurred at 500°C, 550°C and 675°C. The increase of x with the GeH4 mass-flow otherwise changed from linear to sub-linear as the growth temperature was reduced from 675°C down to 500°C–550°C. Be it with Si2H6 or SiH4, the SiGe growth rate fell by a factor of ~7–8 when switching from 550°C to 500°C. For the same x, growth rate was nevertheless 3–9 times higher with Si2H6 than with SiH4. We have also studied the impact of B2H6 on the 500°C growth kinetics of SiGe with Si2H6. Large substitutional boron concentrations were obtained in single-crystalline SiGe:B layers: [B]subst.~3.7×1020 cm−3. Surface B atoms otherwise catalysed H desorption, resulting in growth rates ~5 times higher for SiGe:B than for intrinsic SiGe. Finally, a monotonic decrease of the SiGe(:B) growth rate together with a significant increase of the Ge concentration were evidenced at 500°C and 675°C when adding HCl to the gaseous mixture. At 500°C, SiGe:B growth rates still stayed 3 times higher than the intrinsic SiGe ones. Adding HCl had otherwise no clear impact on [B]subst.