A Benchmark of Germane and Digermane for the Low Temperature Growth of Intrinsic and Heavily in-situ Boron-Doped SiGe

Abstract

We have benchmarked germane and digermane for the low temperature growth of SiGe and SiGe:B (with disilane as the Si gaseous precursor). At 500°C, 20 Torr, the SiGe growth rate increased linearly with the Ge flow. It was 8 to 10 times higher with Ge2H6 than with GeH4, however. Ge atoms were otherwise 4 times more likely to incorporate in SiGe films with Ge2H6 than with GeH4. The use of GeH4 led to an exponential increase of the 20 Torr SiGe growth rate with temperature (42 kcal. mol.-1 activation energy), together with a slight linear decrease of x. The situation was different with Ge2H6. As T increased, we had a slight exponential increase of the SiGe growth rate (Ea = 15 kcal. mol.-1) and a huge linear decrease of the Ge content. Adding HCl to Si2H6 + Ge2H6 otherwise led at 500 °C, 20 Torr to a significant decrease of the growth rate, together with a significant Ge concentration increase. Finally, we have investigated the 500°C, 20 Torr growth of SiGe:B layers (with a Si2H6 + Ge2H6 + B2H6 chemistry). A marked increase of the SiGe:B growth rate with the B2H6 flow was observed, together with a less than linear decrease of the Ge concentration. The lowest resistivity, e.g. 4.3x10-4 Ω.cm, was obtained for F(B2H6)/F(H2) = 2.5x10-6. For higher B2H6 flows, we had a resistivity re-increase, which was likely due to the crystalline quality degradation then the transformation into poly-SiGe:B evidenced in X-Ray Diffraction.