High Rate Growth of Highly-Crystallized Ge Films on Quartz from VHF Inductively-Coupled Plasma of GeH₄ + H₂

We have studied uniform growth of crystalline Ge films on quartz plate from VHF (60MHz)-ICP of 10% GeH4 diluted with H2 in the temperature range from 150 to 350ºC. By optimizing total gas flow rate, gas pressure, VHF power and antenna-substrate distance, the growth rate as high as 7.4nm/s was obtained at 150ºC and increased gradually up to ~7.9nm/s at 350ºC. The crystallinity, which was evaluated by Raman scattering measurements as an integrated intensity ratio of TO phonons in crystalline phase to those in disordered phase, reached a value as high as ~93 % at 350ºC, but degraded down to 64% at 150ºC as a result of the formation of a 60~70nm-thick amorphous incubation (A. I.) layer on quartz. By applying a two-step deposition method at 150ºC, in which the GeH4 concentration was selected to be 0.6% for the crystalline nucleation in the first 10s deposition, being as thin as 10nm in thickness, and then changed to 10% GeH4 for the high rate growth, the crystallinity was improved to 78% with keeping an effective growth rate as high as 7.5nm/s, because of a significant increase in the growth rate after the crystalline nucleation.