Low-Temperature and High-Speed Fabrication of Nanocrystalline Ge Films on Cu Substrates Using Sub-Torr-Pressure Plasma Sputtering

We fabricated nanocrystalline Ge films using radio-frequency (RF) magnetron plasma sputtering deposition under a high Ar-gas pressure. The Ge nanograins changed from amorphous to crystalline when the distance between the Ge sputtering target and the substrate was decreased to 5 mm and the RF input power was 11.8 W/cm ² (60 W), where the deposition rate was as high as 660 nm/min. In addition, the size of the nanocrystalline grains increased from 100 to 307 nm when the RF input power for plasma production was increased from 11.8 W/cm ² (60 W) to 17.7 W/cm ² (90 W). In the developed narrow-gap plasma process at sub-Torr pressures, nanocrystalline Ge films were successfully fabricated on Cu substrates at low temperatures, without the substrate being heated. However, when annealing was conducted under an N ₂ atmosphere, which is the conventional method to induce solid-phase crystallization, the amorphous Ge layer on a Cu substrate changed to a Cu ₃ Ge crystal layer through interdiffusion of Ge and Cu atoms at 400–500 °C.