Properties of Ge films grown through inductively coupled plasma chemical vapor deposition on SiO₂ substrates

In this study, we investigated the physical and electrical characteristics of Ge polycrystalline films deposited directly onto SiO2 -covered substrates using inductively coupled plasma chemical vapor deposition (ICP-CVD). The pure Ge films that we deposited at a relatively low temperature of 300°C exhibited the same cubic structure, with primarily (111), (220), and (311) orientations identified from X-ray diffraction patterns, as those deposited at 400°C. The use of such a low temperature not only prevented the plasma window of the chamber from overheating but also allowed crack-free, thicker films to be deposited more easily. The ability to deposit Ge films on SiO2 was closely linked to the hydrogen etching effect, as evidenced by the results obtained using X-ray photoelectron spectroscopy. Although the crystalline characteristics of the low-temperature as-deposited Ge films were somewhat poorer than those obtained at 400°C, subsequent furnace annealing and rapid thermal annealing with a SiNx capping layer improved the crystalline quality significantly. These results, taken together with studies of the surface morphologies and dopant activation of the recrystallized Ge films, suggest that ICP-CVD might be a simple, powerful and reliable approach for the fabrication of polycrystalline Ge thin film transistors.