Structure and crystallization of low-pressure chemical vapor deposited silicon films using Si2H6 gas

Abstract

Microstructures of silicon films deposited on SiO2 substrates by low-pressure chemical vapor deposition using Si2H6 gas were investigated and compared to those using conventional SiH4 gas by transmission electron microscopy and x-ray diffraction. The deposition rate of the Si2H6 process was about ten times higher than that of SiH4 process at low temperatures (<550 °C). The transition deposition temperature from amorphous to polycrystalline film was found to be around 580 °C, which was similar to that of the SiH4 process. The film deposited at 600 °C was partially crystalline and had equi-axed grains with the largest average grain size of 0.3 μm while the films using SiH4 has needle-like columnar grains with smaller sizes (200 Å). The x-ray diffraction analysis showed that the structural disorder to amorphously deposited Si films increases as deposition temperature decreases. The grain size in the film after crystallization at 600 °C strongly depended on the deposition temperature and the deposition rate, producing a larger grain size at a lower deposition temperature and/or at a higher deposition rate (Si2H6 deposition compared to SiH4 deposition). The apparent increase in grain size can be explained as a result of the lowered number of crystal nuclei due to a decrease in the number of pre-existing microcrystallites serving as heterogeneous nucleation seeds. When the deposition rate was lower than the critical value (approximately 2–4 nm/min), the grain size in the crystallized film decreased for both SiH4 and Si2H6 films. The maximum grain sizes were 4.5 and 0.3 μm at the deposition temperatures of 485 and 550 °C for the films using Si2H6 and SiH4 gases, respectively.