STRUCTURE AND CRYSTALLIZATION OF LOW-PRESSURE CHEMICAL VAPOR-DEPOSITED SILICON FILMS USING SI2H6 GAS

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-degrees-C). The transition deposition temperature from amorphous to polycrystalline film was found to be around 580-degrees-C, which was similar to that of the SiH4 process. The film deposited at 600-degrees-C was partially crystalline and had equi-axed grains with the largest average grain size of 0.3-mu-m while the films using SiH4 has needle-like columnar grains with smaller sizes (200 angstrom). 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-degrees-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-mu-m at the deposition temperatures of 485 and 550-degrees-C for the films using Si2H6 and SiH4 gases, respectively.