Kinetic Study of the Thermal Crystallization Behavior of Hydrogenated Amorphous Silicon Prepared by ECRCVD

摘要

Hydrogenated amorphous silicon (a-Si:H) thin films were deposited at low temperature by electron cyclotron resonance chemical vapor deposition (ECRCVD). A furnace annealing (FA) treatment was applied to the as-grown thin films to initiate solid-phase crystallization (SPC) in nitrogen atmosphere and oxygen atmosphere. Raman spectroscopy and X-ray diffraction (XRD) were used to investigate the crystallization and grain growth behaviors in the annealed films in N_2. The crystalline fraction of the annealed films can reach ~80%, and a grain size of up to 17 nm can be obtained from the FA treatment at high temperatures. The surface morphologies and microstructures of annealed films were observed using transmission electron microscopy (TEM). The evolution of crystallization with the nucleation and grain growth processes in the annealed film was described by classical thermal kinetics. The activation energies for the incubation time and grain growth of the ECRCVD film were 3.51 ± 0.09 eV and 2.54 ± 0.13 eV, respectively. The results indicate that the ECRCVD deposited films exhibited more voids which would lead to lower nucleation barrier for crystallization and faster rate for grain growth when compared to other different fabrication methods. This was also the reason for the ease of grain growth. Furthermore, the chemical states of silicon in thermally oxidized a-Si:H films were examined by X-ray photoelectron spectroscopy (XPS). The crystalline fraction of annealed films in oxygen atmosphere is higher than that of film in nitrogen atmosphere due to the Si daggling bonds easily form bonding reaction with O atoms for the amorphous phase in oxygen atmosphere. Overall this study provided not only a better understanding of crystallization kinetics in ECRCVD-grown a-Si:H films in N_2 vs. O_2 atmosphere but also this investigation provided a good understanding on the enhancing effect of crystallization behavior related to mechanism and characteristics of ECRCVD-grown a-Si:H films being oxidized at high annealing temperatures.