Structural And Optical Properties Of The SiCN Films

A compound of silicon carbonitride (SiCN) integrates the unique characteristics of SiC and Si3N4, and is of excellent optical, electrical and mechanical properties, such as high hardness, high antioxidant capacity, chemical inertness and wide band gap. It has potential application prospects in superhard coating, optoelectronics, dielectric barrier layer in copper interconnect and micro-electro-mechanical systems. Its characteristic of emitting blue or blue-ultraviolet light makes it to be one of the key research materials which can resolve the international "blue light" problem. And its compatibility with the silicon integrated circuits process makes it to be the preferred materials for optoelectronic integrated circuits. But its compositions, structures and properties are very complex. In this work, SiCN thin films were prepared using two kinds of process (Ar/C2H2/N2mixed gas+polysilicon target, Ar/N2mixed gas+sintered SiC target), and the characteristics of the composition, chemical bonding, crystal structure and photoluminescence were characterized by X-ray photoelectron spectrometry, Fourier transform infrared spectroscopy, X-ray diffraction, ultraviolet-visible spectrophotometer and fluorescence spectrometer. The mutual interactions among the preparation process, composition, microstructure and optical property of the films were analysized. The photoluminescence mechanisms of370nm,400nm and440nm for the SiCN thin films were discussed.Using the density functional theory of first-principles calculations and the CASTEP module of the material calculation software Material Studio5, the structures and optical properties of the constructed β-Si12-nCnN16(n=0,4,6,8,12) supercells based on β-Si6N8crystal structure were calculated. The results show that the lattice constants a, c and cell volume of the calculated supercells become smaller, while their a/c ratio is essentially unchanged when Si atoms are continually replaced by C atoms. These indicate they maintain isotropic shrinkage in the lattice a and c directions. The band structures of the β-Si12-nCnN16(n=4,6,8) supercells are closer to P-Si12N16rather than β-C12N16. The light transmission for β-Si12-nCnN16(n=0,4,6,8,12) structures has a trend of deterioration and their absorption peak wavelengths move to shorter wavelength with the increase of n.The influence of sputtering power on thin film deposition rate, composition, microstructure and optical band gap and its mechanism were studied. With sputtering power increasing, the deposition rate first increases and then decreases, and optical band gap monotonously decreases, and the Si content monotonously increases and the C content monotonously decreases while the N content is essentially unchanged. It is found that Si and C atoms accupy similar sites in the SiCN network. The C-N, N-Hn, C-Hn, C-C,C≡N, Si-H and Si-C bonds were mainly formed in the SiCN films, and a higher sputtering power is in favor of the formation of C=N, Si-H and C-Hn bonds.The influence of C2H2flow rate on thin film deposition rate, composition, microstructure and optical band gap and its mechanism were studied. With C2H2flow rate increasing, the deposition rate sharply increases, and the C content increases while the Si and N contents decrease in the films, and optical band gap monotonously decreases, and Si-C and C-N bonds monotonically increase while Si-H bond obviously decreases. It is found that the increase of C content favors to the formation of the Si-C and C-N bonds and supresses the formation of the Si-H bond. The bondings are not consistent between in the film surface and in the SiCN film, and Si-O, C-C, C-O, C-N, N-Si and C=N network structure is formed in the film surface.The influence of the N2/Ar flow ratio on thin film deposition rate, composition, structure and optical band gap and its mechanism were studied. With the N2/Ar flow ratio increasing, the deposition rate increases, and the N content increases while the Si and C contents decrease in the films, and the surface roughness values of the films increase. It is found that the increase of N content in the SiCN films promotes the formation of Si-N bond, and supresses the formation of C-C, C-Si and N-C bonds. The increase of Si-N bond with higher optical band gap and the decrease of the Si-C, C-C and C-N bonds with lower optical band gap bring about the increase of optical band gap of the SiCN film. The dependence of photoluminescence of the thin films on their compositions and structures were studied. The strong photoluminescence at400nm was observed in the deposited SiCN films, while the strong photoluminescence at370nm and440nm was observed in the annealed SiCN films. The photoluminescences at370nm,400nm and440nm respectively originate SiOx luminescence center, C clusters and the SiC crystal particles in the SiCN films. It is found that the600℃annealing favors to the formation of the SiC crystal particles in the SiCN film, and the emitting light intensity at440nm in the films can be improved by improving the content of the Si-C bond.