The Study Of Fabrication Of Si-based Crystalline SiCN Films

Silicon carbon nitrogen(SiCN),with an adjustable band gap between 2.86 and 5.0 eV,is considered as a candidate material for advanced blue or ultraviolet optoelectronic devices.The most SiCN films are amorphous,although the crystalline SiCN films have also been reported.Considerable attempts for improving crystallization,controlling composition and exploring mechanism have been continually reported.At first,a new method has been developed for fabricating crystalline SiCN thin films.The SiCN film has been formed on carbonized Si(111)via a constant-source diffusion process in a chemical vapor deposition(CVD)system.Second,with the unique compositional structure,the crystalline SiCN film has been applied as the buffer layer for the 3C-SiC epilayer on the Si(111)substrate.In the end,the SiCN film has been fabricated on Si(111)via a thermal diffusion process.The main results are listed as follow:(1)The crystalline SiCN film,which has the same crystal structure as 3C-SiC verified by X-ray diffraction and Raman scattering,has been formed on carbonized Si(111)substrate by constant-source diffusion using a chemical vapor deposition system.Via X-ray photoelectron spectroscopy,the film has been identified as the mixture of elemental Si and SiC1-?N? alloy.The measured composition distribution can be well explained by the constant-source difusion model,confirms that the formation mechanism of the SiCN film is the diffusion of C and N into the Si substrate.This provides a new method for fabricating crystalline SiCN thin films.(2)Cubic silicon carbide(3C-SiC)has been grown on Si(111)substrate by chemical vapor deposition.The crystal quality of SiC with the SiCN buffer layer is obviously improved compared with that grown on the SiC buffer layer formed by carbonization of Si(111)substrate.This in-situ formed SiCN film evolves into the SiCN buffer layer including the SiC1-?N? alloy layer and SiCN composite layer,during the 3C-SiC high temperature growth.The SiCN buffer layer,with two sub layer structure of the SiC1-?N? alloy layer and SiCN composite layer,can intensively accommodate the lattice mismatch between SiC and Si and effectively lead to improvement for 3C-SiC(111)growth.(3)The evolution of the crystal quality,the surface morphology of the 3C-SiC film and the stress in the crystal has been investicated.With the increase of growth time,the crystal quality of the 3C-SiC film is improved;the surface roughness of the film decreases from 34.28 nm to 21.33 nm,and the film shifted from in-plane biaxial compressive strain state to in-plane biaxial tensile strain state.The in-plane compressive stress in 3C-SiC has been produced in the initial stage due to lattice mismatch between SiC and SiC1-?N? alloy layer.As a result,the film shifted from in-plane biaxial compressive strain state to in-plane biaxial tensile strain state and can effectively reduce the in-plane tensile stress.(4)The crystalline SiCN film,which has the same crystal structure as 6H-SiC verified by X-ray diffraction and Raman scattering,has been fabricated on Si(111)via a thermal diffusion process.The SiCN composite layer,in the crystalline SiCN film,is formed due to the diffusion of C and N into the Si substrate.The SiC1-?N?alloy layer is formed by N out-diffusion from the SiCN composite layer and C in-diffusion towards the substrate.