Synthesis And Characteristic Studies Of Silicon Nitride Films

Silicon nitride films were widely used in the semiconductor device industry as passivation layers,diffusion barriers,gate dielectrics and isolation material.Recently, hydrogenated amorphous silicon nitride(a-SiNx:H,SiN for short) as efficient antireflection coating(ARC) for silicon solar cells deposited by ECR-PECVD has attracted more attention. Compared to other antireflection(AR) materials like silicon dioxide,silicon nitride film has higher refractive index.It gives superior AR properties,particularly under encapsulation.The film also contains sufficient hydrogen which may diffuse into the mc-Si(microcrystalline silicon) or ribbon Si cells.These unique properties make SiN an ideal candidate for surface-passivating AR coating on solar cells.Generally,the traditional deposition technique of silicon nitride films is low-pressure chemical vapor deposition(LPCVD) or plasma enhanced chemical vapor deposition(PECVD). However,these processes may be incompatible with other fabrication steps because of the high processing temperature.As a high density plasma source,ECR systems have many advantages over conventional techniques.The consumption of precursors in the ECR-PECVD technique is very low,and the technique provides low ion-energy bombardment and low plasma damage.In addition,the technique allows the deposition of SiN films at low deposition temperatures with low intrinsic stress.In this work,the silicon nitride films have been deposited by Electron Cyclotron Resonance-plasma enhanced chemical vapor deposition(ECR-PECVD) technique,and the pure nitrogen is introduced into the ECR chamber as the plasma gas,the silane(Ar diluted, Ar:SiH₄=19:1) is used as precursor gas.We investigated the optimum deposition parameters of SiN films for photovoltaic application as an efficient AR coating.The actual composition of the films will be varied with the deposition conditions,such as gas flow rate ratio(N₂/SiH₄), substrate temperature,and microwave power.The effect of deposition parameters on the optical performance of SiN films was determined by Ellipsometry.The Si-N and N-H stretching characteristic peaks of SiN films have been observed by FTIR spectroscopy. Results shown that uniform silicon nitride films with low hydrogen content can be deposited at high deposition rate(10.7nm/min).The refractive index increased with the substrate temperature and microwave power increasing.The film shows good optical properties (refractive index is 2.0 or so) and satisfied surface quality(average roughness is 1.45nm) when the deposition parameter is 350℃and microwave power is 650W.