The Research Of Radio Frequency Plasma CVD In Preparing A-Si:H Thin Film

As a kind of commonly used optical thin film material,silicon thin film has lots of advantage,its process is simple and can be prepared in a variety of substrates and compatible with silicon semiconductor technology and low production costs.These good performance of amorphous silicon thin film make it widely used in solar cells.The purpose of this paper is using two different kinds of PECVD,the capacitance coupling plasma enhanced chemical vapor deposition method?CCP-CVD?and inductively coupled plasma enhanced chemical vapor deposition method?ICP-CVD?,using SiH₄ and H₂ gas to prepare a-Si:H thin film with a variety of parameters.We compared the principle and characteristics of these two kinds of PECVD.And by adjusting the SiH₄/H₂gas flow ratio,power,pressure and substrate temperature,we prepared a number of Si thin film.We also studied the cleaning process condition of CCP-CVD to ensure the process stability.And we also studied the influence of these parameters on thin film deposition rate,uniformity,surface morphology and optical properties etc.The main results are as follows:SiH₄ and H₂ flow has great influenced on glow discharge of CCP-CVD equipment.With the increase of SiH₄ gas flow,glow color changes from dark purple to blue to dark purple.When SiH₄ gas flow is 15sccm,H₂ gas flow is 10 sccm,the glow is the most stable.Power and pressure has little effect on glow stability.As the process time increase,glow color became dark and inside the cavity deposited amorphous silicon particle.SF₆ and O₂ gas can be used to etch amorphous silicon particles.When SF₆ gas flow is 15 sccm,O₂ gas flow is 5 sccm,the etching rate is the fastest and etching effect is the best.For polycrystalline silicon thin films,we observed that 98%of hydrogen dilution ratio with a SiH₄ flow rate of 2 sccm and H₂ flow rate of 98 sccm is suitable.Furthermore,higher power of 3 kW and higher temperature of 400?and 10 mTorr process pressure increased the crystalline volume fraction Xc of poly-Si films.The highest conductivity of n-type poly-Si thin film which was obtained with the doping gas PH₃ diluted in 99%H₂,was1.916?^-1?cm^-1.Hydrogenated amorphous silicon films were fabricated by tuning the process parameters to lower power of 1.5 kW,lower temperature of 200?,and lower hydrogen dilution of 77%.In the case of p-type amorphous silicon thin films,the conductivity obtained was 0.315?^-1?cm^-1.For the highest band gap of 1.705 eV with the doping gas B₂H₆ diluted in 99.5%H₂.