| Metal Induced Crystallization(Metal Induced Crystallization:MIC)is a very promising method to grow high-quality polysilicon on glass substrates.Of the current studies of the metal-induced crystallization,aluminum attracted great attention because it introduced the shallowest level into silicon band,closest to the valence band,and can be used as a P-type doping impurity.So aluminum is more conducive inducing metal to obtain better electrical properties for the polycrystalline materials.In this work,(111)oriented growth of polycrystalline silicon was achieved by the aluminum induced crystallization(AIC).The experimental investigations were focused on the effect of the thickness of the Al layer?annealing temperature?thicknesses of both the SiO2 layer and Al2O3 layer on the surface.Based on the polycrystalline silicon which was used as a seed layer,epitaxial growth was carried out by the PECVD(Plasma Enhanced Chemical Vapor Deposition).The structure and crystalline quality of the poly-crystalline material formed by the AIC were characterized by confocal microscopy?Raman spectroscopy?XRD?SEM?AFM and other testing methods.The thesis mainly includes two parts,(1)growth of the(111)orientated Si layer by the metal induced crystallization,and(2)optimization of the epitaxial layer.The main work and achievements are as follows:(1)It was found that,by sputtering different thickness of A1 layer,the thicker the Al layer is,the more the residual Al is on the surface.The 80nm thickness of the Al layer was the critical value,and highly oriented Si(111)films were induced with the thickness of Si(200nm)/Al(80nm).(2)The growth of the Si by Al induced crystallization was studied by setting the Si(200nm)/SiO2(8nm)/Al(80nm)with being annealed at 450? for 3 hours,8 hours,500 ? 8 hours,respectively.It was confirmed by the experiments that an amorphous silicon crystallization occurred when annealing at 450?,whilst high-quality oriented growth Si(111)film were achieved when annealed at 500? with an increased crystallization speed.(3)A silicon dioxide layer was made as embedded layer using the RF-magnetron sputtering(Radio Frequency magnetron sputtering).With 4nm,8nm and 16nm thick silicon dioxide layers being deposited respectively,laminated films were annealed at 500? for 8 hours under a nitrogen atmosphere.The results showed that highly orientation Si(111)was achieved for all of the three samples without other crystalline phases.The existence of the interfacial layer of SiO2 inhibited the direct reaction of Si and Al to create alumina-silica,reducing the diffusion rate of Si and promoting(111)direction oriented growth.(4)It was found that a denser film with little void density was obtained in a naturally oxidized sample,compared to those samples without naturally oxidization.The same efficiency was achieved by sputtering a Al2O3 layer on the aluminum surface,XRD results indicated that the sample with the Al2O3 layer had the stronger Si(111)peak intensity compared with the sample without the Al2O3 layer.The presence of Al2O3 layer improved the wet ability of the induced polycrystalline Si on Al surface,promoted Si lateral growth and formed a dense film in the surface.(5)The epitaxial growth was tested by using PEVCD to deposit Si layer on the obtained(111)oriented Si film.The deposited Si thin film was amorphous by annealing at 500 ?for 8 hours.However(111)orientation polycrystalline silicon layer was obtained after rapid thermal annealing at 1000?.The phenomenon indicated that the annealing at 500? did not induce the amorphous silicon to transform to Si(111),whilst the annealing at 1000?resulted in the transition.This method can be used to grow thick poly-silicon thin films,finding wide applications in solar cells. |
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