Aluminum-induced Preparation Of Polycrystalline Silicon Thin Film Crystallization

In this thesis,we have studied the fabricating polycrystalline-silicon(poly-Si) thin films by aluminum-induced crystallization of amorphous silicon(a-Si) thin films on glass substrate.Some influential factors on the crystallization of a-Si thin films,which include annealing condition, thickness of Aluminum thin film,fabrication condition of aluminum thin film,and so on,are studied. The structure properties of the fabricated poly-Si thin films have been investigated by X-ray diffraction(XRD),Raman spectrum and Atomic Force Microscopy(AFM).The following conclusions have been achieved:1.Annealing temperature has an important influence on the crystalline of a-Si thin films.Although it is reported that aluminum-induced crystallization of a-Si thin films can take place at a temperature as low as 150℃,preparation of high-quality poly-si thin films must be appropriately raise the temperature,at least more than 300℃.At high temperature,for example at 500℃,samples crystallized rapidly,and extension of the annealing time did not significantly affect results of crystallization.2.After the a-Si transformed into the ploy-Si,preferred orientation of Si(111) appeared.The longer annealing time and higher annealing temperature,the preferred orientation is more obvious.3.Under the same conditions,both the crystalline volume fraction and size of crystalline grain increase with annealing time increasing,the diameter of the biggest grain achieved is 156nm. However,the roughness of the samples is also increased.4.Under the same conditions,for the higher annealing temperature,the crystallization of the samples is faster.For a greater nuclear density and smaller grains,the surface of the poly-Si thin film is smoother.5.There is an optimal thickness ratio for the aluminum film to the a-Si film.When the ratio is 1:1, the crystallization is the best.6.The surface of the aluminum film oxidized into alumina by air prior to a-Si:H film deposition. Alumina layer has an important influence on the crystallization of a-Si:H film.If the thicker alumina layer,the harder diffusion of aluminum atoms and silicon atoms,the smaller concentration of aluminum in a-Si:H film and of silicon in aluminum film,so it makes nucleation density of silicon smaller,that leads to the large-grained silicon growth.Otherwise,the thinner alumina is,the higher nucleation density of silicon,which results in the small-grained silicon.