Study On Crystallization Properties Of Polycrystalline Si Thin Films Deposited By Ge - Buried Layer

With advantages of high mobility and illumination stability like monocrystallinesilicon and large area fabricating and low cost like amorphous silicon thin film,Polycrystalline silicon thin film has a wide application prospect in thin film solar cells,thin film transistors (TFT) and microelectronics integrated circuit(MIC). So, the basicresearch on polycrystalline silicon thin film and application have always been a hotresearch topic in photovoltaic science and the field of photoelectric information,despite the silicon prices continuing to fall in recent years. Among many preparationmethods of polysilicon thin film, the metal-induced crystallization possesses theadvantages of short crystallization time, low crystallization temperature and big grainsize. But in the polysilicon thin film by this method, metal atoms as induced sourcealso cause certain pollution to it, which drops the performance of it and narrows itsapplication scope.In this paper, by optimizing the inducing metal resource, we chose Ge as inducemetal resource. Ge has similar physical and chemical properties with Si, thus Gereplacing metal as induction source can reduce pollution. In this paper, using theelectron beam evaporation amorphous Si thin films with Ge buried layer on singlesilicon substrates are preparated. And these amorphous Si thin films are annealed atdifferent temperature in vacuum. The structures of the above thin films arecharacterized by Raman spectrum, X-ray diffraction (XRD), atomic force microscope(AFM), field emission scanning electron microscopy (FESM) et al.The contributionof substrate temperature and subsequent annealing to Ge-induction amorphous Si thinfilm crystallization is studied. And Ge-induced crystallization mechanism is firstlyexplored. The main conclusions are as follows:(1) The samples grown at ambient temperature contained a buried Ge layer of250nm were crystallized with a preferential orientation of Si (111) at the annealingtemperature of400℃for5hours. For the sample annealed at temperature of600℃possessed a high orientation of Si (111), and the corresponding grains size reaches20μm.(2) As increasing substrate temperature to300℃, Si thin films grown on Sisubstrate with the same buried Ge layer were still amorphous silicon after annealing at temperature of700℃for5hours.(3) The a-Si thin film without Ge buried layer can be crystallized when annealingtemperature is800℃for the same annealing time; crystallization rate is46%;(4) Under the same preparing conditions, we prepared two different structure filmsof Ge sandwich (a-Si/Ge/a-Si/Sisubstrate) and Ge cap layer (Ge/a-Si/Sisubstrate),keeping them annealing temperature of700℃for5hour, the films did not crystallize.(5) DSC scanning analysis showed that the crystallization of thin film grown atambient temperature and followed by annealing is a result of stress-release induction.The stress release acted as dominant factor for the crystallization of a-Si film whenannealed temperature approaching a threshold of around400℃；(6) When Ge induces a-Si crystallization, the films had peeling phenomenon, whichis because of lattice mismatch between the epitaxial films and the substrate in theprocess of annealing.