Polycrystalline silicon thin films formed by metal-induced solid phase crystallization of amorphous silicon

Metal-induced solid phase crystallization (MISPC) was performed on plasma-enhanced chemical vapor deposited a-Si:H films which were deposited at substrate temperatures between 100 and 320 °C on bare or SiN_x-coated Corning code 7059 glass substrates. The nickel or palladium layers used in the MISPC were thermally evaporated on the a-Si:H film surfaces to thicknesses of 5, 10, or 15 Å. We then examined the MISPC kinetics and its dependence on the precursor a-Si:H deposition temperature, the substrate coating, and the metal layer thickness. For the metals used in this study, it is found that the crystallization time and the microstructure and size of grains in the MISPC polycrystallization silicon (poly-Si) films are independent of the precursor a-Si:H deposition temperature, the metal layer thickness, and the substrate coating; however they are dependent on the metal type. It is argued that the formation of suicides and the solubility of metal in silicon, during the annealing, play important roles in enhancing crystallization. It is also found out that the diffusion of metal impurities into silicon from the metal layer used in the MISPC is detrimental to the electrical properties of the forming poly-Si and to the characteristics of thin film transistors fabricated in the poly-Si.