The role of metal impurities (Cr and Ni) in the crystallization of a-Si thin films has been studied using x-ray absorption fine structure spectroscopy (XAFS). The growth process involves two geometries (1) the deposition of 50 nm Cr/Ni films on fused silica substrates followed by deposition of 400 nm amorphous Si (a-Si) films at different substrate temperatures and (2) 400 nm a-Si deposition followed by 50 nm Cr/Ni deposition. X-ray Absorption studies were carried out using the BM08 GILDA Beamline of the European Synchrotron Research Facility (ESRF, Grenoble, F) in fluorescence mode. To understand the evolution of the local structure of Cr/Ni diffusing from bottom to top and from top to bottom, in metal on top and metal bottom geometries respectively, total reflection (to study top layers) and higher incidence angles (to study bottom layers) were employed. The resulting metal environment is quite complex: we applied independent XANES and EXAFS analysis to validate a method of quantifying the relative content of metal, metal oxide and metal silicides compounds in the different films. Significant differences have been found when comparing Cr- and Ni-doped films, due to the different diffusivity of metals and to the strong influence of deposition and annealing temperature. In general, from this work, we conclude that metal diffuses into the a-Si matrix and reacts with it at sufficiently high temperature to form metal silicides, in particular (Cr/Ni)Si2. Later these silicate nuclei will act as crystallizing seeds for the a-Si crystallization.
"Metal induced crystallization of amorphous silicon thin films studied by X-ray absorption fine structure"
F Rocca
2012
Abstract
The role of metal impurities (Cr and Ni) in the crystallization of a-Si thin films has been studied using x-ray absorption fine structure spectroscopy (XAFS). The growth process involves two geometries (1) the deposition of 50 nm Cr/Ni films on fused silica substrates followed by deposition of 400 nm amorphous Si (a-Si) films at different substrate temperatures and (2) 400 nm a-Si deposition followed by 50 nm Cr/Ni deposition. X-ray Absorption studies were carried out using the BM08 GILDA Beamline of the European Synchrotron Research Facility (ESRF, Grenoble, F) in fluorescence mode. To understand the evolution of the local structure of Cr/Ni diffusing from bottom to top and from top to bottom, in metal on top and metal bottom geometries respectively, total reflection (to study top layers) and higher incidence angles (to study bottom layers) were employed. The resulting metal environment is quite complex: we applied independent XANES and EXAFS analysis to validate a method of quantifying the relative content of metal, metal oxide and metal silicides compounds in the different films. Significant differences have been found when comparing Cr- and Ni-doped films, due to the different diffusivity of metals and to the strong influence of deposition and annealing temperature. In general, from this work, we conclude that metal diffuses into the a-Si matrix and reacts with it at sufficiently high temperature to form metal silicides, in particular (Cr/Ni)Si2. Later these silicate nuclei will act as crystallizing seeds for the a-Si crystallization.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
