Texture studies of Si1-xGex thin films by x-ray diffraction and transmission electron microscopy

X-ray diffraction (XRD), transmission electron microscopy (TEM), and transm ission electron diffraction (TED) were used to measure the texture of undop ed poly-Si1-xGex thin films with x = 0, 0.018, 0.13, and 0.31. The films we re grown by chemical vapor deposition onto oxidized Si wafers covered with a thin poly-Si seed layer, which was deposited using SiH4 to assist nucleat ion. SiH2Cl2 was used to deposit the poly-Si reference sample, and SiH2Cl2 mixed with GeH4 was used for Si1-2Gex. To span a wide range of Ge content, the deposition temperature was lowered hom 800 degreesC (x=0) to 600 degree sC (x=0.31) as the Ge fraction increased. All films, independent of Ge cont ent (0 less than or equal tox less than or equal to0.31), showed similar XR D spectra. The spectra exhibited a strong {110} fiber texture, with the int ensity for differently oriented grains decreasing in the sequence {110}, {3 11}, and {111} for all films, even though grains in the seed layer appeared to be randomly oriented. Wedge-shaped specimens analyzed by TED showed tha t (110) texture was already present at the bottom (film/seed-layer interfac e) of all the films investigated and increased toward the top (film/air int erface). Cross-section TEM images showed that all films exhibited a columna r structure and contained numerous V-shaped grains. Plan-view TEM showed th e presence of numerous microtwins in all films. The results suggest that, u nder our experimental conditions, similar mechanisms dominate the developme nt of texture in Si1-xGex and in poly-Si. (C) 2001 American Vacuum Society.