Thermal stability of undoped polycrystalline silicon layers on antimony and boron-doped substrates

摘要

The structure of as-deposited and annealed polycrystalline silicon layers has been investigated by scanning electron microscopy and x-ray diffraction. The structure of intentionally undoped layers prepared by low pressure chemical vapor deposition at a temperature of 640 ℃ was found to be stable upon annealing at temperatures lower than about 900 ℃. On the other hand, primary recrystallization of the layers has been observed during annealing at temperatures in the range of 900 to 1150 ℃. Isochronal annealing revealed the activation energy for the primary recrystallization of undoped layers as 0.6 eV. The activation energy for diffusion of silicon self-interstitials along the grain boundaries was calculated to be 2.2 eV. The difference in grain-growth process was observed for the undoped layers grown either (ⅰ) on lightly boron-doped substrate or (ⅱ) on the substrate heavily doped with antimony. The different grain-growth mechanism was found to be a consequence of antimony diffusion into the polycrystalline layer.