A polycrystalline silicon film 0.55 μm thick was deposited in a low-pressure CVD reactor on a Si3N4 substrate. Islands of various sizes (2×20 μm up to 20×160 μm) were prepared by standard photolithographic techniques. Laser annealing was then performed under conditions which are known to cause an increase in grain size from ∼500 Å to long narrow crystals of 2×25 μm in a continuous polysilicon film. These same conditions were found to produce single-crystal 〈100〉 material in the (2×20 μm) islands. However, 25×25-μm and 20×160-μm islands remain polycrystalline after the laser scan.

The resistivity reduction in heavily doped polycrystalline Si by laser annealing and its increase during subsequent heat processing have been studied. Both cw and pulsed lasers have been used for the experiments and the results are compared. In both cases laser annealing reduces the Si resistivity by a factor of 2–3 compared to the furnace annealing. A limited resistivity increase is observed in all laser-annealed Si samples during subsequent thermal annealing, with the final values for resistivity being lowest for cw-laser-annealed Si. The subsequent annealing behavior observed for cw- and pulsed-laser-annealed Si is interpreted in terms of the different grain structures found in these films. It is demonstrated by transmission electron microscope studies that the resistivity instability is caused by the precipitation of dopants in the form of rod shaped structures localized at the grain boundaries as well as within the crystallites.