STRUCTURAL CHARACTERIZATION OF THE EPITAXIAL REALIGNMENT OF POLYCRYSTALLINE SILICON FILMS

The epitaxial realignment of polycrystalline silicon films deposited onto crystalline silicon substrates in the presence of a native oxide layer has been investigated during high temperature rapid thermal annealing. It is shown that the realignment mode of the polysilicon films is intimately related to the microstructure of the polysilicon layer during the heat treatment and to the morphology of the interfacial native oxide film. High resolution electron microscopy has been used to monitor the morphological changes the oxide film undergoes during heat treatments, and to characterize the structure of the boundary between realigned and non realigned regions. It is shown that the border regions are characterized by the {111} faceting typical of growth phenomena in silicon. The as-deposited, As doped films (with integer interfacial native oxide film) realign in a columnar mode, where the columns develop at sites where the oxide film has broken up into small beads. In films where the oxide film has been disrupted by a first high temperature preanneal before As doping, the thermal budget needed to complete their realignment is greatly reduced. In this case, due to the already disrupted oxide film and to the low thermal cycle used, the columnar structure does not develop and the layers realign by the motion of the whole interface towards the surface.