Characterization of Arsenic-Implanted Amorphous Silicon

ABSTRACTIn this study, amorphous silicon and polycrystalline silicon films were implanted with arsenic and subjected to varied low temperature (<900°C) anneal conditions and characterized using TEM. The microstructure is of interest for later correlation with electrical measurements. The amorphous deposition produces larger, more irregular grains with more strain than does the polysilicon deposition for a single-step rapid thermal anneal (RTA) cycle. This can be explained by the number of critical nucleii and the rate of grain growth. The sheet resistivity, as measured by four-point probe, correlates to the deposition conditions. A two-stage anneal makes the grains less irregular by reducing the roughness of the grains and decreasing the strain in the grains. For a given deposition condition, the final microstructure is most strongly influenced by the first anneal. The second anneal produces no clear change in grain size. 800°C anneals result in larger grains than 900°C anneals. This is explained by the presence of less critical nucleii for 800°C anneals. In comparing short and long durations of RTA, the short duration produced slightly larger grains than the long duration RTA due to greater nucleation in the longer RTA wafers. In the case of RTA versus furnace anneals, RTA produces larger, more irregular grains, with more strain in the grains. A model in terms of the size of critical nucleii is used to explain the difference.