Evolution of Special Grain Boundaries and Relative Grain-Boundary Energy in Phosphorus-Doped Polysilicon Films under Annealing

The effect of annealing on the grain-boundary structure and the relative grain-boundary energy of phosphorus-doped polysilicon films, obtained by low-pressure chemical vapor deposition, was studied by transmission electron microscopy and atomic force microscopy. The obtained distributions of the types of grain boundaries for different annealing temperatures showed that a significant part of the grain boundaries in polysilicon films are special grain boundaries, in particular, twin boundaries of different orders of twinning. It is assumed that the difference in the distributions of special boundaries for different annealing temperatures is due to the difference in the mechanisms of grain growth in different temperature ranges. The relative amount of a particular type of special grain boundaries in the films is determined by the annealing temperature and is the result of processes that take place when the temperature increases, in particular, the processes of growth of first-order annealing twins and splitting of high-order twin boundaries. Estimates of the relative grain-boundary energy by the method of grain-boundary grooves based on the data of atomic force microscopy, have shown that the relative grain-boundary energy decreases with an increasing of annealing temperature. Such a decrease is due to an increase in the number of special boundaries, faceting of grain boundaries.