EFFECT OF DOPANTS ON GRAIN BOUNDARY MOBILITY IN SILICON.

In sufficiently thin films of silicon ( APP 1STH 1200 Angstrom), secondary or abnormal grain growth leads to bimodal grain size distributions and eventually to grain sizes much greater than ( APP GRTH 50x) the film thickness. The resulting grains have non-random texture and are thought to be the result of surface-energy-driven secondary grain growth. The rate of normal and secondary grain growth greatly increases with increasing phosphorus or arsenic content (P and As are donors). The rate of normal grain growth is unaffected (or increases slightly) with increasing boron content (B is an accepter). The rate enhancement caused by P and As is thought to be caused by increases in the grain boundary mobility. Above 1000 degree C, the grain boundary mobility enhancement caused by P doping can be compensated (reduced or eliminated) by B doping. These results are discussed in the context of theoretical models for secondary grain growth and grain boundary motion in thin semiconductor films.