Effect of nitrogen on the diffusion and the activation of the boron implanted in polysilicon thin layers

This work deals with the study of polysilicon thin layers doped in-situ with nitrogen, know as nitrogen doped silicon (NIDOS), strongly doped boron. These films are used in microelectronics technology as P+ MOS transistors gates, etc. The study of nitrogen effect on the redistribution and the activation of boron during annealing in NIDOS film is necessary. These films were deposited by low pressure chemical vapor deposition using a mixture of disilane and of ammonia, with a nitrogen content, varying from 0 to 16%. The study of secondary ion mass spectrometry (SIMS) profiles showed that the boron diffusion is reduced with increasing nitrogen ratio. The resistivity of films increases with increasing nitrogen ratio. The surface roughness measurement illustrates that the initially amorphous films present a smooth surface, but after annealing the roughness is about some nanometers. Finally, scanning electron microscope (SEM) observations showed a significant crystallization of the films without nitrogen, annealed at 850°C/15 min. Whereas, films with weak nitrogen content, annealed at 1050°C/15 min showed a start of crystallization. We can note that the obtained results by various characterizations are in good agreement for the reduction of the boron diffusion and the crystallization of deposits during thermal annealing.