Study of nitrogen doped silicon films used for p+ polysilicon gates

The effects of thermal annealing conditions, and nitrogen tenor on the properties of nitrogen doped silicon films (NIDOS) deposited by low-pressure chemical vapor deposition (LPCVD) at low temperature (480°C) from a mixture of disilane and ammonia are investigated. Two series of samples have been studied: boron doped NIDOS films and NIDOS films. The resistivity measurements and the scanning electron microscopy observations showed respectively, a conducting behavior and a polycrystalline structure of films at high temperature. The electrical characterization highlighted the improvement of NIDOS conductivity when the nitrogen content increases. Fourier transform spectrometry measurements revealed that nitrogen combines with the boron to form a B-N complex for boron doped NIDOS films. This complex is responsible of the increase of the resistivity values of boron doped NIDOS films when the nitrogen tenor increases. Results showed a good correlation between the electrical and the structural properties.