ANNEALING OF SILICON-NITRIDE THIN-FILMS PREPARED BY PLASMA-ENHANCED CHEMICAL VAPOR-DEPOSITION WITH HELIUM DILUTION

Silicon nitride thin films were prepared by plasma-enhanced chemical vapor deposition with nitrogen, ammonia, silane and helium gas mixtures. Increasing the [N2]/[NH3 + N2] ratio from 0. 75 to 1 resulted in a decrease in the hydrogen content in the films down to 8%. These films were annealed up to 1000-degrees-C. Using IR spectroscopy measurements we studied the evolution of the chemical bonds, while the evolved hydrogen was measured upon thermal effusion in an ultrahigh vacuum cell by a mass spectrometer. We discuss the thermal stability of these films and we show that internal chemical reordering is favored with regard to the effusion of hydrogen. This effect is larger in low hydrogen content than in high hydrogen content silicon nitride.