Spectroscopic investigation of the synthesis of thin silicon nitride filmson silicon single-crystal wafers via ammonia-assisted pyrolysis of organosilicon polymers

Thin layers of a-Si3N4 were synthesized by the pyrolysis of thin films of p oly(methylsilane) (PMS) and poly(dimethylsilane) (PDMS) spin-coated on sili con single-crystal wafers and via deposition of the volatile species result ing from the thermal cracking of the bulk precursor in the presence of ammo nia. The process was monitored by FT-IR spectroscopy. The reaction between NH3 and PMS begins at 200 degreesC with the slow production of a slightly c ross-linked product involving Si3N knots. Extensive amination of PMS occurs on pyrolysis at 300 degreesC, under 5-10 Torr NH3 overpressure. The produc t exhibits IF bands characteristic of both a silazane and an aminosilane sp ecies, which are presumably formed by Si-H and N-H heterodehydrocoupling. B etween 200 and 450 degreesC, this cross dehydrocoupling reaction competes v ery effectively with the Kumada rearrangement. Significant loss of carbon o ccurs from the resulting poly(carbosilazane) between 500 and 600 degreesC. Prolonged curing under NH3 at 300 degreesC, to remove all Si-H groups and t o give a densely cross-linked polysilazane, suppresses the Kumada rearrange ment, and negligible carbon loss occurs on raising the pyrolysis temperatur e to 700 degreesC. Although the main product is still a-SI3N4, there is an increased amount of residual carbon.