DENSITY OF AS-DEPOSITED AND ANNEALED THIN SILICON-NITRIDE FILMS

Density measurements of PECVD hydrogenated silicon nitride films, Si(x)N(y)H(z), are reponed. Two methods are investigated: the critical angle of reflection of x rays and direct calculations with atomic composition deduced from infrared chemical bond analysis. Two kinds of sample are studied: as-deposited films with different atomic compositions and films with given composition post-annealed up to 1000-degrees-C. On the first kind of sample both methods confirm the increase of density of the films when they are prepared in nitrogen-rich plasma. Moreover, from x-ray measurements, we deduce a maximum density of 3 +/- 0.1, dose to the high-temperature CVD silicon nitride value. In the second kind of sample, no significant change is observed in the specific mass, and this agrees with stability properties of the low-hydrogen-content almost stoichiometric silicon nitride reported recently.