SIMS STUDY OF RAPID THERMAL NITRIDATION OF SILICON DIOXIDE THICK-FILMS IN AMMONIA AMBIENT

Thick silicon dioxide layers (1.5 mum) have been nitrided in a lamp-he ated furnace in an ammonia ambient. Temperatures of 700-1100-degrees-C were used for the nitridation for times of 5 to 300 s at atmospheric pressure. The distribution of the nitrogen in the nitrided samples was obtained using SIMS. The exponential shapes of the nitrogen profiles have been interpreted by a mechanism involving diffusion of the nitrid ing groups (NH3) with a reaction with the network. We obtained the val ues of the effective diffusivity D = D(NH3) C0/N(i) and of the reacti vity k = k(cn)C0/N(i) correlated by the length of exchange x0 = (D*/k )1/2. It appears that the increase of k* with the temperature is larg er than the increase of D. This finding implies a shorter length of e xchange at high temperature than at low temperature.