CHARACTERIZATION OF NITRIDED SIO2 THIN-FILMS USING SECONDARY-ION MASS-SPECTROMETRY

For the fabrication of MOS devices, the incorporation of nitrogen into thin SiO2 dielectric films has been shown to improve the electrical a nd structural integrity of the films. For example, nitrogen present at the SiO2/Si interface acts to enhance the charge-trapping properties of the oxide. Furthermore, nitrided oxides are more resistant to impur ity and dopant diffusion and further oxidation than non-nitrided films . The understanding of the nitriding process has progressed to the poi nt where the distribution and concentration of the nitrogen (the N dep th profile) can be controlled, to some extent. The final N depth profi le in these films is a critical piece of information to the process en gineer. By using different nitriding agents and growing the films usin g varying temperatures and times, the nitrogen can be 'concentrated' a t virtually any depth in a very thin oxide (< 100 Angstrom). We have s uccessfully employed secondary ion mass spectrometry (SIMS) for determ ining the nitrogen distributions in such films. Using an SiO2 standard , calibrated both in terms of concentration and film thickness, accura te quantification of unknown samples has become straightforward. Throu gh the extensive development of the instrumental protocol, the long-te rm reproducibility of this measurement has been shown to be better tha n 9%. The N detection limit using this protocol is approximately 0.001 % atomic. We will present recent examples of results using SIMS on die lectric films processed using a variety of oxidation and nitridation c onditions.