HIGH-RESOLUTION DEPTH PROFILING OF ULTRATHIN SILICON-OXIDE NITRIDE OXIDE LAYERS

We demonstrate that in situ ellipsometry in conjunction with reactive ion etching is capable of providing high-resolution (less-than-or-equa l-to 0.3 nm) compositional depth profiles of thin (congruent-to 5 nm) silicon oxide/nitride/oxide (ONO) structures, which are superior to th ose which can be obtained by other methods. A low presure (75 mTorr), low power (50 W) CF4 plasma was employed to etch slowly the ONO multil ayer structure with Si3N4/SiO2 etch rate ratio of approximately 4. The instantaneous etch rate as a function of depth was measured by automa ted ellipsometry, providing a measure of the composition.