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 (≤0.3 nm) compositional depth profiles of thin (≃5 nm) silicon oxide/nitride/oxide (ONO) structures, which are superior to those 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 multilayer structure with Si3N4/SiO2 etch rate ratio of ~4. The instantaneous etch rate as a function of depth was measured by automated ellipsometry, providing a measure of the composition. © 1993, The Electrochemical Society, Inc. All rights reserved.