The effects of thermal treatment on the anisotropic etching behavior of Cz- and Fz-silicon

We investigated the effects of stepwise thermal treatment of [100]-CZ- and FZ-silicon on the crystal defects and the etching behavior in KOH solutions . The anisotropy (the quotient of the vertical etch rate and the underetchi ng of the mask), formed crystal defects as well as the surface roughness of the exposed {100}- and {111}-planes are examined. Thermal treatment of the silicon substrate can result in a precipitation of the interstitial oxygen. The precipitated oxygen causes elastic stress in the crystal which can be relieved by a generation of defects [1,2]. We foun d out that the evolution of these defects accelerates the lateral etch rate considerably. For the reference, the samples without thermal treatment the anisotropy has a value of 120 for FZ-silicon and 70 for CZ-silicon, respec tively. However, with rising temperature and process time the anisotropy de creases to 30 for FZ-silicon and 15 for CZ-silicon. At the same time, the s urface quality of the {100}- and {111}-planes degrades with increasing temp erature. The roughness value Ra rises from 5 nm to approximately 30 nm. Alo ng with the variation of the etching behavior during thermal treatment, we further present a suitable model for the oxygen-dependence of the etch rate . (C) 2000 Elsevier Science B.V. All rights reserved.