Strain investigation of low strained buried gratings by grazing incidence X-ray diffraction and elasticity theory

¹ Fraunhofer-Institut für Zerstörungsfreie Prüfverfahren - Krügerstrasse 22 D-01326 Dresden, Germany
² Institut für Festkörperphysik, Universität Potsdam - D-14469 Potsdam, Germany
³ France Télécom, CNET/DTD - BP 107, F-92225 Bagneux Cedex, France

Received: 27 April 1998
Accepted: 9 March 1999

Abstract

We investigate the strain evolution in low strained gratings before and after embedding in the substrate material by high-resolution grazing incidence X-ray diffraction and elasticity theory. For the experiments, we use a non-coplanar multiple crystal arrangement. A suitable selection of reflections allows us to characterise the grating shape independently of the strain state. Depth selective measurements give evidence for a non-uniform strain relaxation in the surface grating and a complete planarization of the sample surface by the burying process. In the buried grating a counteraction of the embedding material is found. The counteraction only leads to a partial restraining of the grating. There remains a laterally periodic strain modulation in the grating, which extends into the non-patterned material below and above the grating and reaches the free surface of the embedding material. The experimental findings are confirmed by calculations of the strain field based on elasticity theory. The subsequent simulations of the diffraction patterns show a good quantitative agreement with experiment.