Residual Stresses in Sputtered ZnO Films on (100) Si Substrates by XRD
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1201-H05-03
Residual Stresses in Sputtered ZnO Films on (100) Si Substrates by XRD
F. Conchon1, P.O. Renault1, P. Goudeau1, E. Le Bourhis1, E. Sondergard2, E. Barthel2, S. Grachev2, E. Gouardes3, V. Rondeau3, R. Gy3, R. Lazzari4, J. Jupille4, N. Brun5 1
Laboratoire de Physique des Matériaux (PHYMAT) UMR 6630 - Université de Poitiers, France Laboratoire de Surface du Verre et Interfaces (SVI), UMR 125, Aubervilliers, France 3 Laboratoire de Recherche de Saint-Gobain (SGR), Aubervilliers, France 4 Institut des Nanosciences de Paris (INSP), UMR 7588, Paris, France 5 Laboratoire de Physique des Solides (LPS), UMR 8502, Orsay, France 2
ABSTRACT Residual stresses in sputtered ZnO films on Si are investigated and discussed. By means of X-ray diffraction, we show that as-deposited ZnO films encapsulated or not by Si3N4 protective coatings are highly compressively stressed. Moreover, a transition of stress is observed as a function of the post-deposition annealing temperature. After a heat treatment at 800°C, ZnO films are tensily stressed while ZnO films encapsulated by Si3N4 are stress-free. With the aid of in-situ X-ray diffraction, we argue that this thermally-activated stress relaxation can be attributed to a variation of the chemical composition of the ZnO films. INTRODUCTION ZnO is one of the most interesting II-VI semiconductor with a wide direct band gap of 3.35 eV [1]. ZnO is an optically transparent material of technological importance for its practical and potential applications for short wavelength optoelectronic devices and transparent conductive oxide films, such as blue to UV light-emitting diodes or solar cells electrodes [2]. Various deposition techniques have been applied for ZnO films elaboration such as rf and dc magnetron sputtering [3], metal-organic chemical vapor deposition (MOCVD) [4], pulsed laser deposition (PLD) [5], or filtered cathodic vacuum arc technique [6]. The advantage of the magnetron sputtering technique is the achievement of polycrystalline ZnO films deposition on large area without intentional substrate heating. However, it results in residual stresses which can be detrimental when occurrence of spontaneous delamination, or under scratch during processing or in service. Of the many articles about the preparation of zinc oxide films, only a handful report about stresses in these films whereas many studies have been carried out on the electronic and optical properties of the ZnO bulk, films, and nanostructures [7,8,9,10,11,12]. Stresses being correlated to thin films physical properties, their control hence requires an in depth comprehension of stresses formation and relaxation mechanisms. In the present study, we propose with the aid of X-ray diffraction (XRD) to study residual stresses in sputtered ZnO films deposited on Si. In particular, we will evidence a thermally-induced stress relaxation observed by in-situ XRD, the origin of which can be attributed to the presence of point defects in the ZnO films.
EXPERIMENTS ZnO films (100 nm thick) were deposited by magnetron sputterin
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