Thin Solid Films 278 ( 1996) 12-17 Depth profiling of thin IT0 films by grazing incidence X-ray diffraction D.G. Neerinck ‘, T.J. Vink * Philips Research Laboratories, Pro$ Holstlaan 4, 5656AA Eindhoven, The Netherlands Received 18 April 1995; accepted 14 September 1995 Abstract Tin-doped In20, (ITO) films, deposited at room temperature by dc. magnetron sputtering, display a double-layer structure after post- deposition annealing. The films consist of a stress-free polycrystalline bottom layer and a severely stressed polycrystalline top layer. Standard 20-19X-ray diffraction reveals doublet-type peak profiles. Asymmetric Bragg X-ray diffraction with a grazing angle of incidence was used to assess the stress-depth relation. Measuring diffraction peak positions of the doublet peak profiles and correcting for refraction has enabled us to determine Young’s modulus E and Poisson’s ratio v for ITO. The thicknesses of the two constituent layers of the IT0 film can be determined by measuring the integrated peak intensities as a function of incidence angle and correcting for texture. The X-ray diffraction results were compared with a single cross-sectional transmission electron microscopy analysis. Keywords: Depth profiling; Elastic properties; Indium oxide; Tin oxide; X-ray diffraction 1. Introduction Tin-doped In,O, (ITO) films are widely used in optoelec- tronic applications such as liquid crystal displays because of their relatively low resistivity and high transmissivity to vis- ible light [ 11. Additional requirements for applicability of IT0 as a transparent conductor in displays are good etcha- bility to enable device patterning and low internal stress to prevent deformation. These functional properties are highly dependent on the microstructure of the films resulting from specific deposition and processing conditions. In a previous study, it was shown that the 0, partial pressure during sput- tering, the deposition temperature and post-deposition annealing have a pronounced influence on the film’s struc- tural properties, in particular on the homogeneity in the direc- tion normal to the sample surface [ 21. For instance, sputter deposition of 1 200 A thick films at room temperature in an oxygen-deficient ambient resulted in an amorphous IT0 layer, whereas at elevated O2 partial pressures the films were almost completely polycrystalline. Typically, at intermediate O2 partial pressures (15 mPa) both phases coexisted, an amorphous sublayer present near the substrate and a poly- crystalline layer on top of it. The polycrystalline top layer was found to exhibit in-plane compressive stress. Annealing * Corresponding author. ’ Present address: Bekaert N.V. Bekaertstraat 2, B-8550 Zwevegem, Belgium. 0040-6090/96/$15.00 0 1996 Elsevier Science S.A. All rights reserved SSD10040-6090(95)08117-8 this film at 520 K for 1 h in vacuum resulted in crystallisation of the bottom layer while leaving the stress in the top layer unaffected. The annealed IT0 films, deposited at an inter- mediate O2 partial pressure of 15 mPa, thus display a double- layer structure consisting of a polycrystalline stress-free bottom layer and a polycrystalline stressed top layer. Further discussion on the enhanced crystallization with increasing 0, partial pressure and the occurrence of stress-depth gradients in the films is given in Ref. [ 21 and references cited therein. In order to assess the stress-depth dependence and to deter- mine the thickness of both layers of the IT0 film, grazing incidence asymmetric Bragg X-ray diffraction (GIABXD) was applied. Lim et al. demonstrated the use of a small angle of incidence to reduce the X-ray penetration depth in com- bination with parallel beam optics enabling surface-sensitive X-ray diffraction [3]. Toney et al. applied GIABXD to perform structural depth profiling of thin Fe,O, films [4], while Takayama and Matsumoto performed a detailed study of diffraction peak positions and diffracted intensities of Au/ Cu and CulAu bilayers as a function of the angle of incidence [5]. In this paper, an IT0 thin film displaying the double- layer structure as described above is analysed using GIABXD. The penetration depth is controlled by varying the incidence angle over more than 10”. Peak positions and inten- sities are analysed taking refraction, absorption, texture and surface enhancement of the incident X-ray energy at grazing angles into account.