Influence of deposition parameters on the stress of magnetron sputter-deposited AlN thin films on Si(100) substrates
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In this work, a systematic study of the influence of five deposition parameters, i.e., process pressure, substrate temperature, target power, and substrate bias, as well as gas composition on the residual stress in fully textured polycrystalline aluminum nitride thin films deposited on Si(100) wafers using the reactive sputtering method was performed. Post-growth residual stress measurements were obtained indirectly from radius of curvature measurements of the wafer prior to and after deposition. Two different techniques were used to determine the curvature: an optically levered laser beam and an x-ray diffraction method. Stresses in both cases were then evaluated using the Stoney formulation [G.G. Stoney, Proc. R. Soc. (London) A82, 172 (1909)]. Both methods give similar results, with slight quantitative differences. The existence of a transition region between tensile and compressive stress previously reported in the literature is also confirmed. The transition is shown to be strongly dependent on the process parameters. Optimal films regarding stress were grown at 2 mtorr, 900 W at the target, a 20/45 Ar/N2 gas mixture, and floating potential at the substrate. The substrate temperature did not influence the measured internal stress in the films.
I. INTRODUCTION
The aim of this work was to study stress evolution during reactive sputter deposition of fully textured caxis-oriented polycrystalline AlN thin films as a function of the main process parameters and to find optimal conditions for the synthesis of low stress AlN thin films grown on Si-100 substrates. Although not studied here, it should be pointed out that Meng1 reported how AlN films deposited on both Si-100 and Si-111 wafers exhibit similar stress behavior. The degree of c-axis orientation was studied by the authors on both types of Si wafers, and similar results were obtained despite the different lattice mismatch. The very high residual stress often observed in polycrystalline AlN thin films could result in both performance deterioration of electro-acoustic devices as well as decreased lifetime. Substrate deformation and distortion necessarily arise from stresses in the overlying films. In integrated circuit technology, even a slight bowing of silicon wafers may result in significant problems with regard to maintaining precise tolerances in pattern delineation. In addition, film stresses influence band-gap
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e-mail: [email protected] J. Mater. Res., Vol. 18, No. 2, Feb 2003
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shifts in semiconductors, transition temperatures in superconductors, and magnetic anisotropy. Stress-related frequency shifts in acoustic devices were studied by Eernisse2 and Sinha et al.3 Stresses in thin films consist of two major components, namely thermal and intrinsic. Thermal stress results from the different thermal expansion coefficients of film and substrate and is normally induced by the difference in deposition and operation temperatures. The second type, sometimes referred to as intrinsic, residua
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