Infrared Photoelastic Study of Thin-Film-Edge-Induced Stresses in Silicon Substrates
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INFRARED PHOTOELASTIC STUDY OF THIN-FILM-EDGE-INDUCED STRESSES IN SILICON SUBSTRATES H. J. Peng*#, S.P. Wong*, Shounan Zhao** *Department of Electronic Engineering and Materials Science and Technology Research Centre, The Chinese University of Hong Kong, Hong Kong, China **Department of Applied Physics, South China University of Technology, Guangzhou, China ABSTRACT The stress distribution in silicon substrates under a silicon dioxide thin film edge, long oxide thin film stripes and long oxide window structures have been studied using the infrared photoelastic (IRPE) method. The experimental IRPE stress fringe patterns were compared with the simulated patterns based on an analytic solution we obtained recently for the stress distribution under a thin film edge in isotropic substrates. Dependence of the stress distribution in these structures on the geometrical parameters such as the stripe width, window width, and substrate thickness were also studied. The implication of a slight discrepancy between the experimental and simulated IRPE patterns on the singular behavior of stress field in the substrate at the film edge and the concentrated force assumption are discussed. INTRODUCTION It is well known in silicon integrated circuit technologies that large localized stresses will be introduced in the silicon substrate near thin film edges and these localized stresses can degrade the device performance by introducing dislocations and defects [1]. Because of its technological importance, over the past few decades, the study of film edge induced stresses in various semiconductor structures, both experimental and theoretical, has continued to attract a considerable amount of research effort [1-7]. The semiconductor structures studied include the local oxidation of silicon (LOCOS) structures [1-3], thin film stripe/semiconductor heterostructures [4, 5], and photoelastic optical channel waveguide structures [6, 7]. Recently, we have obtained an analytic solution for the stress field under a thin film edge in isotropic substrates [8]. The validity of this solution was demonstrated by good agreement between the experimental and theoretical simulated results [8, 9]. In this work, we have studied in detail the stress field in silicon substrates under a silicon dioxide thin film edge, and those under long oxide film stripes and long oxide film window structures using the IRPE method. It will be seen that the experimental results in general show good agreement with the simulated results using our analytical solution. A slight discrepancy between the experimental IRPE stress fringe pattern and the simulated pattern will be discussed in terms of the validity of the concentrated force assumption for the thin-film-edge-induced stress problem. EXPERIMENT Thermally grown SiO2 films of about 1 µm thick on n-type (100) Si wafers with resistivity of 115 Ωcm were prepared using standard techniques. Patterned SiO2 film structures including simple film edges, long stripes and long windows of various width were prepared using standard photolitho
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