Hydrogen Induced Defects at Silicon Surfaces and Buried Epitaxial Misfit Dislocation Interfaces
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HYDROGEN INDUCED DEFECTS AT SILICON SURFACES AND BURIED EPITAXIAL MISFIT DISLOCATION INTERFACES Tian-Qun Zhou, Zbigniew Radzimski, Zhigang Xiao, Bhushan Sopori*, and George A. Rozgonyi Dept. of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695-7916 *Solar Energy Research Institute, 1617 Cole Boulevard, Golden, CO 80401 ABSTRACT A silicon epitaxial structure containing spatially confined arrays of misfit dislocations has been used in order to investigate the interaction between hydrogen and individual extended defects. Hydrogen was introduced using a Kaufman plasma ion beam source. A characteristic Si-H peak at 2100 cm- 1 was obtained using multiple internal reflection infrared spectrophotometry. Microdefects such as gas bubbles and {1111 planar defects were found near the surface, as well as at the misfit dislocation interfaces, using transmission electron microscopy. A heavily damaged region was obtained on the top Si surface and an extended area SEM/EBIC contrast was obtained due to a surface electrical field. INTRODUCTION The effect of hydrogen on the electrical properties of silicon has become an important issue due to its ability to passivate, at moderate temperatures, both shallow impurities and deep-level defects[l]. Hydrogen can tie up silicon dangling bonds or distorted silicon bonds at dislocations and grain boundaries, thereby making them electrical inactive[ 2 ,3]. Controlled hydrogenation is usually done by exposure of the silicon surface to a hydrogen plasma source; however, the chemically active and energetic hydrogen ions can also induce surface degradation by introducing extended defects during the plasma process[ 4 -6l. In this paper, we present chemical, structural and electrical data on hydrogen plasma treated silicon wafers containing buried sheets of interfacial misfit dislocations. EXPERIMENTAL In this study, two types of silicon crystal were used. One was a virgin (Ill) oriented silicon wafer, while the other was a (100) epitaxial silicon wafer with a buried Si(Ge) layer. The epitaxial Si(Ge) layer contained two buried interfaces with misfit dislocations which act as gettering sites for metal impurities or hydrogen[7,8]. The silicon layers were grown by adding approximately 2% GeH 4 to a SiCl 2 H 2 CVD reactor. The misfit dislocation node density is easily adjusted from 106 to 108 by varying the gas phase ratio of GeH 4 to SiCi 2 H 2 from 1% to 4%, or adjusting the Si(Ge) epitaxial layer thickness. The samples were anisotropically etched with KOH:H 2 01 9 ] following growth of 70 nm thermal oxide and opening 10 pm Mat. Res. Soc. Symp. Proc. Vol. 163. ©1990 Materials Research Society
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Fig.1 Schematic Diagram of Anisotropically Etched Groves in Oxidized Epitaxial silicon with Misfit Dislocations wide windows on 500 gtm wide centers, as schematically shown in Fig.1. In this way, misfit dislocation end points could be exposed along the (111) side walls of an etched trench, while the 70 nm cappi
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