Relationship Between Strained Silicon-Oxygen Bonds and Radiation Induced Paramagnetic Point Defects in Silicon Dioxide
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RELATIONSHIP BETWEEN STRAINED SILICON-OXYGEN BONDS AND RADIATION INDUCED PARAMAGNETIC POINT DEFECTS IN SILICON DIOXIDE W.L. Warren, P.M. Lenahan, C.J. Brinkerwand C.S. Ashley* The Pennsylvania State University.,University Park, PA 16802 *Sandia National LaboratoriesAlbuquerque, NM 87185
ABSTRACT We have investigated the radiation induced generation of paramagnetic point defects in high surface area sol-gel silicates containing various concentrations of the Raman active 608 cm*I D, "defect" band attributed to cyclic trisiloxanes (3 membered rings). Our results indicate that strained silicon-oxygen bonds due to three membered rings are the dominant E"(trivalent silicon center) and paramagnetic oxygen center precursors at high irradiation doses for silicates containing large concentrations of the D2 species. These results directly demonstrate that atomic level stress does play a role in the radiation damage process of silicon dioxide. INTRODUCTION Silicon dioxide is one of the most important materials used in microelectronic and optical fiber technologies. It has long been recognized that Si0 2 can be damaged by ionizing radiation [1-4]. Ionizing radiation affects the insulating layers of metal oxide semiconductor field effect transistors (MOSFET's) [1,2] as well as the transmission properties of low loss optical fibers. Thus, a detailed understanding of the radiation induced defects (and precursors) in silicon dioxide is of considerable interest. Electron spin resonance (ESR) is generally recognized as the most sensitive probe of atomic defect structure in amorphous silicon dioxide. Extensive ESR studies have been performed on quartz and bulk amorphous silicon dioxide subjected to various forms of irradiation (x-rays, gamma rays, and neutrons) [4-8]. These investigations have identified several intrinsic point defects; the most extensively investigated of which is the E' center. The E' center is an unpaired electron highly localized on an sp3 hybridized orbital of a silicon backbonded to three oxygens [6,7]. One theoretical model identifies the E" center as a hole trapped at the site of an asymmetrically relaxed oxygen vacancy [9,10]. The positive charge state of oxygen vacancy E' centers in gamma irradiated thermally grown silicon dioxide films on silicon was experimentally established by Lenahan and coworkers [11,12]. ESR studies of irradiated fused silica glasses have also identified two intrinsic paramagnetic oxygen centers, namely the peroxy radical (O-0-Si-03) and the non-bridging oxygen center t0-Si-0 3 ) [4,8]
Mat. Res. Soc. Symp. Proc. Vol. 180. 01990 Materials Research Society
248
In this study we report evidence for a new E' and paramagnetic oxygen center precursor [13] - a structure involving strained Si-0 bonds; to obtain this information we used Raman scattering and ESR experiments. It should be mentioned that for years people have proposed models involving atomic level stress in the radiation induced damage process in silicon dioxide [14-16]. The motivation for this work was to establish if atomic
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