The Influence of Stresses on the Surface-Near Defect Structure
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THE INFLUENCE OF STRESSES ON THE SURFACE-NEAR DEFECT STRUCTURE
M. REICHE* AND W. NITZSCHE** * Max-Planck-Institut fur Mikrostrukturphysik, Weinberg 2, D - 0 4050 Halle/S., Germany ** Institut fuir Festk6rperanalytik und PartikelmeBtechnik, RudolfstraBe 47, D - 0 5023 Erfurt, Germany
ABSTRACT An external stress field, induced at the film edge of a nitride layer, affects the defect generation in the surface-near region. Nucleation and growth of oxide precipitates and/or the generation of dislocations result in the reduction of the width of the denuded zone. The defect formation is discussed in dependence on the stress, gettering technique (annealing conditions), and on the initial oxygen concentration. The effect on electrical parameters is shown. The investigations prove that an additional oxide film (SiO2/Si 3 N4 films) does not relax completely the tensile stress induced by the nitride layer.
INTRODUCTION The defect formation in the volume and surface-near region of silicon wafers have been widely investigated in dependence on different annealing cycles applied for intrinsic gettering. Here, especially the influence of the material parameters - such as the impurity concentrations (oxygen, carbon), thermal history etc. - and annealing conditions (temperature, and annealing time etc.), were studied in detail (e.g. [1,2]). On the other hand, only a few is known about the influence of external variables on the formation and stability of defects induced by gettering techniques. External variables may be e.g. oxidation processes or doping (both connected with the injection of a high concentration of silicon self-interstitials (Sii) into the wafer volume), and the deposition of layers causing the formation of stress fields in the surface-near region. They characterize typical device processes. Alterations of the defect structure and the denuded zone induced by these variables are therefore also a measure of the efficiency of the applied gettering technique during the whole fabrication process. The present paper describes investigations especially to the influence of stress fields. They are caused by the deposition of SiO2/Si3N4 layers, generally used as masks for LOCOS techniques. For intrinsic gettering, the so-called ramping technique has been applied, which make it possible to obtain specific types and densities of defects [3]. Moreover defect reactions, as pinning of dislocations on impurity clusters, refer that high supersaturations of point defects (Sil) act during these processes.
EXPERIMENTAL Boron-doped wafers (p = 12 - 20 Qcm, (100) orientation, diameter 4 in.) were used for the experiments. The preparation follows typical MOS conditions. After the first oxidation (H2/O2 plasma, 8000 C) a Si 3N 4 layer was deposited by LPCVD at 8000 C (deposition rate 4 nm/min). In order to modify stresses the thicknesses of the oxide layer, doxl, and of the nitride layer, dni , were varied: (i.) doxi= 40 nm, dni = 70 nm (ii.) doxI = 20 nm , dni = 150 nm Mat. Res. Soc. Symp. Proc. Vol. 262. 01992 Materials Research Society
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