Depth Profiles of Thermal Donors in Czochralski-Grown n-Type Silicon
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DEPTH PROFILES OF THERMAL DONORS IN CZOCHRALSKI-GROWN n-TYPE SILICON YUTAKA TOKUDA*, TOSHIHISA SHIMOKATA*, MASAYUKI KATAYAMA** AND TADASHI HATTORI** *Department of Electronics, Aichi Institute of Technology, Yakusa, Toyota 470-03, Japan Laboratories, Nippondenso Co. Ltd., Nisshin, Aichi 470-01, Japan
"**Research ABSTRACT
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Depth profiles of thermal donors introduced by heat treatment at 450 C in Czochralski-grown n-type silicon have been studied through capacitancevoltage measurements of Au Schottky diodes in the oxygen concentration 1 7 17 3 range 8.1x10 to 15.3x,0 cm- . Thermal donor concentrations increase with depth and their depth profiles are fitted to the error function equation. The obtained diffusivity decreases with annealing time and is higher for samples with the lower initial oxygen concentrations. Combining with the infrared absorption measurements, it is found that the curves of the diffusivity as a function of loss of interstitial oxygen coincide with each other. The similar tendency is observed on the oxygen diffusivity evaluated with secondary ion mass spectrometry. These results indicate that the oxygen diffusivity at 4501C is related to both the outdiffusion and clustering of oxygen. Depth profiles of thermal donors formed at 650°C are also reported.
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INTRODUCTION
It is well known that thermal donors (TDs) are formed in oxygen-rich, Czochralski-grown (CZ) silicon by annealing around 4500C [1,2]. There are many studies on the properties of TDs so far. The oxygen cluster model is generally accepted for thermal donors. However, it has been pointed out that the enhancement of the oxygen diffusivity by several orders of magnitude is required at TD formation temperatures to explain the TD formation kinetics, as compared to the normal value extrapolated from the high temperature diffusion experiments [3,4]. In fact, Lee, Fellinger, and Chen [5] have observed the enhancement of oxygen diffusivity in the temperature range 500 - 650°C by using secondary ion mass spectrometry (SIMS). Hahn [6] has shown that extended 4501C thermal annealing leads to a low thermal donor concentration layer adjacent to both front and back surfaces. Mathiot [7] has suggested that TDs are self-interstitial agglomerates at 03 complexes to explain the formation of a low thermal donor concentration layer and that the outdiffusion of self-interstitials during annealing leads to the TD depth profiles that TD concentration decreases with decreasing depth near the surface. Wijaranakula [8] has fitted TD depth profiles to the error function equation and determined 13 the diffusivity of silicon interstitials to be on the order of ix1013 2 1.3x10cm /s at TD formation temperatures between 460 and 500*C for 100 h. Thus, it seems still controversial whether TD formation is related to the diffusion of interstitial oxygen or interstitial silicon. In this work, we investigate TD depth profiles formed at 450*C in oxygen-rich n-type silicon. TD depth profiles are fitted to the error function equation. The annealing time dependence of the
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