Die Anwendung radiochemischer Untersuchungsmethoden auf die Probleme der Halbleiter- und Reinststoffanalyse

Abstract

With ultrapure materials it is necessary to investigate, among other parameters, the impurities and the local distribution of impurities and doping elements. Activation analysis techniques have proved highly suitable for this purpose, their advantages being extreme sensitivity of detection, a broad measure of freedom from blank values, the application of an absolute method of analysis and simultaneous coverage of a broad spectrum of elements. The capacity of autoradiography for giving inhomogeneities a visible form can be exploited to derive valuable analytical information about 50 elements on the periodic table. By employing radiotracer techniques it is possible to obtain important information leading to the optimization of manufacturing and fabrication procedures. The above advantages and the wide ranging applications of these methods are demonstrated here by way of results from radiochemical investigations of about 30 problems arising from semiconductor technology. Autoradiographs illustrate that doping and impurity elements deposit in swirls, striations and defects in the crystal lattice, e.g. in silicon, quartz, LiNbO₃, and may result in undesirable crystalline properties. Results from activation analyses demonstrate, among other phenomena, the intrinsic gettering effect with oxygen segregations in silicion, the introduction of impurities in ion-implanted materials through sputtering in a vacuum tube, increased take up of impurities under high-pressure oxidation of silicon and the purifying effect of sapphire liquefaction and of controlled silicon solidification. The capabilities of radiotracer techniques are demonstrated by investigations of zone refining and silicon wafer cleaning.