No description available.

The self-interstitial defect is commonly regarded as important in regulating diffusion in silicon. A review of the literature reveals that the scientific bases for invoking the self-interstitial defect are weak, while an alternate defect, the vacancy cluster, has been largely ignored. One argument which has been used to establish dominance of the self-interstitial defect over vacancies is based upon attempts to model gold diffusion. Possible behavior of vacancies are considered, and the past analysis is found to be inconclusive. Another argument which has been presented as evidence for presence of silicon self-interstitials is based on observations of type "A" swirl defects. These defects are amenable to interpretation in terms of solidification theory, without need to invoke the interstitial point defect. Two experiments were designed to demonstrate influence of heat treatments upon gold diffusion in electronic grade silicon crystal when the heat treatment was performed prior to gold deposition. Results are interpreted in terms of Ostwald ripening of vacancy clusters retained in the crystal from high temperature processing. / Graduation date: 1996

No description available.

Individual, well structurally characterised dislocations present in n-type silicon have been studied using the electron beam induced current (EBIC) mode of an SEM.</p>An EBIC system has been designed and constructed which includes i) phase sensitive detection, ii) computerised control of the experimental equipment and data capture and iii) a variable temperature SEM specimen stage. With this system measurements have been made of the EBIC contrast of individual segments of deformation induced dislocations produced by two stage compressive deformation at 850°C and 420°C. An experimental and theoretical analysis of EBIC signal generation in the Schottky barrier specimens used in this work is presented. This shows that the EBIC contrast measurements made may be directly correlated to the dislocation recombination strength. Contrast measurements have been made at temperatures in the range 120K to 370K and for electron beam currents from 6 x 10^-12A to 2 x 10^-9A. Several new effects have been observed. Minority carrier diffusion length measurements have also been performed in silicon containing dislocations. These show that the value obtained may depend upon experimental parameters used in a hitherto undetected manner. A new theory describing recombination of carriers at charged dislocations has been developed and this has been extended to provide a description of the variation of the EBIC contrast of dislocations with temperature, electron beam current and also the transient response of the EBIC contrast. Comparison of the theoretical predictions with the results gained experimentally shows full agreement for low temperatures or large beam currents. At high temperatures and small beam currents the theory shows the EBIC contrast will behave differently depending on the density of dislocation states present. Interpretation of the experimental results in terms of this theory allows some new insight to be gained for recombination at dislocations, and values for some of the parameters controlling recombination have been obtained.

Gettering of impurities with oxygen precipitates is widely used during the fabrication of semiconductors to improve the performance and yield of the devices. Since the effectiveness of the gettering process is largely dependent on the initial interstitial oxygen concentration, accurate measurements of this parameter are of considerable importance. Measurements of interstitial oxygen following thermal cycles are required for development of semiconductor fabrication processes and for research into the mechanisms of oxygen precipitate nucleation and growth. Efforts by industrial associations have led to the development of standard procedures for the measurement of interstitial oxygen in wafers. However practical oxygen measurements often do not satisfy the requirements of such standard procedures. An additional difficulty arises when the silicon wafer has a low resitivity (high dopant concentration). In such cases the infrared light used for the measurement is severely attenuated by the electrons of holes introduced by the dopant. Since such wafers are the substrates used for the production of widely used epitaxial wafers, this measurement problem is economically important. Alternative methods such as Secondary Ion Mass Spectroscopy or Gas Fusion Analysis have been developed to measure oxygen in these cases. However, neither of these methods is capable of distinguishing interstitial oxygen from precipitated oxygen as required for precipitation studies. In addition to the commercial interest in heavily doped silicon substrates, they are also of interest for research into the role of point defects in nucleation and precipitation processes. Despite considerable research effort, there is still disagreement concerning the type of point defect and its role in semiconductor processes. Studies of changes in the interstitial oxygen concentration of heavily doped and lightly doped silicon wafers could help clarify the role of point defects in oxygen nucleation and precipitation processes. This could lead to more effective control and use of oxygen precipitation for gettering. One of the principal purposes of this thesis is the extension of the infrared interstitial oxygen measurement technique to situations outside the measurement capacities of the standard technique. These situations include silicon slices exhibiting interfering precipitate absorption bands and heavily doped n-type silicon wafers. A new method is presented for correcting for the effect of multiple reflections in silicon wafers with optically rough surfaces. The technique for the measurement of interstitial oxygen in heavily doped n-type wafers is then used to perform a comparative study of oxygen precipitation in heavily antimony doped (.035 ohm-cm) silicon and lightly doped p-type silicon. A model is presented to quantitatively explain the observed suppression of defect formation in heavily doped n-type wafers.

Mit wellenlängenabhängigen Messungen der Oberflächenphotospannung (Surface Photovoltage, SPV) lässt sich die Diffusionslänge von Ladungsträgern im Volumen von Siliziumproben messen. Das Ziel der Arbeit war es, mit Hilfe temperatur- und injektionsabhängiger Messungen der Diffusionslänge die Natur rekombinationsaktiver Defekte in kristallinem Silizium zu untersuchen. Im Rahmen der Arbeit wurde eine zu diesem Zwecke geeignete Messanlage sowie die nötigen Mess- und Auswerteprozeduren entwickelt. Die Möglichkeiten und Grenzen der aufgebauten Anlage wurden durch Messungen an gezielt mit Eisen, Kupfer oder Chrom verunreinigten mono- und multikristallinen Siliziumproben bewertet. Es zeigt sich, dass die SPV-Methode in einem jeweils begrenzten Temperatur- und Injektionsbereich bei Vorhandensein dominanter Defekte zur Defekt-Spektroskopie einsetzbar ist. Eine Anwendung fand das Verfahren an industriell relevantem, aufbereitetem metallurgischen Silizium (umg-Si).

The thesis deals with the study and analysis of crystallographic defects on the surface of silicon wafers produced by Czochralski method. It focuses primarily on growth defects and oxygen precipitates, which play an important role in the development of appropriate nucleation centers for growth of stacking faults. The growth of stacking faults near the surface of silicon wafers is supported by their oxidation and selective etching. Such a highlighted stacking faults are known as the OISF (Oxidation Induced Stacking Fault). Spatial distribution of OISF on the wafer gives feedback to the process of pulling silicon single crystal and wafers surface quality. Moreover the work describes the device for automatic detection and analysis of OISF, which was developed for ON Semiconductor company in Rožnov Radhoštěm.

Die Rekombinationsaktivität von Versetzungen und Korngrenzen in multikristallinem Silicium wird von Kupfer und anderen metallischen Verunreinigungen wie Eisen mitbestimmt. Das Hauptziel der Arbeit war es, die Verteilung von Kupfer und dessen Wirkung auf die Rekombinationsaktivität von Versetzungen und Korngrenzen genauer zu untersuchen. Dazu wurden optische und elektrische Untersuchungen an gezielt mit Metallen verunreinigten Modellmaterialien durchgeführt. Nicht alle Versetzungen sind rekombinationsaktiv. Es konnte gezeigt werden, dass der Anteil rekombinationsaktiver Versetzungen am Gesamtinventar und die Hintergrunddiffusionslänge von der Verunreinigung mit Metallen abhängig sind. Ergebnisse von Untersuchungen an Proben, die Diffusionsexperimenten unterzogen wurden, deuten auf unterschiedliches Ausscheidungsverhalten von Kupfer und Eisen hin sowie auf Wechselwirkungen mit Versetzungen und Korngrenzen, die mit der Diffusionstemperatur und den Abkühlbedingungen in Zusammenhang stehen.