Crystal Growth from the Melt

The bulk single crystals of semiconductors (e.g. Si, GaAs) and oxides which are at present commercially produced have mostly non-uniform properties in the microscale (e.g. doping striations) and in the macroscale (longitudinal and lateral segregation). Such inhomogeneities are deleterious for the performance of the devices produced from these crystals. This book gives a review of the various origins of inhomogeneities occuring during crystal growth. It is shown that convection is the major source of the non-uniformities in the technically used growth configurations, e.g. Czochralski-, zone- and Bridgman-methods, because the growth rate is controlled by the heat transport. The formalism of hydrodynamics, especially dimensionless numbers, is used for a modeling of melt growth, giving a correlation between the occurrence of inhomogeneities and relevant growth parameters. The results of the theoretical and experimental modeling are found to correlate with results of real crystal growth, especially for cases of dominating buoyancy convection. Various measures in avoiding inhomogeneities are derived from the models and are discussed with respect to their efficiency and practical applicability.

1 The content ofthis article is based on a German book version ) which appeared at the end of the year 1986. The author tried to incorporate - as far as possible - new important results published in the last year. But the literature in the field of convection and inhomogeneities in crystal growth from the melt has increased so much in the meantime that the reader and the collegues should make allowance for any incompleteness, also in the case that their important contributions have not been cited. This could for example hold for problems related to the Czochralski growth. But especially for this topic the reader may be refered to the forthcoming volume of this series, which contains special contributions on Surface Tension Driven Flow in Crystal Growth Melts by D. Schwabe and on Convection in Czochralski Melts by M. Mihelcic, W. Uelhoff, H. Wenzl and K. Wingerath. The preparation of this manuscript has been supported by several women whose help is gratefully acknowledged by the autor: Mrs. Gisela Neuner for the type writing, Mrs. Abigail Sanders, Mrs. Fiona Eels and especially Prof. Nancy Haegel for their help in questions of the English language and Mrs. Christa Weber for reading corrections. Also the good cooperation with the Springer Verlag, especially Mrs. Bohlen and with the managing editor of Crystals, Prof. H. C. Freyhardt, who critically read the manuscript, is acknowledged.

From the Contents: Fundamentals of the Process Modeling for Semiconductor Crystal Growth.- Macroscopic Inhomogeneity.- Avoidance of Macroscopic Inhomogeneity.- Microscopic Inhomogeneity.- Unsteady Buoyancy Convection as an Origin of Microinhomogeneity.- Measures to Avoid Convection Induced Microinhomogeneity.- Concluding Considerations for an Optimization of Crystal Growth Configurations.