DENSITY ANOMALY EFFECT UPON SILICON MELT FLOW DURING CZOCHRALSKI CRYSTAL-GROWTH .2. TIME-TOPICAL FLOW STRUCTURE UNDER THE GROWTH INTERFACE

The purpose of this work is to investigate the effect of density anoma ly upon the time-topical structure of the melt flow under the crystal growth interface by applying a wavelet transform to the temperature fl uctuation in this region. The fluctuation components that have a perio d of about 44 seconds appear irregularly on the time axis and are cons idered to be caused by detachment of the boundary layer near the botto m of the crucible in the case of a relatively deep melt, This is the c haracteristic phenomenon of ''soft turbulence'', as described in a pre vious paper [Togawa et al., J. Crystal Growth 160 (1996) 41]. These fl uctuation components disappear when gallium is added to the shallow me lt, whereas the flow structure remains turbulence-like in the cases of undoped and B-doped shallow melts. A detailed statistical analysis of this time-topical flow structure showed that this flow regime stays u nsteady and the flow situation changes from moment to moment. When gal lium is added, the flow structure becomes laminar-like and differs cle arly from the other two cases. We can thus confirm the existence of a silicon melt density anomaly in the crystal growth system and its infl uence upon the flow structure.