The role of surface-tension-driven flow in the formation of a surface pattern on a Czochralski silicon melt

Spoke patterns on shallow silicon melts and polygonal cellular patterns on the surface of Czochralski (CZ) silicon melts were observed by CCD camera. The dark stripes of the spoke patterns in the CCD images indicate the lower temperatures. We found that the number of spokes depends on the depth of t he silicon melt. When the thermocapillary flow in a 3-mm-deep silicon melt was dominant, a spoke pattern was clearly observed on the surface. On a CZ silicon surface of a 200-mm-deep melt not under a vertical magnetic field, polygonal-shape patterns were observed to move toward the melt center. Howe ver, under a vertical magnetic field, the polygonal patterns only changed t o be more longitudinal but did not disappear. These observations indicate t hat the surface flow of a CZ melt and its instability cannot be fully suppr essed by a magnetic field and that the surface flow plays a significant rol e in forming the surface patterns. (C) 2001 Elsevier Science B.V. All right s reserved.