DENSITY VARIATIONS IN MOLTEN SILICON DEPENDENT ON ITS THERMAL HISTORY

Time-dependent density variations in molten silicon held at 1452 degrees C for about 6 h depended on the thermal process prior to holding. A slow decrease was observed after melting and heating, but a slow increase followed cooling. Melt density reached the same stable value of 2.556 g/cm(3) after both variations. Reflecting this variation, the density of the melt measured during heating was slightly higher than that measured during cooling. The effect of the crucible material on melt density was also studied. With an SiO2 crucible, oxygen impurities of about 10(18) atoms/cm(3) were detected in the resolidified melt. The temperature dependence of the melt density was basically the same as for a SiC-coated graphite crucible, but the anomalous increase in melt density for temperatures near the melting point seemed to be slightly steeper.