Abstract
To suggest a guiding principle for oxygen uniformity in CZ silicon single crystals, two kinds of experiments from a viewpoint of SiO evaporating from free surface of the melt were examined. First, evaporation rate of SiO from silicon melts with different aspect ratio were measured as a function of A_C/A_S(A_C: contact area between melt and silica crucible, A_S: area of free melt surface) by using thermogravimetric method. The evaporation rate of SiO increased with increasing A_C/A_S, while showing strong temperature dependence. Next, several CZ crystals with varying diameters were grown by the two characteristic growth conditions: the "speed control" and the "temperature control" respectively. These conditions could control the SiO evaporation rate quasi-quantitatively during the crystal growth by changing A_C/A_S It should be noted that axial and radial oxygen distribution in the " speed control" crystal largely varies as a function of A_C/A_S. On the contrary, oxygen was uniformly distributed in the "temperature control" crystal . It was revealed that the marked oxygen heterogeneity in the " speed control" crystal was mainly originated in the variation of SiO evaporation due to high temperature of the melt. Regarding to the influence of boron upon the oxygen distribution in CZ silicon crystals, the oxygen heterogeneity was remarkably emphasized since boron enhanced the evaporation of SiO. It was concluded that fluctuation of SiO evaporation and thus variation of oxygen concentration in silicon melt should be suppressed for oxygen uniformity in silicon single crystals.
