シリコン単結晶の酸素濃度均一性と融液の蒸発

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To relate oxygen distribution in CZ silicon single crystals with evaporation of oxide species from free melt surface, several basic investigations were executed paying attention to influence of doping impurity added into the melt. Chemical species evaporating from silicon melt doped with boron and their evaporation rate were examined. It was clarified that boron assisted the evaporation of SiO from the free melt surface. In order to understand heat transport at free surface of silicon melt, influence of antimony addition on temperature of the free melt surface was studied and an approximate estimation for the latent heat of evaporation species was carried out. Based on the results obtained in these basic studies, two kinds of experiments were examined in order to suggest a guiding principle for oxygen uniformity in CZ silicon single crystals. First, evaporation rate of SiO from silicon melts with different aspect ratio was measured as a function of Ac/As (Ac : contact area between melt and silica crucible, As : area of free melt surface) by using thermogravimetric method. The evaporation rate of SiO increased with increasing Ac/As, 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 Ac/As. It should be noted that axial and radial oxygen distribution in the "speed control" crystal largely varies as a function of Ac/As. 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.
湘南工科大学の論文
2001-03-18

シリコン単結晶の酸素濃度均一性と融液の蒸発

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