Determination of Trace Aluminum in High-purity Silicon with Chrome Azurol S Spectrophotometry by Nonlinear Fitting

Spectrophotometry with chrome azurol S is one of the methods used to determine aluminum content in silicon. Since the standard curve is linear but does not pass through the origin, it leads to a large measurement error with low aluminum content. In order to improve the accuracy and decrease the detection limit, the spectrophotometric aluminum standard curve was analyzed in the low Al content part and the effect of different models on the data accuracy is discussed in this paper. Results indicate the absorbance of aluminum standard solution at 0-0.3 μg/mL did not match with the linear relation, while the function of y=17.45230x³+10.42883x²+1.04047x (y for absorbance deduct blank, x for aluminum concentration) yielded good results where R² reached 0.99975. This formula was evaluated by the certified aluminum content in different volume polysilicon solutions. The relative standard deviation is 2.55%. The result matches the one obtained by the inductively coupled plasma atomic emission spectroscopy method. This method can improve the measurement accuracy of low content aluminum in polysilicon when the content of aluminum is greater than 0.55 μg/g.