An object of the present invention is to measure a carbon concentration with a small number of calibration curves for silicon wafers containing oxygen at a high concentration. A calibration curve determination method includes: a step (S11) of providing a plurality of wafer groups each including a plurality of silicon wafers having the same oxygen concentration and different carbon concentrations, the wafer groups being different from each other in the oxygen concentration of the silicon wafers included therein; a step (S12) of irradiating a plurality of regions of each of the silicon wafers with electron beams at different irradiation doses; a step (S13) of obtaining, by a photoluminescence (PL) method, an intensity ratio of a first luminescence intensity deriving from silicon to a second luminescence intensity deriving from carbon for each of the regions; a step (S14) of classifying obtained data into a plurality of data sets and creating a first calibration curve for each data set, the data included in each of the data sets having the same irradiation dose and the same oxygen concentration, and the data sets being different from each other in at least one of the irradiation dose and the oxygen concentration; a step (S15) of selecting a pair of the first calibration curves which are equal to each other in the irradiation dose and different from each other in the oxygen concentration, and obtaining a difference between slopes of the paired first calibration curves on a log-log plot; and a step (S16) of creating a second calibration curve using all of the data contained in the data set used for creating the selected first calibration curve.
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