Importance

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Abstract

Calibration curve data is collected by measuring transmitted light intensities of a treating solvent while solvent temperature is varied. Also measured are a standard transmitted light intensity (transmitted light intensity of a standard treating solution prepared at a predetermined concentration and temperature) and a reference transmitted light intensity (transmitted light intensity of the solvent). Estimated transmitted light intensity of the solvent when its temperature is the same as that of the standard treating solution, is derived from the temperature of the standard treating solution and the calibration curve data stored. A correction factor is computed from a ratio between the reference transmitted light intensity and estimated transmitted light intensity. Then, transmittance of the standard treating solution (standard transmittance) is computed from the standard transmitted light intensity, reference transmitted light intensity and a correction factor. Subsequently, transmitted light intensity of a treating solution for actual use in treating substrates (sample transmitted light intensity) is measured. A sample transmittance of this treating solution is derived from the sample transmitted light intensity, reference transmitted light intensity and a correction factor. Concentration of the treating solution is controlled based on the standard and sample transmittance.

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First Claim