Measurement of Active Components in Wafer Cleaning Solvent using Near-Infrared Spectroscopy

Abstract

The feasibility of measurement of chemical components in wafer cleaning solvent studied using NIR spectroscopy. The cleaning solvent is composed of ammonium hydroxide (NH4OH), hydrogen peroxide (H2O2) and water. The normal concentration of NH4OH and H2O2 is normally 1% in volume. Since the concentration of these two components should be constantly maintained for optimal cleaning of silicon wafers; therefore, continuous and on-line measurement is necessary. All three components had hydroxyl groups, so the corresponding bands (centered at 6800 cm-1) were overlapped each other. In the case of NH4OH, a distinguishable and non-overlapping N-H bond at 4500 cm-1 was used for calibration without difficulty. For H2O2, its O-H band overlapped with that of water; however, its position was slightly different from that of water. When H2O2 concentration is increased, its O-H band shifted to the lower frequency. Therefore, this small spectral difference was used for calibration of H2O2. PLS (Partial Least Squares) regression was used for overall calibration. Based on calibration results, the measurement of active components in wafer cleaning solvent is feasible and optical fiber spectrometer system will be evaluated for on-line and remote analysis.