Online Measurement Of ITO Film Thickness Profile Based On Line Imaging Spectral Analysis

Indium tin oxide(ITO)film is a kind of semiconductor material with excellent light transmittance and conductivity.It has been widely used in solar cells,liquid crystal displays,energy-saving glass and anti fog and frost windows.The thickness of ITO film is one of the key factors affecting its photoelectric properties.At present,photoelectric extremum method and quartz crystal oscillating method are widely used in on-line monitoring of ITO film thickness.The photoelectric extremum method is based on the periodic variation of reflectivity or transmittance with film thickness.However,the monitoring accuracy is not high due to the slow change of transmittance or reflectivity near the extreme point.Quartz oscillating crystal method is to monitor the film thickness by the change of the natural frequency of quartz crystal,but it directly measures the quality of the film,and the film density and refractive index depend on the preparation conditions,which is not reliable for calibrating the crystal monitor.Aiming at the deficiency of on-line monitoring of ITO film,this paper proposes a method to realize on-line monitoring of ITO film profile thickness.In this method,the single point measurement of film thickness by reflection spectroscopy is extended to the measurement of film thickness profile,and the multi-point measurement of film thickness is realized by obtaining the line imaging two-dimensional spectrogram of the film.The main research results and conclusions are as follows:(1)The characterization methods of ITO film thickness are classified and summarized,including high-precision measurement in laboratory environment and film thickness monitoring in production line.The advantages and disadvantages of different methods are analyzed,and an on-line monitoring method of ITO line profile film thickness based on line imaging spectral analysis principle is proposed.(2)Based on the principle of reflection spectrum measurement and line imaging,a set of line profile film thickness measurement system is designed and built,including hardware part and data processing part.The hardware part includes Kohler illumination light path,imaging light path and transmission imaging spectrometer.Data processing includes spectral calibration of transmission imaging spectrometer,image distortion correction and film thickness profile calculation.Based on the characteristic spectrum method,the spectrum calibration is completed.The polynomial coordinate transformation method and bilinear interpolation method are used to correct the distortion of two-dimensional spectrogram.The thickness of the film line profile was fitted by combining the reflectance spectroscopy and LM algorithm.(3)Standard SiO₂ thin film measurement experiment.Based on the film thickness profile system,three standard SiO₂ film samples with thickness ranging from 20 nm to 500nm were measured.The measurement error of each sample is less than 2 nm,and the accuracy of the system is high.A CCD spectrometer is used to measure the film thickness of standard SiO₂ film samples at a single point.Compared with the experimental data,the average single point measurement time of the line profile film thickness measurement system is only 6.4%of that of the CCD spectrometer,and the system has high measurement efficiency.(4)Complete the measurement of ITO film.The thickness of ITO film was measured in the range of 50?300 nm.The average measurement time of the profile film thickness of the sample line is 0.8754 s,and the average single point measurement time is 0.0073 s.