| Films are widely used in industrial products and daily necessities such as LCD screens,photographic lenses,mirrors,etc.The thickness of the film is one of the most important indicators that affect the performance of the film.The existing film thickness measuring methods(ellipsometers,reflective thickness gauges,etc.)are limited to single-point measurement,and cannot meet the needs of the production workshop for large-area scanning inspection of thin-film products.Line imaging measurement can obtain hundreds of points' data on one measurement at the same time.Therefore,in large-area scanning measurement,the efficiency of line imaging measurement is much higher than single point measurement.This article studied the line imaging film thickness measurement system,and extended the reflection spectroscopy method,which is one of the film thickness measurement methods,from single-point film thickness measurement to line imaging film thickness profile measurement.The main contents include:(1)Designed an imaging spectrometer with a spectral range of 400-700 nm,simulated with Zemax software,and built a prototype.Using characteristic spectroscopy to achieve spectral calibration.And the FWHM of a 488 nm laser was measured equal to 0.66 nm,which met the design index of 1nm's spectral resolution.Using polynomial coordinate transformation to achieve distortion correction.The polynomial coordinate transformation and bilinear grayscale interpolation method of the photos' distortion correction are applied to the distortion correction of the imaging spectrometer.And proposed a method of constructing the standard coordinate system of the spectral image by using a special slit,which solves the problem that the imaging spectrometer can't find a normal way to get the standard coordinate system.The corrected spatial dimension distortion is less than 15?m,spectral dimension distortion is less than 10?m.The imaging spectrometer has reached the level of some commercial imaging spectrometers and spends less cost.(2)A line-imaging film thickness profile measurement system based on Kohler illumination and spectral analysis was designed.The line-imaging reflection spectrum of a 495.4nm thick Si O2 film(Si substrate)sample was measured.The LM algorithm(known refractive index)was used to data processing.Film thickness data of 120 spatial dimensional channels were extracted in one line-imaging measurement.The average film thickness was 496.56 nm,and the measurement error was 1.16nm(0.234%).The film thickness profile was within the range of 496.56nm±2nm(0.4%).30 times repeatability measurement error 0.55nm(0.11%),indicating that the line-imaging film thickness profile measurement system in this paper can accurately and stably measure the line profile thickness of the film.The single film thickness line profile measurement(120 spatial dimension channels)takes an average of 1.05 seconds,and the average time of each channel measurement is 0.00877 seconds,which is 6.5% of the average single-point measurement time of 0.1354 seconds.The measurement efficiency is 15 times that of the ordinary single-point film thickness measurement system.This paper has designed a lens imaging spectrometer,and proposed a simultaneous correction algorithm for the spatial and spectral distortion of the imaging spectrometer based on polynomial coordinate transformation and bilinear grayscale interpolation.The imaging spectrometer after distortion correction has reached some commercial imaging spectrometers.Relying on the designed imaging spectrometer,this paper has designed a line imaging film thickness measurement system based on Kohler illumination and spectrum analysis,which can accurately and stably measure the film thickness profile.The average measurement time per channel is 6.5% of the time for ordinary single-point measurement,which improves the rate of film thickness profile measurement.It provides guidance for improving the efficiency of scanning and measuring the large area thickness profile required for film roll-to-roll production. |
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