The Key Technology Research Of Phase-shifting Digital Holography On The Detection Of ITO Substrates

With the rapid development of electronic products,touch screen,especially the capacitive touch screens enter there prime time for development.The ITO(Indium Tin Oxides)glass substrate is an important part of the capacitance touch screen.The detection of the disfigurement of the ITO line directly affects the quality of the capacitance touch screen.However,as the pattern of the ITO glass substrate becomes more and more complex,the circuit becomes more and more fine,the disfigurement scale needs to be detected is getting smaller and smaller.For ITO lines with high transparency,it is difficult to detect effectively of the circuit disfigurements.This paper proposes the phase-shifting digital holography method for detecting disfigurements in ITO glass substrates.This method using the phase-shifting digital holography to image the ITO line pattern,which avoids the condition that the ITO line must have a certain contrast in the conventional imaging detection.As long as there is a certain three-dimensional shape change or refractive index difference between the ITO line and the glass substrate,the phase distribution of the light field can be reproduced by phase-shifting digital holography,and then realize the clear imaging of the ITO line.This paper mainly studies the key technology of phase-shifting digital holography in the measurement of ITO glass substrate,and focuses on analysis and test verification of the factors affecting the measurement of ITO line morphology.It provides theoretical and experimental support for the large batch reproduction and detection of the phase-shifting digital holography in the ITO glass substrate industry.Main achievements are as follows:1、 The current development of the touch screen is investigated,the rapid development trend of the touch screen and the more and more fine line characteristics are pointed out,which lead to the urgency of the disfigurement detection requirement for ITO glass substrate.The status of ITO detection technology is investigated,and the advantage of phase-shifting digital holography for disfigurement detection of ITO glass substrate is analyzed.2、 The basic principle of each step in the phase-shifting digital holography is described in detail.The main phase shift methods and devices are described,and the principle of phase shift implementation is analyzed.According to Nyquist sampling theorem,the conditions of digital hologram recording are analyzed.The principles of fixed step phase shift algorithm,equal step phase shift algorithm and random step phase shift algorithm are introduced.The diffraction theory used in the reconstruction of phase-shifting digital holography is analyzed.3、 For the polarization phase shift device,a theoretical model is established,and the influence of the non verticality of the polarizer and the laser axis on the phase shift accuracy is analyzed.A method of calibrating the verticality of the polarizer using autocollimator is proposed,which greatly reduces the influence of the mounting attitude of the polarizer on the phase shift precision in the light path.A method for accurately controlling the phase shift amount by using the theodolite and the plane mirror is proposed,so that the phase shift control precision reaches the angular second level.For the two step phase shift method with fixed step length,a phase shift control evaluation function based on the statistical information of hologram is proposed,which can make the phase shift accurately controlled to π/2.For the random step length phase shift method,a phase shift quantity extraction algorithm without iterative computation is proposed.4、 The factors affecting the interference fringes drift of hologram are analyzed,and the characteristics of the periodic and continuous disturbances are pointed out.The method of frequency domain filtering for single pixel points is proposed,which eliminates the influence of the disturbance of mechanical vibration and the change of air refraction on phase-shifting digital holography and enhances the adaptability of phase-shifting digital holography in industrial measurement.5、 On the pre amplified holographic recording mode,the problem that the parallel light wave becomes spherical wave under the influence of using collecting mirror and microscopical lens in the optical path,then the additional phase of the interference field is generated.The effect of the collecting mirror aberration on the additional phase is analyzed,and the corresponding theoretical model of the spherical aberration and the additional phase is established.The method of using the phase distribution at no-load,fitting the additional phase surface according to the theoretical model,and performing digital correction is carried out.The experimental verification is made to illustrate the validity of the spherical aberration distribution theory model.6、 Based on the phase shift control method,the hologram stripe drift filtering method and the additional phase elimination method which are put forward in this paper,the ITO phase-shifting digital holography test platform is built,and the ITO line is holographically measured.And then the reconstructed phase distribution is compared with the traditional laser illumination,which illustrate the effectiveness and superiority of digital holography in ITO line measurement.7、 Several important error sources of phase measurement are analyzed,including the phase shift error,vibration error,detector nonlinear error and the light source instability error,and there influence mechanism and expression form are described.According to the specific test conditions of this paper,the magnitude of the error source is estimated,and a specific error theory model is derived for each error source,and the effect of each error source on the phase measurement is estimated.