Surface Topography Evaluation And Error Compensation Based On White Light Interferometry

With the development of ultra-precision machining technology towards the diversification of machining methods,materials,structures and the intricacy,the demand for accurate characterization and evaluation of surface profile morphology is increasing.As an optical non-contact measuring instrument,white light interferometer is widely used in surface topography measurement.However,the limitation of optical principle in the measurement process often leads to the introduction of measurement results,such as batwing effect,2?error,ghost step and so on.Due to the limitation of diffraction,the measurement results of surface roughness in ultra-precision machining are smaller,and it is impossible to make a correct and effective judgment on the surface machining quality,which affects the feedback and guidance of machining technology,and finally leads to the decline of finished product rate.In this paper,the batwing effect caused by typical surface and the high-frequency error of surface topography measurement results were studied from the measurement principle,virtual model measurement and actual measurement.The influence mechanism of the transverse diffraction limit was clarified.The median filter correction algorithm was proposed to correct the batwing effect and the high-frequency morphology error compensation algorithm based on the transfer function was proposed to correct the lack of high-frequency morphology information,using these algorithms can effectively reduce the contour error and roughness measurement deviation.improve the topography measurement precision and accuracy,effectively evaluate correctly for the surface machining quality,and provide effective feedback processing technology.The specific research contents are as follows:(1)Considering the white light interference bandwidth,the numerical aperture and the morphology of the workpiece,a diffractive simulation model of the white light interferometry process was established to simulate the white light interferometry process,and the sine,triangular and square signals were simulated respectively.The results show that the diffraction effect causes the distortion of the measurement results which is less than the characteristic of the transverse resolution.(2)The proposed simulation model was used to simulate the measurement results of the typical stepped surface topography.The cause of batwing effect was explained from both the simulation and the actual measurement,and the relationship between batwing effect and the real morphology was established.The analysis shows that the batwing effect is affected by the measured morphology,and the batwing effect is obvious when the step height is close to an odd multiple of?₀/4.The discriminant process of batwing effect is proposed.Comparison of three evaluation parameters,the height of the step,the area between the step and the middle line of the contour and the arithmetic mean deviation of the contour,show that the median filter can protect the contour edge and contour information,and its correction effect of batwing effect is better than mean filter.(3)The proposed simulation model was used to simulate the measurement process of the random surface and the grinding silicon wafer surface,and the causes of the surface high-frequency morphology errors were explained from both theoretical and practical measurement aspects.Based on the analysis of the transfer function of the interferometer,a high frequency morphology error correction algorithm is proposed.Finally,the accuracy of surface roughness is improved to more than 90%.