Z-Distance Measuring System Of Probe Station Based On Automatic Focusing Technology

Wafer testing has become an important process of semiconductor manufacturing,as a core equipment in wafer testing,probe station has been paid more and more attention to its research and development.The Z-distance measurement of the probe station was a prerequisite of ensuring wafer and probe properly aligned.In this paper,we studied the Z-distance measuring system of probe station based on autofocus,completed the overall design of the Z-distance measuring system and develop its key technology.The main contents of this paper include:The first chapter introduced the.research status of the probe station,and summarized the development of auto-focusing and Z-distance measurement technology of probe station.Finally listed the main research contents of this paper.The second chapter introduced the measurement principle of the Z-distance measuring system based on autofocus.Giving the overall scheme of Z-distance measuring system.Designing the visual system and optical system layout of.Finally,designed high precision motion control module.The third chapter introduced the principles and evaluation criteria of autofocus.And analyzed the existing algorithms of time domain method.Compared with various focus function curves,improved "Sobel" algorithm that has better accuracy and higher sensitivity.At the same time,as the algorithm is time domain operation,it has high computational efficiency,and achieved the purpose of focusing fast and accurately.The fourth chapter analyzed the auto focus accelerating algorithm of window selection and extreme point search.Firstly,analyzed the window selection algorithm based on geometric feature,the background and feature information are effectively separated based on the gray histogram of the image.Secondly,improved the climbing algorithm,adaptive variable step size search method,and fit 6 points near the peak.The maximum value in the curve is the position of the quasi-focus.The fifth chapter established the relationship between the image pixels coordinates and the three-dimensional space coordinates.And repeated the Z-distance measuring system of the probe station 30 times and verified the high precision and stability of the system by using the wafer sample.The sixth chapter summarized the main research content and innovation points,and prospected the next step of the research.