Research On Measurement And Evaluation System Of Sapphire Substrate Surface Topography

Sapphire is a kind of multifunctional crystal material with excellent mechanical,optical and thermal properties,as well as good corrosion resistance and radiation resistance.It is widely used as LED substrate,laser optical system,military optical window,smartphone screen and other fields.There are strict requirements for its surface quality in various application fields,because high-quality surface morphology is the basis to ensure the subsequent application.At present,the mechanical machining in the sapphire substrate production process mainly includes cutting,grinding,polishing,etc.The measurement and evaluation of the surface morphology of substrate in each process is of great significance for evaluating the processing technology,optimizing the processing flow and effectively controlling the surface quality.In this paper,a special measurement and evaluation system that contains hardware and software was built.It based on the vertical scanning white light interference to meet the needs of the evaluation of sapphire substrate surface micro morphology.The main research contents are as follows:(1)Referring to the five point measurement method in the national standard"measurement method of surface roughness on flat surface of silicon wafer"(GB/T29505-2013),the measurement points(locations)of sapphire substrates of different sizes were determined and the measurement path was planned.According to the evaluation requirements,the typical surface morphology evaluation parameters(two-dimensional parameters Ra,Rq,Rz,Rt,three-dimensional parameters Sa,Sq,Sz,Sp)are selected.Basis on the single point evaluation parameters,the statistical parameters of multi-point evaluation parameters,including:maximum and minimum,mean,variance and standard deviation,are studied to analyze the distribution of substrate surface topography comprehensively.(2)According to the principle of vertical scanning white light interference,a hardware system for measuring the surface topography of sapphire substrate is built.Firstly,according to the measurement requirement of sapphire substrate,a gantry structure was designed with the multi-scale substrate test sample platform.Using marble base,the hardware module of the measurement system is designed,and the optical imaging,micro displacement scanning,displacement table and other components used in the system are selected and integrated.(3)Based on Microsoft Visual C++and OpenCV,the software modules was developed.1)The software modules realized the drive of piezoelectric scanning platform,camera,displacement platform and other hardware equipment,completed the motion control module of the system;2)The collected data is processed using the improved centroid method to recover the three-dimensional shape of the sample surface.Then,extracting the two-dimensional parameters,the three-dimensional parameters and the statistical parameters of the surface topography of sapphire substrate.3)designing the operation interface of the system.(4)The displacement table,piezoelectric scanning table,rotating table and camera field of view were calibrated.After calibration,the field of view of the system is 0.321*0.257mm~2;the output displacement of the piezoelectric scanning platform is about 100nm when the input voltage is 0.1V;the system is calibrated with a standard piece of Ra=0.85?m,and the measurement performance of the system is analyzed;after calibration,the system is verified by experiments,and the 2-inch and4-inch sapphire abraded substrates were measured.The average value of Ra and Sa is0.849?m and 0.869?m for 2-inch sapphire,respectively.The average value of Ra and Sa is 0.887?m and 0.968?m for 4-inch sapphire,respectively.It took about 11minutes and 19 minutes to complete the measurement of 2-inch and 4-inch substrates,respectively.