The Computer Simulation And Nondestructive Testing Of Sapphire Wafer By Laser

Because of its superior optical and mechanical properties, Sapphire is widely used in new microelectronic industry, aerospace industry, military and other fields.However, all of applications to Sapphire need high quality, due to the high hardness and many processes of proceed into sapphire wafer which inevitably remained complex and diverse defect. The high-quality sapphire products require to not only have no macroscopic defects include scratches, bubbles etc, but also have no micro /submicron defects, even the micro / submicron defects is difficult to detected by normal methods. In order to detect the micro / nano defects in sapphire wafers exactly,efficiently and nondestructively, this thesis aims to study use the spatial distribution of scattering intensity to analysis and detects the micro defects of sapphire wafer, and it is the the core part of the device; then based on the results of calculated simulation and the comparison of transmission spot, we designed a simple defect nondestructive testing device.(1) With reference to the generalized Lorenz- Mie scattering theory, based on the profound discussion of the interaction between spherical particles and laser, we proposed a new way to use the scattering distribution in different area to detect the defects of sapphire wafer and establishing a mathematical model between a visible laser and micro bulk defects of sapphire wafer which lay a foundation to detect its internal defects.(2) Based on the generalized Lorentz- Mie theory to have arithmetic researching and numerical calculating. Firstly, by comparing scattering signals among back scattering, forward scattering, vertical scattering, the optimum angle to receive scattering light is ? = ? / 2. Then simulation of different different relative refractive index and different scattering body, the size of defect as the main factor to affect the distribution of spatial light intensity is noted.The last, by analyzing scattering light distribution in fixed spatial to the same relative refractive index and different sizes of defects, the maximum values of scattered light intensity values in fixed spatial as the first characteristic value, and the cut-off frequency as the second characteristic can be used to determine the size of the defect.(3) In order to make the inspection system to sapphire wafer more efficient. After observing transmission spot between defects and the reference samples, then putting forward the visual comparison of transmission spot to judge the defects more thanseveral hundred microns initially. And it can be used as a preliminary screening of the wafer defect detection system to screen out the "big size" defects.(4) Based on theoretical directions, a simple Nondestructive Testing to sapphire wafer is designed. The detecting system is made up of helium-neon laser,scanning system,HD CCD,scattering light signal collect unit and scattering light signal proceeding unit, etc.