Optical Sensor for Quality Control of Reflective Surfaces
Thin structures subjected to stresses are frequently encountered in many aerospace and electronic systems. Further, fabrication of electronic and MEMS devices often require quantitative evaluation of substrate and thin film flatness in terms of slopes and curves. For example, silicon wafers that are coated / deposited with thin films introduce thermal and/or mechanical stresses in addition to those caused during manufacturing and service. In such situations, quantification of surface characteristics such as deflection, slope and curvature become important. If not discovered, minuscule deformations can induce poor performance and premature failures for the end user. The high sensitivity of this optical device is capable of identifying defects on a surface that would otherwise go undetected. Follow-on data analysis can obtain detailed topography of measured surfaces. Being able to identify areas of stress and deformity through such analyses can also improve the quality, durability, and overall performance. In applications such as the microelectronics industry, surface stress and deformation can be an invaluable tool in reducing time and costs and improving quality control. The device uses a simple combination of a digital camera, light source, beam splitter and reference target. Image correlation is then used to measure angular deflection of light rays.
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