Optical Scatter—Techniques and Analysis
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Optical surfaces of components in lasers, telescopes, cameras, and eyewear, and Si wafers with nanometre devices in the semiconductor industry are fabricated to increasingly rigorous standards to improve performance, quality, and yield. This trend necessitates the development of novel techniques, innovative technology, and integrable systems for the detection and evaluation of defects and inaccuracies at nanometre levels. Surface metrology must be achieved at high-speed, utilizing synergism of rapid sampling, low noise data acquisition, analytical software, and graphics. Intelligent monitoring of various parameters, operating concurrently with fabrication processes in feedback loops, could converge industrial systems to true nanoscale production. Optical scatter is a viable inspection technique utilized in photonics and semiconductor manufacturing, where optics and Si wafers are scanned in entirety, within a matter of a few minutes, to produce detailed maps of defects, device irregularities, surface roughness, shape inaccuracies, and thin film composition. We explore advanced concepts and technology based on optical scatter measured in triangulation off a target surface with a passive sensor, integrated with nanometre scanning capability, and real-time software analysis to measure and resolve various operating parameters in industrial environments, in conjunction with the physical quality of the finished product. Our results demonstrate the limitations of contemporary manufacturing with a view to future development and process optimization, leading consistently to true nanoscale accuracy. The techniques presented herewith are tractable, and can easily be configured for the manufacture of sub-µm semiconductor devices to large meter-size optics.
KeywordsOptical scatter Optical surfaces Semiconductor wafers Laser triangulation Noise error Defects Thin films
Financial and/or technical assistance for this work was provided from several sources at various times, including the US Naval Research Laboratory, California Institute of Technology, US Air Force, NASA—Jet Propulsion Laboratory, the Livermore Laboratory, the National Research Council; and is in dedication to Esmeralda and Benjamin Soãres. Dr. Brian Limketkai and Dr. Payam Pakzad at Caltech provided helpful experimental assistance in this project. Additional assistance was provided by Dr. Andrew Huntington and Dr. Neil Jones at Caltech.
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