High Speed Instrumentation for Inspection of transparent parts

Abstract

In micro manufacturing (MEMS, polymer hot-embossing, polymer roll-to-roll imprint, etc.) precise micro and nano-sized features are distributed over large areas. In order to inspect for defects or employ statistical process control on micromanufactured parts, metrological instruments must collect data with submicron resolution at a rate fast enough to keep up with the pace of production. Commercial inspection instruments fall short on meeting these challenging demands. This doctoral thesis details the design, implementation, and results of an optical system built to provide real-time inspection for transparent polymer microfluidic devices. Our instrument utilizes a high speed camera (500 fps) in conjunction with submicron precision positioning stages (20 nm resolution) to rapidly collect topological data on the microfluidic devices. The stream of images are processed using a depth from focus technique to provide surface inspection with 0.5 micron lateral resolution and 1 micron vertical resolution at an inspection speed of 640,000 voxels per second. The instrument also demonstrates the ability to measure vertical sidewalls as a result of the tilted orientation of the camera system providing access to these typically hidden or eclipsed areas. The 3D contour plots generated by the instrument are used to characterize a manufacturing process demonstrating automatic defect detection, repeatability analysis, and run charts that can be used in process control. This thesis also explores the design and experimentation of a novel sensor that can simultaneously measure the thickness and lateral position of a transparent object. This capability is especially useful to control the lateral position of a transparent web with a feedback system during a manufacturing roll to roll process. The sensor measurement has demonstrated submicron repeatability over millimeters of range in both thickness and position.