System for Measuring Three-Dimensional Micro-Structure Based on Phase Shifting Fringe Projection

Abstract

We have developed a telecentric three dimensional measurement system based on fringe projection techniques to measure the absolute phase corresponding to the three dimensional shape of micro structure profile, like micro bumps, pillars and solder bumps etc. Fringe projecting module with adjustable fringe density and projecting angles are designed to flexibly and accurately introduce the phase shifting algorithm. In tradition, all of the fringe projection techniques are used by two ways, which one is the tri-linear camera obtained three of fringe images by the separate line camera, and the other one is the three fringes image taken and processed through area camera one by one to measure three dimensional profiles. The advantage of the former can provide for high speed scanning phase measuring of an object, but it can't measure mirror like sample, like wafer bumps, because of the hardware limited. And the latter can measure mirror like sample but the technology need to be changed the phase module of the light source lead to the measurement speed to be slow. In this paper, we use the area camera to acquire three of fringe images with 120° phase shifting simultaneously by the pixels in each rows without changing the phase module of the light source are sufficient to reconstruct a 3D model. By using this technique, we can further improve the measuring speed of the structure light system, and the system will be more resistant to fast moving objects. The measurement accuracy for the height of the micro bumps range of $5-2000\ \mu\mathrm{m}$ is verified as less than $1\ \mu\mathrm{m}$.