<title>Scanning Moire interferometry</title>

Abstract

3D measurements of industrial surfaces is increasingly needed to meet today's quality control requirements, especially in the semiconductor industry. Camera based moire interferometry systems employing phase shifting analysis offer high resolution, but have not commonly been used because of limited data acquisition rates. This paper presents a technique called Scanning Moire Interferometry (SMI^TM) which provides the advantage of high resolution offered by phase shifting analysis while acquiring data at megaHertz rates. The technique is based on the use of a tri- linear CCD sensor. The moire light pattern projector is fixed in position with respect to the tri-linear sensor versus traditional techniques which shift the pattern projector with respect to the sensor between image acquisitions. The SMI^TM technique continuously moves the target with respect to the sensor/projector pair. In this configuration the tri-linear sensor acquires three images, each of which represent a difference phase shift of the projected line pattern. Traditional phase measurement techniques are used to derive a height map of the target from the three phase shifted images. A sensitivity analysis and height measurements of a ball grid array semiconductor package are presented. The advantages of the SMI^TM technique are high resolution, high speed and no moving parts in the sensor assembly.