Optical inspection of periodic structures using lens arrays and moire magnification

Abstract

This paper describes a technique that uses the phenomenon of moire magnification, developed recently for the measurement and inspection of periodic structures. Moire magnification occurs when an array of lenses is used to view an array of identical objects situated at the focal plane of the lenses. As the lens array is aligned with the object array, a moire pattern is observed in which each moire fringe consists of a magnified image of the repeat element of the object array. As the arrays are rotated with respect to each other, the magnification and orientation of the image changes.

The moire magnifier builds up an image from a large number of components of an array and therefore gives a representation of the average unit. It is a very simple and robust device and may well be more convenient to use, for example in an industrial production environment, than a microscope. A large number of components used in electronic imaging systems are periodic in nature and can conveniently be inspected using this technique. Examples are shown.

Key Words:

• Moire magnification
• Periodic structures
• Lens arrays