Dual-sided lithography: a method for evaluating alignment accuracy

We describe a method for measuring the accuracy of aligners used to align lithographic patterns on opposite sides of a substrate (back-to-front aligners). The method, with minor modifications, can also be used as an aid in performing back-to-front alignments. The method is based on interferometric principles, is insensitive to manufacturing errors, and is simple to implement. The version described in this paper is fabricated by using binary optics technology and can measure the accuracy of aligners to +/-0.2 microm.