Alignment system for optical lithography

An alignment system for locating a position of a reversible work piece, comprising:

• one or more stage cameras situated to view first and second sites on a first side of the work piece through a stage so as to obtain microscopic grain images of the work piece at the respective first and second sites;
• an area camera situated to view approximate locations of the respective first and second sites on the first side of the work piece when the work piece is reversed so as to obtain microscopic grain images at the respective approximate locations of the first and second sites;
• and
• a computer adapted to determine a position of a reversed work piece viewed by the area camera relative to the first and second sites viewed by the one or more stage cameras by performing a pattern match of the microscopic grain images of the work piece surface obtained by the area camera and by the one or more stage cameras.

A method of optically aligning a substrate, comprising:

• establishing an original coarse position of a substrate;
• creating original microscopic grain images with one or more first cameras aimed at multiple regions of the substrate;
• establishing a new coarse position of the substrate after repositioning the substrate and obtaining new microscopic grain images of the multiple regions;
• and
• performing pattern comparison of the original and new images of the respective regions until a pattern match is recognized, the images recording unique microscopic non-uniformities inherent to the substrate, thereby finely locating the position of the repositioned substrate.

A method of aligning a reversible work piece, comprising:

• placing the work piece in an obverse position onto a stage;
• viewing and storing microscopic grain images of first and second sites of a first side of the work piece through the stage by one or more stage cameras;
• reversing the work piece on the stage;
• viewing and storing microscopic grain images of at approximate locations of the first and second sites by an area camera;
• computing a relative position of the reversed work piece by performing a pattern match of the images obtained by the area camera with the images obtained by the one or more stage cameras.