MARK DETECTION FOR ALIGNMENT AND REGISTRATION IN A HIGH-THROUGHPUT PROJECTION ELECTRON LITHOGRAPHY TOOL

The design considerations and performance requirements of an alignment and registration method for high-throughput projection electron lithography are discussed. We have devised a mark detection system for a lithography tool employing the SCALPEL principle. The process involves scanning the image of a mark from a mask, over a mark that is fabricated on a wafer and measuring the integrated backscattered-electron intensity. Using a mark that consists of equally spaced lines of tungsten on silicon, we have investigated the effects of spatial and rotational misalignment, and focus in a small field of view SCALPEL machine. We have modeled these and other effects and found agreement between experimental and theoretical results. The measured precision of estimating position from the experimental data is approximately 10 nm. By extrapolation we believe that in a practical lithography machine this value can be improved significantly.