NEW ALIGNMENT SENSORS FOR OPTICAL LITHOGRAPHY

Two alignment sensors, which will be used in half-micron and sub-half-micron lithography, have been newly developed and tested. Both were developed to improve overlay accuracy on some particular types of processed layers with which the current alignment system has problems. One has an incoherent illumination and bright field imaging system with the aim being to reduce scaling and random errors on Al layers. The other is an optical heterodyne sensor of which the aims are to reduce random errors on Al layers and increse the signal detecting capability for small step height marks. These sensors proved to be effective on most difficult layers, and they have practical throughput.