Overlay Distortion Evaluation of Projection Printers
Original Publication Date: 1984-Mar-01
Included in the Prior Art Database: 2005-Feb-03
A simple and fast technique for the evaluation of the distortion and magnification error in a projection printer is disclosed. As the dimensions of integrated circuit features decrease in size, the accurate alignment and printing of overlay images into photoresist in sequential mask steps becomes critical. The distortions inherent in any optical projection system used to print an image will, however, change with time and thus must be continually monitored and corrected for. The distortion including magnification errors, for a particular projection system, are monitored by superimposing developed mask patterns in an oxide layer on a silicon wafer from a standard machine and the machine under test.