Calibration of test masks used for lithography lens systems

The ongoing shrinkage of critical dimensions tremendously tightens the requirements on all important components within the semiconductor production chain. One of the most critical process steps in IC-production is lithography using advanced wafer scanners with its integrated projection lens system. The quality of the optical imaging process by means of the projection lens system is crucial to the production yield and quality of patterned wafers. For characterization of some of the important optical parameters of the projection lens system special test masks are used. We report on the calibration approach and results as well as the application of the test masks for the qualification process of the projection lens systems and we will concentrate here on two different sets of test masks. One test mask set consists of a larger number of finger-type grating structures in different orientations and with a nominal CD between 65 nm and 130 nm in wafer dimensions while the other set of qualification masks consists of two different masks with one-dimensional gratings of nominally 1:4 grating pitch ratio.