Development of an algorithm for monitoring of pattern fidelity on photomasks for 0.2μm technology and beyond based on light optical CD metrology tools

With the ongoing shrinking of design rules, the complexity of photomasks does increase continuously. Features are getting smaller and denser, their characterization requires sophisticated procedures. Looking for the deviation from their target value (CD-offtarget) and their linewidth variation (CD-uniformity) is not sufficient any more. In addition, measurements of corner rounding and line end shortening are necessary to define the pattern fidelity on the mask. Otherwise printing results will not be satisfying. Contacts and small features are suffering mainly from imaging inaccuracies. The size of the contacts as an example may come out too small on the photomask and therefore reduces the process window in lithography. In order to meet customer requirements for pattern fidelity, a measurement algorithm and a measurement procedure (e.g. implementing of test patterns on critical layers) needs to be introduced and specifications to be defined. In this paper different approaches are compared, allowing an automatic qualification of photomasks by optical light microscopy based on a MueTec CD-metrology system, the newly developed MueTec 2030UV, provided with a 365 nm light source (i-line). The i-line illumination allows to resolve features down to 0.2 mu m size with good repeatability.