Systematic investigation of CD metrology tool response to sidewall profile variation on a COG test mask

Different type of CD metrology instrumentation is in use today for production control of photomasks, namely SEM, AFM as well as optical microscopy and optical scatterometry is emerging, too. One of the challenges in CD metrology is to develop a system of cross calibration which allows a meaningful comparison of the measurement results of the different systems operated within a production environment. Here it is of special importance to understand and also to be able to simulate the response of different metrology instrumentation to variations in sidewall profile of features on photomasks. We will report on the preparation of a special COG test mask with an intended variation of sidewall features and the subsequent metrological characterization of this mask in different type of CD instrumentation. The discussion of the measurement results will be accompanied by a discussion of the simulation of instrument response to feature sidewall variation.