Test structures for CD and overlay metrology on alternating aperture phase-shifting masks

The ability to test and characterise advanced photomasks for verification and process control is increasingly important and this paper builds on previous work in this area. Atomic force and scanning electron microscope measurements are used to explain anomalies in previously presented results. In addition, a new test structure has been developed to measure an important parameter in alternating aperture phase shifting masks: the alignment between the chrome blocking features and the phase shifting regions etched into the quartz substrate. Simulation results are presented which demonstrate the capability of the test structure when used in a progressional offset array.