Improved test structures for the electrical measurement of feature size on an alternating aperture phase-shifting mask

Electrical test structures have been designed that are compatible with a standard alternating aperture, phase-shift mask manufacturing process. Measurements indicate that these have superior performance to previous designs where Greek cross structures suffered from asymmetry problems. As a result, the new test structures extract a consistent, and accurate, sheet resistance. In addition, the measurements on linewidth structures have demonstrated an improved capability with the CD offset variability being reduced to a quarter of the previous value. Electrical CD results from a wide range of test structures, both phase-shifted and binary, are presented and it is demonstrated that the phase-shifting elements have a negligible effect on the measurements. A limited number of atomic force microscope measurements have also been made for comparison purposes

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