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.