Nanometer-scale dimensional metrology for advanced lithography

Abstract
Increased performance of lithographic process techniques has been the key enabler for the continued reduction of minimum device feature sizes down to 0.25 μm and beyond. However, this increase in performance has been accompanied by the added fabrication complexity of the various types of lithographic reticles. Theoretical simulations have revealed that metrological requirements for the fabrication of devices having subhalf micrometer dimensions are indeed on the nanometer scale. A comparison of available metrology tools is presented as well as improvements to current techniques. Direct correlations between top-down critical dimension cleanroom scanning electron microscopy (SEM), cross-sectional analytical SEM, and various atomic force microscopy (AFM) techniques (scanning techniques and probe shapes) are described as well as the use of AFM to nondestructively characterize features on x-ray membrane masks is described. Finally, the use of novel optical fiber probes to image subresolution quartz features on optical phase-shifting masks is presented.

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