Sub-100 nm metrology using interferometrically produced fiducials

Pattern-placement metrology plays a critical role in nanofabrication. Not f ar in the future, metrology standards approaching 0.2 nm in accuracy will b e required to facilitate the production of 25 nm semiconductor devices. The y will also be needed to support the manufacturing of high-density waveleng th-division-multiplexed integrated optoelectronic devices. We are developin g anew approach to metrology in the sub-100 nm domain that is based on usin g phase-coherent fiducial gratings and grids patterned by interference lith ography. This approach is complementary to the traditional mark-detection, or "market plot" pattern-placement metrology. In this article we explore th e limitations of laser-interferometer-based mark-detection metrology, and c ontrast this with ways that fiducial grids could be used to solve a variety of metrology problems. These include measuring process-induced distortions in substrates; measuring patterning distortions in pattern-mastering syste ms, such as laser and e-beam writers; arid measuring field distortions and alignment errors in steppers and scanners. We describe a proposed standard for pattern-placement metrology, which includes both a fiducial grid and ma rket-type marks; Finally, a number of methods through which phase-coherent periodic structures can be patterned are shown, including "traditional" int erference lithography, achromatic interference lithography, near-field inte rference lithography, and scanning-beam interference lithography. (C) 1999 American Vacuum Society. [S0734-211X(99)11806-7].