Mapping the Edge Roughness of Test-Structure Features for Nanometer-Level CD Reference-Materials ¶ M.W. Cresswell, M. Davidson, 1 G.I. Mijares, R.A. Allen, J. Geist, M. Bishop 2 Semiconductor Electronics Division, Electronics and Electrical Engineering Laboratory National Institute of Standards and Technology, Gaithersburg, Maryland, USA 1 Spectel Research Corp., Palo Alto, California, USA 2 International SEMATECH, Montopolis Drive, Austin, Texas, USA. ABSTRACT The near-term objective of the work reported here is to develop a protocol for rapidly mapping critical-dimension (CD) and edge roughness from high-resolution Scanning- Electron Microscopy (SEM) images of reference-material features patterned on Single-Crystal CD Reference Material (SCCDRM) chips. The longer term mission is to formulate a metric to enable automated characterization of as-fabricated reference-feature segments for rapid identification of fabrication-process enhancements and, ultimately, to select feature segments for further characterization as standard reference- materials. The selection of results presented here provides a new level of SCCDRM characterization showing that segments of some SCCDRM features appear to have very useful extended lengths of up to 200 nm of superior CD uniformity. BACKGROUND † Fabrication processes and calibration procedures for making silicon-based prototype critical-dimension (CD) reference features available to industry have been under development in a multi-laboratory National Institute of Standards and Technology (NIST) project for several years. 1 The silicon technology is known as the Single- Crystal CD Reference Material (SCCDRM) implementation. The end application for these reference materials is metrology support for sub 100 nm gate- length IC fabrication. The project has so far delivered a selection of reference materials for evaluation to the International SEMATECH Manufacturing Initiative and other organizations. 2 The better SCCDRM calibrated reference features with sub-tenth-micrometer linewidths that have so far been delivered have expanded uncertainties as low as 1.25 nm. ‡ Navigation errors sustained during calibration team up with residual reference-feature CD non-uniformity to generate † ¶ Contribution of the National Institute of Standards and Technology (NIST). Not subject to copyright. ‡ For a description of terminology see, for example, http://physics.nist.gov/cuu/Uncertainty/coverage.html . contributions of approximately 25 % of this amount. However, calibration with sub-single-nanometer uncertainty is understood to be highly desirable for end- user applications. The fact is that the significant uncertainty contribution above could be driven towards zero if a way could be found to fabricate reference features with CD roughness consistent with atomic-level feature-sidewall planarity along segment lengths as long as 0.25 μm, for example. Until very recently, the longest feature segments having this property extended for approximately 50 nm. However, further fabrication- process enhancement to generate greater lengths of quasi- atomic-sidewall-planarity is challenged by the possible existence of spatially random local regions of anomalous properties of the starting-material extending to over hundreds of nanometers. The approach that has been adopted here to minimize the adverse impact of these properties, and to produce 250 nm feature-segments having near-zero edge roughness, is to devise appropriate fabrication processing with the aid of a high-throughput data-acquisition protocol to identify regions of processing space that minimize, or zero, intra-feature CD and edge roughness. Simultaneously, the same data acquisition identifies the locations of segments on a feature having superior edge and CD roughness. The specific technical approach, namely automated dimensional analysis of high-resolution Scanning-Electron Microscopy (SEM) images, has been applied to a selection of SCCDRM features having CDs in the range 50 nm to 200 nm. The results provide an essential assessment of the current baseline SCCDRM fabrication process vis-à-vis CD- uniformity and edge roughness. This is a prerequisite to the next step of formulating a metric to enable automated identification and ranking of as-fabricated reference- feature segments to be used to support fabrication-process enhancements and, ultimately, to select features for further qualifying metrology for standard reference- material applications. 3 One of many recent articles exemplifies how topical the issue of edge-roughness metrology has become. 4 However, there appear to be no prior reports on the unique and specific application that is the subject of this paper. Alternative methods include, for example,