182 IEEE TRANSACTIONS ON SEMICONDUCTOR MANUFACTURING, VOL. 11, NO. 2, MAY 1998 Electrical Linewidth Test Structures Fabricated in Monocrystalline Films for Reference-Material Applications Michael W. Cresswell, Senior Member, IEEE, Richard A. Allen, Member, IEEE, William F. Guthrie, Jeffry J. Sniegowski, Rathindra N. Ghoshtagore, Senior Member, IEEE, and Loren W. Linholm, Fellow, IEEE Abstract— The physical widths of reference features incorpo- rated into electrical linewidth test structures patterned in films of monocrystalline silicon have been determined from Kelvin voltage measurements. The films in which the test structures are pat- terned are electrically insulated from the bulk-silicon substrate by a layer of silicon dioxide provided by SIMOX (Separation by the IMplantation of OXygen) processing. The motivation is to facilitate the development of linewidth reference materials for critical-dimension (CD) metrology-instrument calibration. The selection of the (110) orientation of the starting silicon and the orientation of the structures’ features relative to the crystal lattice enable a lattice-plane-selective etch to generate reference- feature properties of rectangular cross section and atomically planar sidewalls. These properties are highly desirable for CD applications in which feature widths are certified with nanometer- level uncertainty for use by a diverse range of CD instruments. End applications include the development and calibration of new generations of CD instruments directed at controlling processes for manufacturing devices having sub-quarter-micrometer fea- tures. I. INTRODUCTION T HE END GOAL of the development of the test structures described here is to take advantage of the low cost and exceptional repeatability of electrical CD-metrology for the purpose of certifying CD-reference materials to support sub-quarter-micrometer metrology for advanced lithography- process control. A. Benefits of Electrical Test Structures for Linewidth Metrology A distinguishing characteristic of electrical linewidth mea- surements is their high level of repeatability. For a line Manuscript received October 14, 1997; revised January 15, 1998. This work was supported by the Sandia Corporation, a Lockheed-Martin Company, for the United States Department of Energy under Contract DE-AC04- 94AL85000. The Sandia effort was specifically supported through the Sandia/SEMATECH Cooperative Research and Development Agreement (CRADA Number 1082). Support was also provided by the National Semiconductor Metrology Program at the National Institute of Standards and Technology. M. W. Cresswell, R. A. Allen, R. N. Ghoshtagore, and L. W. Linholm are with the Semiconductor Electronics Division, National Institute of Standards and Technology, Gaithersburg, MD 20899 USA (e-mail: michael.cresswell@nist.gov). W. F. Guthrie is with the Statistical Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD 20899 USA. J. J. Sniegowski is with the Microelectronic Development Laboratories Sandia National Laboratories, Albuquerque, NM 87185 USA. Publisher Item Identifier S 0894-6507(98)02930-3. of conducting material having a nominal dimension of 1 m for example, we have observed that the repeatability of the measurement of the electrical linewidth is better than 1 nm This exceeds the performance of any other CD-metrology technique by a factor of about five. Other important benefits include the modest instrumentation cost and a nonvacuum substrate-inspection medium. B. Electrical CD Metrology for Certification of Linewidth-Reference Materials A well-known limitation of electrical CD metrology is that it is applicable in only those cases where the inspected features are electrically conducting. This is the reason that other techniques, in particular scanning electron microscopy, are used in semiconductor production for the measurement of features replicated in photoresist. However, the calibration support of such instruments is very demanding and, at the present time, artifacts having widths below 0.5 m are not available. The electrical CD-metrology innovations reported here aim at developing a new class of CD-reference artifacts for the purpose of supporting the design and calibration of instruments, including those based on nonelectrical techniques, which are likely to continue to be used in resist-patterning applications in sub-quarter-micrometer device fabrication. II. REQUIREMENTS FOR LINEWIDTH REFERENCE-MATERIAL CERTIFICATION When a reference artifact is used to develop or calibrate an instrument for the measurement of a property, such as feature CD, measurements extracted from the artifact should not exhibit instrument-type-dependent differences. If, for example, respective sets of measurements of feature linewidths made on CD artifacts by a selection of atomic force microscopes, and by a selection of scanning-beam systems, are systematically different, then the metrology is said to exhibit methods diver- gence. This difference can sometimes amount to a significant fraction of the nominal linewidth [1]. The prevalence of this condition challenges reference-material certification. A. Sources of Methods Divergence One source of methods divergence is the difference of the responses of respective instrument types to different physical U.S. Government work not protected by U.S. copyright