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Articles you may be interested inAccurate noncontact calibration of colloidal probe sensitivities in atomic force microscopy Rev. Sci. Instrum. 80, 065107 (2009); 10.1063/1.3152335 SI traceable calibration of an instrumented indentation sensor spring constant using electrostatic force Rev. Sci. Instrum. 79, 095105 (2008); 10.1063/1.2987695Silicon nanowires with sub 10 nm lateral dimensions: From atomic force microscope lithography based fabrication to electrical measurements The use of critical dimension atomic force microscopes ͑CD AFMs͒ in semiconductor manufacturing, both for process control and as a reference metrology tool, is increasing. If the tip width is calibrated consistently between measurements, a CD AFM can function as an excellent width comparator. Relative widths can be measured with uncertainties of 1 nm or less. However, to perform accurate measurements, the absolute tip width must be accurately calibrated. Until recently, conventional methods for accomplishing this had standard uncertainties on the order of 5 nm. Recently developed CD reference materials now make it possible to calibrate absolute tip width with uncertainties at the 1 nm level. The highlights of our method are: ͑1͒ the use of single-crystal silicon and preferential etching to pattern well-defined and highly uniform features; ͑2͒ the use of high resolution transmission electron microscopy ͑HRTEM͒ to access the Si lattice spacing directly as a source of traceable width information, and ͑3͒ the use of CD AFM to transfer width information from the HRTEM samples. These standards are known as single crystal critical dimension reference materials ͑SCCDRM͒, and prototype SCCDRMs have recently been delivered to SEMATECH Member Companies for evaluation.

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In critical dimension atomic force microscopy (CD-AFM), a major source of uncertainty is due to the tip. Measurements made using a CD-AFM tip show an apparent broadening of the feature width. Usually, the linewidth can be approximately corrected if the tip width is known. In addition to tip width broadening, tip-shape-dependent effects—also known as higher order tip effects—are a contributor to the uncertainty of CD-AFM linewidth measurements. These are especially important for undercut features and samples with relatively large sidewall roughness. In this paper, we examine the different types of CD-AFM higher order tip effects within the context of a reference measurement system and present a procedure for estimating some of these contributions with an uncertainty of less than 1.5 nm.

The National Institute of Standards and Technology (NIST) and SEMATECH have been working together to improve the traceability of critical dimension atomic force microscope (CD-AFM) dimensional metrology in semiconductor manufacturing. A major component of this collaboration has been the implementation of a Reference Measurement System (RMS) at SEMATECH using a current generation CD-AFM. An earlier tool, originally used at SEMATECH, has now been installed at NIST. Uncertainty budgets were developed for pitch, height, and CD measurements using both tools. At present, the standard uncertainties are approximately 0.2 % for pitch measurements and 0.4 % for step height measurements. Prior to the current work, CD-AFM linewidth measurements were limited to a standard uncertainty of about 5 nm. However, this limit can now be significantly reduced. This reduction results from the completion of the NIST/SEMATECH collaboration on the development of single crystal critical dimension reference materials (SCDDRM). A new generation of these reference materials was released to SEMATECH Member Companies during late 2004. The SEMATECH RMS was used to measure the linewidths of selected features on the distributed specimens. To reduce the uncertainty in tip width calibration, a separate transfer experiment was performed in which samples were measured by CD-AFM and then sent for high resolution transmission electron microscopy (HRTEM). In this manner, CD-AFM could be used to transfer the HRTEM width information to the distributed samples. Consequently, we are now able to reduce the limit on the standard uncertainty (k = 1) of CD-AFM width measurements to 1 nm.

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We experimentally demonstrate that the three-dimensional (3-D) shape variations of nanometer-scale objects can be resolved and measured with sub-nanometer scale sensitivity using conventional optical microscopes by analyzing 4-D optical data using the through-focus scanning optical microscopy (TSOM) method. These initial results show that TSOM-determined cross-sectional (3-D) shape differences of 30 nm–40 nm wide lines agree well with critical-dimension atomic force microscope measurements. The TSOM method showed a linewidth uncertainty of 1.22 nm (k = 2). Complex optical simulations are not needed for analysis using the TSOM method, making the process simple, economical, fast, and ideally suited for high volume nanomanufacturing process monitoring.

Scanning probe microscope (SPM) dimensional metrology efforts at the US National Institute of Standards and Technology (NIST) are reviewed in this paper. The main SPM instruments for realizing the International System of Units (SI) are the Molecular Measuring Machine, the calibrated atomic force microscope and the critical dimension atomic force microscope. These are optimized for long-distance measurements, three-dimensional measurements over conventional SPM distances and critical dimension or linewidth measurements, respectively. 10 mm distances have been measured with the relative standard uncertainty, uc, of 1.5 × 10−5; step heights at the 100 nm scale have been measured with the relative uc of 2.5 × 10−3 and sub-micrometer linewidths have been measured with uc = 0.8 nm.