William F. Guthrie

Nanoindentation of polymers : An overview

In this paper, the application of instrumented indentation devices to the measurement of the elastic modulus of polymeric materials is reviewed. This review includes a summary of traditional analyses of load-penetration data and a discussion of associated uncertainties. Also, the use of scanning probe microscopes to measure the nanoscale mechanical response of polymers is discussed, particularly with regard to the associated limitations. The application of these methods to polymers often leads to measurements of elastic modulus that are somewhat high relative to bulk measurements with potentially artificial trends in modulus as a function of penetration depth. Also, power law fits to indentation unloading curves are often a poor representation of the actual data, and the power law exponents tend to fall outside the theoretical range. These problems are likely caused by viscoelasticity, the effects of which have only been studied recently. Advancement of nanoindentation testing toward quantitative characterization of polymer properties will require materialindependent calibration procedures, polymer reference materials, advances in instrumentation, and new testing and analysis procedures that account for viscoelastic and viscoplastic polymer behavior.

An Approach to Combining Results From Multiple Methods Motivated by the ISO GUM.

The problem of determining a consensus value and its uncertainty from the results of multiple methods or laboratories is discussed. Desirable criteria of a solution are presented. A solution motivated by the ISO Guide to the Expression of Uncertainty in Measurement (ISO GUM) is introduced and applied in a detailed worked example. A Bayesian hierarchical model motivated by the proposed solution is presented and compared to the solution.

Traceable Calibration of Critical-Dimension Atomic Force Microscope Linewidth Measurements with Nanometer Uncertainty

The use of critical dimension atomic force microscopes (CD AFMs) 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: (1) the use of single-crystal silicon and preferential etching to pattern well-defined and highly uniform features; (2) the use of high resolution transmission electron microscopy (HRTEM) to access the Si lattice spacing directly as a source of traceable width information, and (3) the...

Development of a Standard Reference Material for Metabolomics Research

The National Institute of Standards and Technology (NIST), in collaboration with the National Institutes of Health (NIH), has developed a Standard Reference Material (SRM) to support technology development in metabolomics research. SRM 1950 Metabolites in Human Plasma is intended to have metabolite concentrations that are representative of those found in adult human plasma. The plasma used in the preparation of SRM 1950 was collected from both male and female donors, and donor ethnicity targets were selected based upon the ethnic makeup of the U.S. population. Metabolomics research is diverse in terms of both instrumentation and scientific goals. This SRM was designed to apply broadly to the field, not toward specific applications. Therefore, concentrations of approximately 100 analytes, including amino acids, fatty acids, trace elements, vitamins, hormones, selenoproteins, clinical markers, and perfluorinated compounds (PFCs), were determined. Value assignment measurements were performed by NIST and the Centers for Disease Control and Prevention (CDC). SRM 1950 is the first reference material developed specifically for metabolomics research.

RM 8111: Development of a Prototype Linewidth Standard.

Staffs of the Semiconductor Electronics Division, the Information Technology Laboratory, and the Precision Engineering Laboratory at NIST, have developed a new generation of prototype Single-Crystal CD (Critical Dimension) Reference (SCCDRM) Materials with the designation RM 8111. Their intended use is calibrating metrology instruments that are used in semiconductor manufacturing. Each reference material is configured as a 10 mm × 11 mm silicon test-structure chip that is mounted in a 200 mm silicon carrier wafer. The fabrication of both the chip and the carrier wafer uses the type of lattice-plane-selective etching that is commonly employed in the fabrication of micro electro-mechanical systems devices. The certified CDs of the reference features are determined from Atomic Force Microscope (AFM) measurements that are referenced to high-resolution transmission-electron microscopy images that reveal the cross-section counts of lattice planes having a pitch whose value is traceable to the SI meter.

CD-AFM reference metrology at NIST and SEMATECH

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.

Recent Developments in Electrical Linewidth and Overlay Metrology for Integrated Circuit Fabrication Processes

Electrical linewidth measurements have been extracted from test structures replicated in planar films of monocrystalline silicon that were electrically insulated from the bulk-silicon substrate by a layer of silicon dioxide formed by separation by the implantation of oxygen (SIMOX) processing. Appropriate selection of the surface orientation of the starting material, the design and orientation of the structures features, and patterning by a lattice-plane selective etch provide features with planar, atomically smooth sidewalls and rectangular cross sections. The primary motivation for this approach is to attempt to overcome the serious challenge posed by methods divergence to the certification of linewidth reference-materials for critical-dimension (CD) instrument calibration and related tasks. To enhance the physical robustness of reference features with deep submicrometer linewidths, the new test structure embodies short reference-segment lengths and arbitrarily wide voltage taps. Facilities for reconciliation of measurements extracted from the same feature by all normally practiced techniques are also implemented. In overlay metrology, electrical inspection of two types of hybrid overlay targets allows pixel calibration of, and shift extraction from, the overlay instruments. The overall strategic focus of this research is to resolve methods-divergence issues and possibly to develop universal deep-submicrometer linewidth reference materials for CD instruments and techniques for instrument- and process-specific shift extraction for optical overlay metrology.

Traceable atomic force microscope dimensional metrology at NIST

The National Institute of Standards and Technology (NIST) has a multifaceted program in atomic force microscope (AFM) dimensional metrology. There are two major instruments being used for traceable AFM measurements at NIST. The first is a custom in-house metrology AFM, called the calibrated AFM (C-AFM), and the second instrument is a commercial critical dimension AFM (CD-AFM). The C-AFM has displacement metrology for all three axes traceable to the 633 nm wavelength of the Iodine-stabilized He-Ne laser. In the current generation of this system, the relative standard uncertainty of pitch and step height measurements is approximately 1.0 x 10-3 for pitches at the micrometer scale and step heights at the 100 nm scale, as supported by several international comparisons. We expect to surpass this performance level soon. Since the CD-AFM has the capability of measuring vertical sidewalls, it complements the C-AFM. Although it does not have intrinsic traceability, it can be calibrated using standards measured on other instruments - such as the C-AFM, and we have developed uncertainty budgets for pitch, height, and linewidth measurements using this instrument. We use the CD-AFM primarily for linewidth measurements of near-vertical structures. At present, the relative standard uncertainties are approximately 0.2% for pitch measurements and 0.4% for step height measurements. As a result of the NIST single crystal critical dimension reference material (SCCDRM) project, it is possible to calibrate CD-AFM tip width with a 1 nm standard uncertainty. We are now using the CD-AFM to support the next generation of the SCCDRM project. In prototypes, we have observed features with widths as low as 20 nm and having uniformity at the 1 nm level.

Test structures for referencing electrical linewidth measurements to silicon lattice parameters using HRTEM

A technique has been developed to determine the linewidths of the features of a prototype reference material for the calibration of critical-dimension (CD) metrology instruments. The reference features are fabricated in mono-crystalline-silicon with the sidewalls aligned to the (111) lattice planes. A two-step measurement procedure is used to determine the CDs. The primary measurement is via lattice-plane counting of selected samples using high-resolution transmission electron microscopy (HRTEM); the transfer calibration is via electrical CD (ECD) test-structure metrology. Samples of these prototype reference materials were measured and provided, as the National Institute of Standards and Technology (NIST) Reference Material RM8110, to International SEMATECH for evaluation by its member companies. In this paper, we will describe the measurement procedure and show how the combined uncertainty of less than 15 nm was derived. Additionally, we demonstrate a technique to automate the analysis of the phase-contrast images in order to both minimize the cost and reduce the uncertainty of the calibration of the standards.

Gravimetric approach to the standard addition method in instrumental analysis. 1.

A mathematical formulation for a gravimetric approach to the univariate standard addition method (SAM) is presented that has general applicability for both liquids and solids. Using gravimetry rather than volumetry reduces the preparation time, increases design flexibility, and makes increased accuracy possible. SAM has most often been used with analytes in aqueous solutions that are aspirated into flames or plasmas and determined by absorption, emission, or mass spectrometric techniques. The formulation presented here shows that the method can also be applied to complex matrixes, such as distillate and residual fuel oils, using techniques such as X-ray fluorescence (XRF) or combustion combined with atomic fluorescence or absorption. These techniques, which can be subject to matrix-induced interferences, could realize the same benefits that have been demonstrated for dilute aqueous solutions.