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Process Measurements Flow Measurement Research and Standards Thermophysical Properties of Gases Thermophysical Properties of Semiconductor Processing Gases Measurement Technology for Benchmark Spray Combustion Data Flow and Chemistry in Thermal Reactors Standards for Raman Spectroscopy Plasma Processing of Semiconductors Solid-State Chemical Microsensors High-Temperature Thermocouples Pressure, Vacuum, and Low-Flow Standards Quantitative Optical Measurements of Partial Pressures and Moisture |
Division Contact: James Whetstone Flow Measurement Research and Standards The accelerating costs of scarce fluid resources and valuable fluid products-particularly petrochemical fluids-are causing increased concerns about the performance of flow meters. Additionally, the role of flow meters in controlling and optimizing critical industrial processes is pushing performance limits and extending the required fluid and flow conditions. To attain these goals, improved flow traceability to NIST standards is essential. Improved flow measurement traceability needs to be established and maintained so that realistic, quantified data are generated on a continuing basis to ensure practical fluid measurements at satisfactory performance. To achieve the desired flow measurement traceability, we are conducting several flow measurement proficiency testing programs for a range of fluid and flow conditions. We also are designing new transfer standards to link the performance of calibration facilities having special conditions and capabilities to appropriate national reference standards. Because of the importance
of critical flow measurements, transfer standards need to be designed
and used so that high levels of confidence can be placed in the measurements
from critical flow meters. We rigorously evaluate new transfer standards
against NIST fluid flow calibration standards. As part of these evaluations,
we will perform the appropriate range of calibrations on the developed
standards so performance can be ensured at specified levels. Our current
fluid metering research programs use computational fluid dynamics to focus
on flows that are critical to U.S. industry. Currently, we are researching
assessment of acoustic technology for making improved flow measurements
and the description of flow meter installation effects. Contact: Pedro I. Espina Thermophysical Properties of Gases Thermophysical properties of gases are required to design heat transfer machinery and chemical processes. We obtain very accurate values for these properties (equation of state, heat capacity, thermal conductivity, viscosity, and speed of sound) by exploiting high-Q acoustic resonators that we have developed and modeled. We routinely measure the speed of sound in gases with uncertainties of less than ±0.01 percent. We used our data to determine the thermodynamic properties of more than 20 environmentally benign, candidate replacement refrigerants and of helium-xenon mixtures used in thermoacoustic refrigerators. To extend these measurements to corrosive gases and gases at very high temperatures, we developed acoustic wave guides to conduct sound from remote transducers into and out of resonators through corrosion-resistant metal diaphragms. We also developed novel acoustic resonators for measuring the viscosity and thermal conductivity of gases with an imprecision of 0.1 percent. We are using acoustic
measurements of the highest possible accuracy to measure the imperfections
in the internationally accepted temperature scale (ITS-90) in the range
200 kelvin to 700 kelvin. For this work, we measure the speed of sound
in argon with an imprecision of 0.0001 percent in a spherical resonator.
We measure the thermal expansion of the resonator using microwaves. To
maintain the purity of the argon at 700 kelvin, clean argon continuously
flows through the resonator with a pressure that is controlled to one
part in 106. Contact: Michael R. Moldover Thermophysical Properties of Semiconductor Processing Gases Mass flow controllers (MFCs) deliver process gases for plasma etching, chemical vapor deposition, and other processes used throughout the semiconductor industry. The operation of the most widely used kind of MFC depends upon heat transfer through the process gas. Thus, the sensitivity of these MFCs depends upon the thermophysical properties of the process gas, and each gas requires a different MFC calibration. However, many process gases (such as Cl2, HBr, BCl3, and WF6) are toxic, corrosive, and/or pyrophoric, making it impractical to calibrate directly all MFCs for all 50 or so process gases. An alternative to direct calibration is based upon flowing benign "surrogate" gases (such as N2, CF4, SF6, or C2F6) through the MFCs and scaling the MFCs' response to account for the differences between the thermophysical properties of the surrogate gas and those of the process gas. The relevant gas properties are density, heat capacity, thermal conductivity, and viscosity. NIST is exploiting its expertise in acoustic technologies to measure these properties for the highest priority process, carrier, and surrogate gases throughout the temperature and pressure ranges in which MFCs operate. As data are acquired, they are being tabulated at http://properties.nist.gov/semiprop. Contact: John Hurly Measurement Technology for Benchmark Spray Combustion Data Control of process efficiency and the formation of species byproducts from industrial thermal oxidation systems (e.g., power generation and treatment of process liquid chemical wastes) generally are based on a priori knowledge of the input stream global physical and chemical properties, desired stoichiometric conditions, and monitoring of a few major chemical species in the exhaust. Engineers rely increasingly on computational models and simulations that help provide relevant process information in a cost-effective manner to optimize performance of these systems. In general, there is a dearth of reliable data for specifying model initial/boundary conditions. There is also a need for experimental/numerical comparative analysis of conditions within the reactor. Reactor volume is the principal variable that requires a better knowledge base to enable optimization of chemical and thermal processes and control of particulate and gaseous emissions. There is a need to provide in-situ, real-time data on the characteristics of droplet field and flame structure and relationship with system operating conditions (e.g., desired stoichiometry), heat transfer, and particulate/gaseous byproducts. These data are crucial for the development and calibration of advanced computational models, diagnostics, instrumentation, and the efficient operation of high-temperature process systems. We are carrying out
experiments in a spray combustion testbed, with a movable-vane swirl burner
enclosed in a refractory chamber. The well-characterized and controlled
facility has evolved to handle different process liquid fuels and wastes,
atomizer designs, and combustor configurations. We are using a unique
array of intrusive probes, non-intrusive diagnostics, and flow visualization
techniques to obtain comprehensive data on spray combustion characteristics.
In our current research, we measure input fuel stream (fuel composition),
spray flame (droplet size, velocity, number density, and temperature),
and combustor exhaust (particulate size, volume fraction, and toxic gas
concentrations). We are developing measurement technology to provide benchmark
experimental data that completely characterize the facility for input/validation/calibration
of multiphase combustion models, calibration of instrument/sensors, and
development of advanced diagnostics. We will use these databases to establish
correlations between operating conditions and the resultant spray flame
characteristics, thermal gradients, and level of chemical byproducts in
combustion systems. Contact: Cary
Presser
Flow and Chemistry in Thermal Reactors Our program provides
measurements suitable for development and testing of models that may be
used as design tools for next-generation process equipment used in the
manufacture of microelectronic components. We focus on characterizing
both flow and chemistry in thermal reactors using a new optically accessible
rotating disk reactor. A major focus of this work is on the detection
of the early stages of contaminant particle formation. Additionally, we
will measure both chemical species and thermal fields under various operating
conditions. This work is in conjunction with a substantial modeling effort
in this type of reactor. Available facilities include excimer, neodymium-yttrium
aluminum garnet, and tunable dye laser systems; continuous-wave-ion lasers;
mass spectrometers; and high-performance graphics workstations. Our results
are expected to aid in the development of industrial process reactor simulations
and on-line diagnostics for process control as well as to increase fundamental
understanding of these important processes. Contact: James E. Maslar Standards for Raman Spectroscopy It is widely acknowledged that major advances in analytical Raman instrumentation have virtually revolutionized Raman spectroscopic measurements, and Raman spectroscopy now is finding its place in the industrial environment for process measurements and quality control. In Raman spectroscopy the intensity of the analytical signal is not calibrated as part of the measurement as in infrared spectroscopy. Consequently, relatively few published spectra have been corrected for the typical variations in the instrument response function, and there are no widely available standardized Raman spectral libraries. The lack of accepted practices, standards, and spectral libraries has been a main obstacle to the acceptance of Raman in industrial settings and is a barrier to its use in the regulated industries. Our research is concerned with critically evaluating existing approaches to the standardization of Raman measurements and aims to develop new methods and techniques so that calibration of Raman spectrometers can be reliably accomplished for both the signal intensity and for the Raman shift frequency. One approach will consist of the evaluation of the laser-excited fluorescence spectra of rare-earth doped glasses to provide broadband and narrow-band emissions over the common Raman spectral domains. These results will lead to the certification of a set of Standard Reference Materials® traceable to NIST primary radiometric standards. While fluorescence can be exploited for intensity calibration, a more fundamental approach will rest upon the determination of absolute Raman cross sections, which can provide an absolute intensity calibration that is verifiably instrument independent. Work is planned to
develop a Raman gain spectrometer for the measurement of the Raman cross
sections of judiciously chosen liquids and solids that may serve as absolute
Raman intensity standards. One thrust of the program is the close coordination
of this standards work with the objectives of various outside organizations
including the ASTM Committee for Raman Spectroscopy, which has adopted
a set of Raman standards initiatives. Close contacts are maintained with
the Raman community of major chemical industries and several regulatory
agencies. These liaisons are intended to provide opportunities for collaborative
work through appropriate cooperative agreements. Contact: Wilbur S. Hurst or Steven J. Choquette Plasma Processing of Semiconductors Plasmas are widely used by the semiconductor industry to etch and deposit films. Plasma processing reactors historically have been designed and operated using empirical methods alone, but continued evolution of these tools requires a much greater reliance on process and reactor modeling. Such models could be used as design tools for next-generation processes and equipment. Also, because most existing plasma diagnostic techniques are incompatible with the manufacturing environment, manufacturers need sensors for their environment, models to interpret the sensor readings, and new schemes of closed-loop control based on these sensors and models. The goal of our project is to develop advanced chemical and electrical measurement methods for characterizing plasmas, to use these measurements to test and develop models, and to apply the models to the development of new types of sensors and new design strategies. We make measurements of high-density and low-density plasmas in a standard plasma reactor known as the Gaseous Electronics Conference reference cell. Measurement techniques to probe gas and surface chemistry include optical emission, mass spectrometry, spectroscopic ellipsometry, absorption spectroscopy, and planar laser-induced fluorescence (PLIF). PLIF provides two-dimensional maps of gas phase species concentrations, enabling investigation of plasma spatial uniformity and rigorous testing of plasma simulations. Present PLIF studies focus on the fluorocarbon plasmas used for etching and chamber-cleaning. Electric probe and radio-frequency voltage and current waveform measurements provide electrical characterization of plasma parameters and reactor conditions. We use these electrical measurements, as well as ion energy measurements, to characterize and model plasma sheath dynamics. Sheath models developed and verified by this work have been used to optimize the efficiency of power utilization in chamber-cleaning plasmas and to develop a new technique for measuring the ion current at wafers during high-density plasma processing. Contact: Mark A. Sobolewski or Kristen L. Steffens Solid-State Chemical Microsensors The increasing demand for reliable chemical sensors is being driven by wide-ranging measurement needs. The chemical process industry, for example, now faces new demands for more efficient use of materials, better process reproducibility, and environmental safety. Similar concerns are encountered in the automotive field, where researchers are challenged to optimize engine performance while reducing emissions. To address such measurement needs, our program concentrates on developing generic sensor platforms, as well as fabrication and operational techniques, that allow sensors to be tuned-with active materials and temperature control-for detecting differing target gases and vapors within varied environments. Fundamental work on sensing materials is done to create the understanding necessary to optimize performance characteristics such as sensitivity, selectivity, speed, and stability. Microsensors are based on a "microhotplate" design developed and patented at NIST. These silicon-based, surface-micromachined devices, which have nominal lateral dimensions between 30 micrometers and 200 micrometers and masses of approximately 0.25 microgram, provide microplatforms with localized, measurable, and rapidly variable thermal control. The microhotplate structure can be repeated easily to form integrated arrays of multiple, individually addressable, and thermally isolated elements. Rapid heating (to 500 degrees Celsius and higher) and cooling characteristics of the devices allow dynamic temperature programming to be used in producing response signatures for identifying detected species. In this work, we use neural network methods with response training sets to develop heating schedules for high information content operation and recognition. Localized heating of the devices has been combined with chemical vapor deposition to directly define different active films on array elements. To date, most efforts have been connected to conductometric gas sensing with semiconducting oxide films (tin oxide, zinc oxide, and titanium oxide) that have been modified with catalytic metal additives (platinum and lead). However, we are developing modified versions of the microhotplate for sensing by calorimetric, capacitance, and other transduction principles. We now are examining the use of organic films, epitaxial films, and high-area metal dispersions for incorporation into the microsensor platforms. We are using thermally controlled array structures in efficient studies on materials suites for new applications and film processing methods that lead to optimized sensing performance. We are interested
in cooperative research that would assist in our efforts to understand
and advance sensing mechanisms, sensor materials, and sensing platforms.
Dedicated facilities for multitechnique surface analysis, device design
and micro-machining, and response testing can be utilized for investigating
new concepts and prototype structures, and for evaluating sensor performance
in specific application sectors. We also have a growing interest in algorithm
development for signal processing. Contact: Stephen Semancik or Richard E. Cavicchi Future sensors and diagnostics are being developed to perform multianalyte measurements rapidly, accurately, and at low cost. A promising approach is to use large-scale solid-phase arrays of DNA and proteins. For example, DNA chip technology has the potential for revolutionizing genetic diagnostic applications including disease detection, toxicology, forensics, industrial processing, and environmental monitoring. Although considerable effort is focused on applications of DNA and peptide arrays, relatively little research is directed toward understanding the molecular-scale structure and mechanisms that govern the surface reactions of these monolayer systems. To investigate many
of these issues, we are studying alkanethiol self-assembled monolayers
(SAMs) formed on gold substrates as a model system. SAMs are robust, reproducibly
prepared structures with highly tunable surface properties useful in sensing
applications. Currently, we are focusing on the structure/function properties
of thiol-derivatized, single-stranded DNA monolayers on gold and their
associated hybridization reactions. We are developing and applying optical
and electrochemical methods to these monolayers for in-situ determination
of surface DNA density, hybridization activity, and molecular orientation.
The goal of these studies is to ascertain the optimal film structure and
composition for promoting hybridization of surface-bound probes. Contact: Michael J. Tarlov High-Temperature Thermocouples High-temperature industrial processes along with scientific research at high temperatures are creating new requirements for stable thermometers that cover wider temperature ranges with better accuracy. Problems with thermocouples at high temperatures result primarily from unstable compositions (impurities, defects, and chemical reactions), causing their electromotive force, and thus their temperature indication, to drift with use and rapidly become highly uncertain. A second problem in process measurements is the unreliable measurement of surface temperatures resulting from the use of traditional contact and non-contact (radiation) thermometers. Accurate, high-speed measurements of temperatures of surfaces are especially critical in semiconductor wafer preparation by rapid thermal processing because accurate control of temperature during short high-temperature exposures is critical to product quality and device performance. We are developing
new wire and thin-film thermocouples as reference thermometers for secondary
calibration laboratories and as high-accuracy, high-stability, high-temperature
thermometers for industrial use, including use in surface-temperature
measurements. We are investigating noble metal thermocouples that are
of exceptionally high purity and generally resistant to oxidation at temperatures
as high as 1500 degrees Celsius. We also have successfully developed thin-film
thermocouples for accurate surface temperature measurements in semiconductor
processing applications. These devices become a part of the surface and
thereby minimize the uncertainties associated with conventional contact
thermometers (uncertainty of the correlation between measured temperature
and surface temperature) and with radiation thermometers (uncertainty
with respect to the time-dependent, effective emissivity of the surface). Contact: Dean Ripple Pressure, Vacuum, and Low-Flow Standards Many industries depend on accurate pressure, vacuum, and low-flow measurements for research and development and for process and quality control. We develop and maintain pressure and vacuum standards from 270 megapascals to 10-7 pascal; flow standards are operated from 10-3 moles per second to 10-14 moles per second. Facilities include five ultrahigh vacuum systems, three low-range and two mid-range flowmeters, high-accuracy mercury and oil manometers in both absolute and differential mode, oil and gas piston gauges, apparatuses for measuring gas densities using optical techniques, and the necessary pressure and vacuum control systems. These facilities are used to provide calibration support for industrial, academic, and government entities and for research to improve the fundamental understanding of physical phenomena or measurement capability. Measurement capabilities
at NIST enable researchers to develop improved measurement techniques
and equipment, and to investigate the performance of vacuum and pressure
instrumentation, specifically piston gauges, mechanical pressure gauges,
momentum transfer gauges, ionization gauges, microelectromechanical systems
(MEMS) sensors, thermal mass flowmeters, standard leaks, and residual
gas analyzers. In addition, we use this measurement capability to investigate
properties of materials and physical phenomena of fundamental interest.
Current projects include the development of an optical measurement of
gas concentrations for semiconductor process control, characterization
of a new high-precision laminar flowmeter to improve mass flow controllers,
start-up of a new leak-measurement service for the refrigeration, aircraft,
nuclear containment, and automotive industries, accelerated life-testing
of MEMS pressure sensors, as well as continuing efforts to reduce uncertainties
of primary and transfer standards. Contact: Albert Lee Quantitative Optical Measurements of Partial Pressures and Moisture Low-level gaseous
contaminants harm the outcome of chemical and materials manufacturing
processes, such as semiconductor manufacturing systems. Many commercially
available instruments for detecting these contaminants are not species
specific, are not sufficiently sensitive, or use detection techniques
that perturb the chemical composition and, therefore, compromise the measurement
of contaminant composition. We are seeking to develop quantitative optical
measurement techniques that have high species selectivity and sensitivity.
This effort strives to produce a new generation of species-specific, partial
pressure measurement standards with a particular emphasis on low-density
measurement of water, carbon dioxide, carbon monoxide, oxygen, hydrogen,
and methane. Our primary interests are optical measurement techniques,
including photon-induced ionization spectroscopies for partial pressures
less than 10-2 pascal and absorption spectroscopy in the range
of 1 kilopascal to 10-6 pascal. Initially, we are emphasizing
the use of cavity-ring-down-spectroscopy, an absorption technique for
the measurement of water, which should enable quantitative determinations
in the range of approximately 1 kilopascal to approximately 106
pascals. In addition to providing non-intrusive measurement techniques
for measuring partial pressure of contaminant gases, this research may
lead to a new generation of humidity measurement techniques and primary
standards for concentrations as low as 1 in 109. Contact: J. Patrick Looney or Roger D. Van Zee
Date
created:
September 28, 2001 |