Contact: Fred McGehan, mcgehan@boulder.nist.gov
FOR IMMEDIATE RELEASE: NIST 96-47
Dec. 3, 1996
Contact: Fred McGehan (Boulder) NEW BREAKTHROUGH
(303) 497-3246 CRYOGENIC X-RAY
frederick.mcgehan@nist.gov MICROCALORIMETER
IMPROVES MICRO-
ANALYSIS TENFOLD
The Commerce Department's National Institute of Standards
and Technology has developed a revolutionary new X-ray micro-
calorimeter that offers tremendous promise for more precise
materials analysis, especially in the semiconductor industry.
The new microcalorimeter fits easily onto a commercially
available scanning electron microscope (known as an SEM),
conveniently operates even if the sensor is cooled to near
absolute zero and achieves X-ray energy resolution that is at
least 10 times better than conventional products. It was
developed by a team of scientists including John M. Martinis,
Gene C. Hilton, Kent D. Irwin and David A. Wollman at NIST's
Boulder, Colo., laboratories.
Already, the microcalorimeter has received positive reviews
from a technical working group at SEMATECH, the semiconductor
industry's manufacturing research consortium in Austin, Texas.
... The SEMATECH Analytical Laboratory Managers Working Group
believes that microcalorimeter detectors have the potential of
becoming the X-ray detector of choice for semiconductor
characterization applications," says Alain C. Diebold of
SEMATECH.
Currently, semiconductor energy dispersive spectrometer (or
EDS) detectors are the most commonly used X-ray spectrometers for
microanalysis; they typically count 3,000 X-ray photons per
second and measure the energy of each X-ray to within 100
electron volts. Better energy resolution between 10 and 20
electron volts is obtained by another commercial detector, the
wavelength dispersive spectrometer (or WDS). However, this device
is difficult to use and records X-rays only within one narrow
energy band at a time. The new NIST detector combines the
excellent energy resolution of a WDS with the operational ease of
a semiconductor EDS.
In a microcalorimeter, the energy of an X-ray is converted
into heat, and a measurement of the resulting temporary rise in
temperature gives the deposited photon energy. NIST's micro-
calorimeter consists of a normal-metal X-ray absorber in contact
with a thermometer that uses the rapid change in resistance of a
superconductor near its transition temperature to provide high
sensitivity. When biased by a voltage source,this transition-
edge-sensor (or TES) thermometer receives electrothermal feedback
(or ETF) that stabilizes its operating temperature in the
transition region and also reduces its response time.
The NIST detector presently achieves an X-ray energy
resolution of 10 electron volts at a count rate of 100 photons
per second. Researchers believe that the device eventually can
exceed both of these limits.
Such ability is critically important to the semiconductor
industry because a high-resolution system such as the NIST
microcalorimeter fully resolves the nearly overlapping X-ray
lines of silicon and tungsten. Therefore, manufacturers can make
the definitive identification of the tungsten silicide they need
to fabricate integrated circuits.
Two additional advanced technologies developed at NIST allow
the ETF-TES microcalorimeter to be incorporated into a fully
practical microanalysis system. The required 0.1 K operating
temperature is provided by a compact liquid-helium cryostat
that incorporates a novel two-stage adiabatic demagnetization
refrigerator. The ADR is unique because it attains a 0.05 K base
temperature working directly from the 4 K temperature of liquid
helium.
The microanalysis system also uses a sensitive SQUID
(superconducting quantum interference device) developed at NIST
as a preamplifier for the TES thermometer output. The SQUID
preamplifier provides the otherwise unattainable high output,
high bandwidth and low noise required to utilize the
micro-calorimeter fully.
When mated to a commercially available SEM, the ETF-TES
microanalysis system has recorded X-ray fluorescence spectra that
cannot be obtained easily by other methods. Of particular
importance to the semiconductor industry, the high-energy
resolution of the NIST system fully resolves the nearly
overlapping X-ray lines of silicon and tungsten, allowing
unambiguous identification of the tungsten silicide commonly
used in integrated circuits.
More generally, the improved energy resolution of the NIST
detector is expected to translate into a broad range of new
capabilities in microanalysis, including greater sensitivity,
higher spatial resolution and improved identification of light
elements. NIST is currently looking for industrial partners to
share in the commercial development of the ETF-TES
microcalorimeter. Patents have been or are being obtained on many
of the significant components; licensing arrangements are
encouraged. For more information on industrial collaboration,
contact John Martinis, Div. 814.03, NIST, Boulder, Colo.
80303-3323, (303) 497-3597, e-mail: john.martinis@nist.gov.
As a non-regulatory agency of the Commerce Department's
Technology Administration, NIST promotes U.S. economic growth by
working with industry to develop and apply technology,
measurements and standards.
-30-
News and general information on the National Institute of
Standards and Technology are available on the World Wide Web via
Internet at http://www.nist.gov.