Synchrotron X-ray Measurements

Our objective is to provide comprehensive descriptions of the
structure of advanced materials and devices by performing
synchrotron-based measurements to enable the development and
optimization of such materials and devices. Our research will
establish structure-property relationships for advanced materials,
thereby accelerating the introduction of these materials into devices
and systems with advanced functionality for a broad spectrum of
high-technology applications. 

Our approach is to apply state-of-the-art synchrotron measurement capabilities at the National Synchrotron Light Source (NSLS) and the Advanced Photon Source (APS) to generate structure data that cannot be measured by other methods. We collaborate with leading researchers from industry, other government agencies, and universities to address the nation’s most pressing measurement needs. The methods that we employ include: (1) near-edge X-ray absorption fine structure (NEXAFS) spectroscopy; (2) extended X-ray absorption fine structure (EXAFS) spectroscopy; (3) variable kinetic energy X-ray photoelectron spectroscopy (VKEXPS); (4) grazing incidence X-ray diffraction; and (5) small angle X-ray scattering and reflectivity. Methods (1) – (3) are available at the NIST beamlines at the NSLS, while methods (4) and (5) are located at the APS.

Impact and Customers:

• Establishing structure-property relationships for advanced materials is critical to the development and optimization of products in many technology sectors. Synchrotron measurements provide structure data that cannot be attained by other methods.
  

• Synchrotron measurements of the depth dependence of the interfacial structure e.g., chemistry and local bonding) in high dielectric constant gate stack devices have enabled SEMATECH to optimize processing of such devices.

• Synchrotron measurements have elucidated the surface chemistry of an environmentally friendly automotive oil additive produced by Afton Chemical.
  

• NIST researchers collaborate with more than 15 companies to provide synchrotron-based structure measurements of novel materials for next generation device applications.

One of the semiconductor industry’s “Grand Challenges” is to develop an alternative to the SiO2 gate dielectric. Integrated circuits exhibiting greater speed and lower power consumption are no longer attainable with ultrathin (= 2 nm) SiO2 gate dielectrics due to their high direct tunneling leakage currents. Our collaboration with SEMATECH has led to extensive evaluation of conductive metal gate electrodes and thin film metal oxides as promising high dielectric constant (highk) replacement insulator materials. We have measured core level binding energy spectra as a function of annealing temperature for AlO/SiO/Si gate stacks. An AlO/SiO interface effect is detected by the shift of the oxidized Si4+ 1s core peak to higher binding energy with increased annealing temperature, indicating interfacial modification of the Si sub-stochiometric chemical oxide. 

X-ray reflectivity and grazing-incidence small-angle X-ray scattering (GISAXS) were used to study the annealing behavior of ultrathin complementary-metal-oxide-semiconductor (CMOS) gate high-. dielectric HfO2 films grown by atomic layer deposition (ALD). Although dense, internal film structures exist, attributed primarily to 2 nm “missing island” porosity close to the substrate, and most likely associated with coalescence defects during initial ALD growth. Some larger features are also present, that may indicate a widespread modulation in the film density. Changes in film microstructure with annealing appear sufficient to affect CMOS gate dielectric performance after extended high temperature exposure and cycling.

We have used a combination of high resolution EXAFS and XRD to measure the local structure of strained LaSrCoO3 thin films grown under both compressive and tensile strain on substrates with dissimilar lattice constants. The lattice mismatch strain is found to affect both the bond lengths and the bond angles in the films. The popular double exchange model for ferromagnetism in these compounds provides a qualitative but not quantitative description of the measured changes in Curie temperature, with the predicted changes in Curie temperature being much smaller than observed. This finding demonstrates that a microscopic model for ferromagnetism with a much stronger dependence on structural distortion is needed.

An understanding of pentavalent uranium and U redox chemistry is of critical importance to the nuclear fuel cycle and to environmental concerns centered around man made and

Changes in Co-O bond length (EXAFS) and lattice constant (XRD).

natural sources of U ground water contamination. Although nature provides only a small number of examples of UV minerals, exotic UV species can form in the unusual geochemical environments existing in nuclear fuel storage facilities and in the vadose and ground water regions contaminated by leaking storage facilities. The synthesis, crystal structure and spectroscopic characterization of [UV(HO)(UVIO)O(OH)](H2O)4, a novel, stable UV/UVI oxide material not requiring the incorporation of carbonate, silicate, or organic ligands, were recently reported. EXAFS on a powdered form of this mineral was measured at beamline X23A2, verifying the mixed-valence of the U and the structure determined by single crystal x-ray diffraction.