Nanocalorimetry Measurements

Our objective is to develop nanocalorimetry as a method for measuring heats of reaction with nanojoule sensitivity, in order to detect reactions and quantify reaction thermodynamics and kinetics in multilayer structures. Nanocalorimetry will enable measurement of the interfacial stability of buried interfaces found in multilayered thin film structures such as the advanced gate stack of silicon integrated circuit devices.

Thin film interfacial stability may be compromised by interfacial reaction, structural transformation, or interdiffusion. Existing methods for detecting such phenomena require specialized high-energy, high-brightness electron or optical probes, and do not allow measurement under actual device operating conditions. We will establish nanocalorimetry as a quantitative technique for detecting interfacial degradation phenomena by developing MEMS-based nanocalorimeter sensors and instrumentation, calibration procedures, and reference materials for these devices. We will perform extensive thermal modeling of the nanocalorimeter devices in order to quantify the accuracy and precision of data generated by these devices. The applicability of nanocalorimetry will be demonstrated with measurements on industrially relevant materials such as integrated circuit device structures and hydrogen storage alloys. A future goal will be the design of dense arrays of small nanocalorimeters to combinatorially screen candidate materials for these applications.

Impact and Customers:

• Advanced electronic and optoelectronic materials are used in highly integrated structures such as multilayer thin film stacks. The performance of devices containing such structures is critically dependent on the stability of the thin film interfaces. Nanocalorimetry can determine the stability of multilayer thin film structures by measuring the thermal signature accompanying interfacial reactions.

• NIST nanocalorimeters have applications for the advanced gate stack multilayer structure of next generation silicon integrated circuit devices.

• NIST nanocalorimeters are also used to quantify the thermodynamics and kinetics of H₂ uptake and release in H₂ storage alloys to be used for onboard vehicular solid-state storage of H₂.

• Potential customers for this project include member companies of industrial consortia such as SEMATECH and USCAR.

We are investigating two types of MEMS nanocalorimeter devices as part of this project. The first device was adapted from a NIST microcalorimeter design (S. Semancik, Chemical Science and Technology Laboratory, CSTL); with this design, we have achieved measurement sensitivity levels < 10 nJ, demonstrated with a Pb melting point standard. The second device design, whose process flow has now been transferred to the NIST nanofabrication facility, came to us through our collaboration with the University of IIlinois. Although this device is easier to fabricate, it is larger, and has thus far enabled measurement sensitivities no lower than about 400 nJ. Going forward, we will design and produce new types of nanocalorimeters from the "ground up", based on thermal finite element analysis modeling and consideration of the specific materials systems to be investigated. Further, we are continuously enhancing the new nanocalorimeters to make higher temperature ( 700 °C) combinatorial measurements on dense arrays of smaller devices.

CSTL-type MEMS Nanocalorimeter



U. Illinois-type MEMS Nanocalorimeter

The nanocalorimetry project is currently driven by two measurement challenges: determining thermal stability of multilayer thin films and assessing H2 desorption in alloys for solid state storage of H2. We began our study of multilayer thin films with a model materials system that also is of great importance to the silicon microelectronics industry (as a source/drain contact metallization), nickel silicide. Separate Ni and Si thin films were deposited on the nanocalorimeter, and were allowed to react during a temperature ramp. Since the devices have very small thermal mass, they can be ramped at rates as great as 50,000 °C s-1; such high rates may be necessary to adiabatically capture the thermal signature of the reaction. We measured a reaction enthalpy of -8.1 mJ for our Ni-Si multilayer sample, as compared to a calculated value of -8.9 mJ. The agreement is within 10% and may be improved if undetected conduction and radiative heat losses can be accounted for by finite element analysis modeling.

Nanocalorimetric data for Ni-Si thin film reaction to form nickel silicide, showing an endotherm starting at 35^˚C, and exotherms starting at 235˚C and 480˚C

We are also studying the thermodynamics and kinetics of H2 desorption in alloys to be used for onboard solid-state storage of H2 for fuel cell powered vehicles. Such data are essential to the design and successful implementation of H2 powered cars.

Nanocalorimetric data for H₂  desorption from a Pd_0.1Au_0.9 thin film, showing the H₂ desorption endotherm beginning at 95˚C