Understanding the structure, properties, and composition of semiconductors is an important aspect of a device's design and its operation in today's rapidly evolving electronics industry. This is particularly important as the dimensions of modern devices continue to shrink from the micron scale to the nanometer level. Measurements at these limits frequently require sophisticated instrumentation and expertise to elucidate the nature of what is occurring.

In the road map for CMOS development the phase out of SiO₂ as a gate dielectric is expected by 2005 and research is currently under way to replace SiO₂ with a high-K gate dielectric such as Tantalum pentoxide (Ta₂O₅) . During the course of research program in the Material Science and Engineering Department at NCSU, 2 nanometer wide layers were observed to form during the fabrication of TaO gate stacks on single crystal silicon which was capped with a layer of polycrystalline aluminum. In order to determine the nature of these layers compositional measurements at the 1 nanometer level had to to be performed upon the individual layers. Unfortunately, suitable instrumentation was not available at NCSU and as a result Prof. Maher and his students accessed ANL's TelePresence Microscopy (TPM) Collaboratory to characterize this material. Transmission electron microscopy cross-section samples were fabricated at NCSU and then shipped to ANL. At ANL the samples were mounted and loaded into the TPM Instrument where they were remotely studied by NCSU students and researchers.

Electron Microscope Image of a typical sample from this work.

Using access to both the Analytical Electron Microscope and the X-ray Energy Dispersive Spectrometer (XEDS), researchers were able to measure the local composition of the observed 2 nm layer either side of the Tantalum-based Hi-K dielectric. By stepping the electron probe across the interface and measuring the changing spectral profiles, it was determined that the layered structure consisted of silicon, tantalum and aluminum oxides.

Higher Magnification Image together with XEDS information identifying the elemental composition

The results obtained showed that evaporated Al was being incorporated into the dielectric gate-stack. As a result of this research, an amorphous TiN/polycrystalline Al gate electrode is now used in the current RT CVD Ta₂O₅process sequence for the fabrication of device structures in the NCSU study. Further work is in progress to elucidate the changes of this layer structure as a function of various process parameters.

Because to the availability of the resources via TelePresence Collaboration, at no time was it necessary for any researchers or students at NCSU to travel to ANL to accomplish these measurements. All of the observation and characterization was accomplished remotely using tools of the Collaboratory, which included remote conferencing, TelePresence operation of the instrument, and electronic notebooks, resulting in a savings of time and money.