Michael DiBattista

Determination of diffusion in polycrystalline platinum thin films

Grain boundary diffusion of titanium through platinum thin films has been carried out in the temperature range from 200 to 600 °C. Five different platinum/titanium bilayer thicknesses, from 35 to 800 A Pt, were annealed in 5% O2/95% N2. The accumulation of titanium at the platinum surface layer was measured by x-ray photoelectron spectroscopy (XPS) to determine the grain boundary diffusion coefficient (Db). Diffusivity values were calculated based on two different analysis methods assuming type C kinetics. For Pt layers thicker than 200 A, the activation energy (Qb) for titanium diffusion was found to be 118±15 kJ/mol (1.22±0.16 eV). For Pt layers thinner than 200 A, there was a thickness dependence on the diffusion kinetics, resulting in activation energies as low as 20±4 kJ/mol (0.21±0.04 eV). XPS results gave no evidence for any Pt-Ti alloy formation in these layers. The suppression of alloy formation may be attributed to the presence of oxygen at the Pt/Ti interface during layer deposition. The quanti...

Survivability of a silicon-based microelectronic gas-detector structure for high-temperature flow applications

Abstract This investigation addresses the important question of whether or not silicon-based micromachined chemical sensors are a viable option for gas sensing in harsh, high-temperature flow applications such as automotive exhaust. Data are presented on the thermal and mechanical stability and long-term functionality of micromachined silicon devices containing ultra-thin Pt/TiO x films supported on a heated multilayer silicon oxide/silicon nitride membrane. These gas detectors were originally designed for use in vacuum applications such as reactive ion etching systems. Significant modifications in device structure and materials are required to adapt these sensors for use in harsh thermal and chemical environments at elevated pressures. To test the long-term structural integrity of the sensors, they are subjected to a test protocol including pressure fluctuations, thermal shock, and mechanical vibrations. For characterization purposes, electrical resistance measurements, optical microscopy, atomic force microscopy (AFM), and Auger spectroscopy have been used. Our results indicate that properly designed micromachined silicon structures can survive long-term operation at high temperatures in ambient air, and can withstand rapid fluctuations of temperature, pressure, and flow rate.

In-situ elevated temperature imaging of thin films with a microfabricated hot stage for scanning probe microscopes

Abstract A microfabricated hot stage for a scanning probe microscope (SPM) has been developed to enable in-situ investigations of thin film specimens at elevated temperatures. With this hot stage, a SPM can now examine and test materials at high magnifications under conditions that closely resemble their true service temperature. The hot stage is capable of operating from ambient room temperature up to 800°C without damage to the microscope. With this device, topographical images of platinum supported titanium films, which are important for catalytic reaction studies, thin film gas sensor technology, and microelectronic applications, have been acquired at temperatures between 25–400°C. The average roughness of these films remained constant at 12.4±1.9 nm. The surface of the hot stage can be equipped with electrodes enabling four point probe measurements of conducting specimens as the temperature is increased and the surface is imaged. In-situ imaging of the titanium underlayer diffusing through the platinum film has been observed at 375°C. Titanium migration to the surface near this temperature is also shown on 35 A Pt/65 A Ti films with X-ray photoelectron spectroscopy (XPS). This stage can be retrofitted to any existing SPM to expand its current capabilities to include high temperature analysis of a wide diversity of materials, from biological samples, to polymers, and metals.

The Stress Change in Passivated Al Lines Due to the Reaction Between Ti and Al

The thin film reaction between Ti and Al-0.5%Cu to form TiAl 3 is common in the microelectronics industry. In this paper the stress changes in Al-0.5%Cu films at elevated temperatures during the reaction are measured. The changes are measured in blanket films as well as in passivated interconnect lines. Results show that in blanket films the Al-0.5%Cu does not experience any stress change due to the reaction. However in passivated lines, where the layers are not allowed to relax in the normal direction, tensile stresses build up in the Al-0.5%Cu due to the volume shrinkage that happens when these films react.