Deposition, characterization, and thermomechanical fatigue of nickel aluminide and ruthenium aluminide thin films

Intermetallic thin films have properties that make them attractive for applications such as metallizations, high temperature coatings, microelectromechanical systems, and diffusion barrier layers. In this study B2 aluminide films (NiAl and RuAl) have been deposited and characterized. Both intermetallics could be deposited at temperatures near room temperature using cosputtering with an as-deposited resistivity of 45.5 +/- 1.5 muOcm for NiAl and 157 +/- 4 muOcm for RuAl. Ni/Al multilayers with a wavelength of 30 nm and below were fully reacted to form NiAl after annealing for 2 h at 400°C. These films had a resistivity of 15.5-26.7 muOcm (wavelengths from 15.4-30 nm) after a 4 h anneal at 400°C, and the lower values of resistivity correspond to films with larger wavelengths. In order for Ru/Al multilayers to be fully reacted at 400°C, wavelengths of less than 10 nm were required as well as longer annealing times (more than 11 h). RuAl from the 400°C reaction of Ru/Al multilayers had a resistivity of 71.6-123 muOcm. The lowest resistivity obtained for the B2 thin films was 11 +/- 0.1 muOcm, which was obtained for NiAl after a 20 min anneal at 800°C.;Both NiAl and RuAl have excellent bulk oxidation resistance, and in this study it was found that the oxidation resistance of the intermetallic thin films was superior to Al, Ni, and Ru metal films. The intermetallic films showed no observable surface changes (light microscopy) up to 500ºC in flowing oxygen and were conductive to higher oxidation temperatures (800°C for RuAl, 850ºC for NiAl) than Ni (500ºC), Al (600ºC), and Ru (800ºC, although vaporization may have begun at ∼700ºC).;The intermetallics NiAl and RuAl along with Ru and Au have been patterned into thin line structures and then tested using an alternating current (100 Hz) to induce thermomechanical fatigue (TMF) with 200 thermal cycles per second. RuAl samples were able to withstand higher cyclic values of Delta T than NiAl for comparable times to failure. Both NiAl and RuAl were able to withstand higher values of DeltaT than gold. The Delta T for tests on NiAl ranged from ∼300-520°C (T max: 400-600°C), with a time to failure of 100's of hours when DeltaT was near 300°C (T max: ∼400°C). Samples of NiAl that had a lower resistivity were able to withstand higher current densities due to reduced Joule heating. RuAl had a longer time to failure than NiAl at high testing temperatures (Delta T > ∼350°C), but trends in the data indicate that the time to failure at lower temperature may be higher for NiAl.;The use of Ni- and Ru-aluminide films combined with 2 different etchants for the fabrication of MEMS has also been investigated. Using a conventional wet etch for SiO2 sacrificial layers (HF) led to cracking and/or buckling depending on the stress state in the film (tensile/compressive). However, using a gas phase etchant for silicon sacrificial layers, XeF 2, free-standing regions could be formed that were crack free. Resonators were fabricated from co-sputtered NiAl and RuAl, and annealed multilayers of Ni/Al and Ru/Al, and first out-of-plane bending mode resonance was observed by using XeF2 etching. The best results were obtained for as-deposited NiAl that was co-sputtered at 1.5 mTorr and was under a compressive stress of ∼0.83 GPa. While the devices were not completely flat, they were free-standing, and improvements are expected by decreasing the stress in the co-sputtered films by increasing the sputtering pressure. The results for RuAl resonators are also promising as the films can withstand high compressive stresses (∼1.5 GPa, calculated from edge buckling), and improved performance from cosputtered RuAl is expected by increasing the sputtering pressure in order to decrease the film stress. (Abstract shortened by UMI.).