Reaction Kinetics of Thermally Stable Contact Metallization on 6H-SiC
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Reaction Kinetics of Thermally Stable Contact Metallization on 6H-SiC Robert S. Okojie, Dorothy Lukco1, Yuan L. Chen2, David Spry3 and Carl Salupo3 NASA Glenn Research Center, Instrumentation and Controls Division 21000 Brookpark Road, M/S 77-1, Cleveland OH 44135; (216) 433-6522 1 AYT 20001 Aerospace Parkway, Brookpark, OH 44142. 2 Dynacs Engineering Company, Inc., 21000 Brookpark Rd. Bldg. 500 Brookpark, OH 44135 3 Akima Corporation, Fairview Park, OH 44126. ABSTRACT The growth kinetics of thermally stable Ti(100nm)/TaSi2 (200nm)/Pt (300nm) metallization on 6H-SiC was studied after heat treatment in air up to 700oC. Scanning electron microscopy (SEM) of the contact surface morphology reveals a two-dimensional network of features that is attributed to non-uniform oxide growth associated with the multigrain structure of the platinum overlayer. Auger electron spectroscopy (AES) and high-resolution transmission electron microscopy (HRTEM) identified three important reaction zones after initial 30-minute anneal at 600oC in nitrogen. One is the formation of a platinum silicide overlayer resulting from TaSi2 decomposition. The second is titanium silicide formation adjacent to the decomposed TaSi2. The third is pseudo-epitaxial Ti5Si3 at the SiC interface. Specific contact resistance values ranging from 10-4-10-6 Ω-cm2, remained stable after 200 hours at 600oC in air. Activation energies of 1.03eV for platinum silicide oxidation and 1.96eV for Ti5Si3 are obtained from Arrhenius plots. INTRODUCTION There is a growing interest in the use of silicon carbide (SiC) as the wide bandgap (WBG) semiconductor of choice for electronics and sensors in high power and harsh environments. However, unresolved reliability issues, prominent among which is stable contact metallization, temper this growing interest in SiC. Thermal stability of electrical contacts is a fundamental requirement for reliable electronics and sensing devices operating in harsh environments. Aggressive packaging methodologies have been adopted that provide hermetic sealing against contact oxidation, but these suffer from the drawbacks of added complexity, cost, and new reliability issues. Also, in the course of testing SiC devices, the need to expand the research effort beyond the traditionally focused investigation of the immediate metal/SiC interface has become evident. The traditional approach will not guarantee long term contact stability because it ignores broader failure mechanisms that exist elsewhere. The effort at NASA Glenn Research Center (GRC) has adopted a more global strategy by coupling interconnect, fabrication, and packaging principles toward achieving stable electrical contacts on SiC. The result presented here is an attempt to develop a thermochemical model of Ti/TaSi2/Pt metallization on 6H-SiC that will serve as a building block for future SiC device implementation at NASA-GRC. Analytical tools such as SEM, AES, and HRTEM are used to extract reaction parameters that allow for better understanding of the reaction kinetics. EXPERIMENTAL 6H-SiC, o
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