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Army Research Laboratory scientists have developed high-performance, high-reliability ohmic contacts for high-temperature and high-voltage applications. The patented technology is available via license agreement to companies that would make, use, or sell it commercially.
Semiconductor devices require high-quality, low-resistivity, thermally stable, and reliable n- and p-type ohmic contacts. Ohmic contacts are essential for the transfer of signals between the silicon carbide (SiC) devices and the external circuitry. Metallization design, selection, and method of deposition heavily influence the electrical and physical properties of ohmic contacts.
The most common metal deposition methods include electron-beam evaporation, sputtering, and thermal evaporation. Sputtering and e-beam evaporation are preferred over thermal evaporation because the latter involves either a resistance-heated source or an evaporation source which results in contamination of the charge. This contamination leads to unwanted impurities, which adversely affect the electrical properties of the contact metal film.
There are several critical requirements to achieve high-performance, reliable SiC-based devices. The ohmic contacts must possess a reproducible low-specific contact resistance value, must not significantly perturb device performance, possess excellent mechanical properties, and be temporally, environmentally, and thermally stable. Additionally, the contact metal-semiconductor interface must be uniform, shallow, and abrupt.
ARL researchers have developed a nickel silicide (Ni2Si) ohmic contact that is formed on n-type silicon carbide (n-SiC) semiconductor substrates via pulsed laser ablation deposition. A SiC substrate is optionally masked to expose the required deposition areas. The SiC substrate is mounted in a vacuum chamber in the sample position separated by a gap from the source Ni2Si target. A laser beam is focused onto the rotating source target with a 45° incident angle and the source target is ablated to produce a Ni2Si plume that is deposited onto the SiC substrate. The result is a Ni2Si ohmic contact having the same stoichiometric composition as the source target.
- Excellent current-voltage (I-V) characteristics
- Abrupt void-free contact-SiC interface and smooth surface morphology
- Absence of residual carbon within the contact layer or interface
- Businesses can commercialize the technology by licensing U.S. Patent 7,297,626 from the Army
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