Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-08-27
2003-04-08
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S469000, C428S697000, C428S446000, C438S571000, C438S572000, C438S583000, C438S597000, C439S884000
Reexamination Certificate
active
06544674
ABSTRACT:
BACKGROUND
Electronic or electrical devices can be subjected to elevated temperatures in applications such as down-well drilling, in high power electronics, and in the automotive, aerospace, and process industries. Electronic devices fabricated from traditional materials used in the microelectronics industry, for example, a silicon semiconductor device with electrical contacts formed from aluminum, titanium, etc., are either unable to operate under high temperature conditions or deteriorate rapidly.
Silicon carbide (SiC) is presently under development for use in electronic devices that are subjected to high temperatures. Silicon carbide's material properties (large band-gap, high thermal conductivity, extremely high melting and decomposition temperatures, excellent mechanical properties, and exceptional chemical stability) exceed those of silicon and make it suitable for operation in hostile environments. Operation of SiC as semiconductor material, for example, is possible to temperatures as high as 1000° C. due to a band gap nearly 3 times larger than silicon (3.26 eV for 4H—SiC), thereby insuring low intrinsic carrier concentrations and operation within the dopant-controlled saturation regime required for semiconducting devices.
While SiC is stable and capable of functioning at elevated temperatures as well as in corrosive environments, a barrier to the widespread use of SiC-based microelectronics and microelectromechanical devices for high temperature applications has been the lack of stable electrical contacts thereon for making electrical connection to the devices. Virtually all metals, including the standard contact/electrode materials used in silicon-based devices (Al, Cr, Au, Ti, Pt, W, etc.), react with silicon carbide at elevated temperatures to form metal silicides and/or carbides. At a minimum, when an SiC device having such metal contacts is subjected to elevated temperatures above approximately 400° C. (depending on the metals), such reactions begin to change the resistance between the SiC and the contacts thereon. Over time, as the reactions continue, the change in resistance increases, which affects the device's performance. In more extreme cases, the entire contact layer degrades due to various combinations of: oxidation, decomposition, melting, evaporation, reaction with SiC and/or balling up on the surface.
Compositions, including metallic and refractory compound films such as TiW, TiN and TaC, have also been attempted for use as contacts on SiC devices. In some approaches, films such as Ni, W, Ti, Al, or Pt are first deposited on and then reacted with the SiC devices at temperatures well above the device operation temperature (about 900-1100° C.) to pre-form a more stable reaction layer. In other approaches, multilayer structures are utilized. The layers may, for example, serve to reduce the contact resistance, provide diffusion/reaction barriers, provide oxidation barriers, etc. However, these approaches suffer from intrinsic thermodynamic instability and do not form a stable electrical contact to the SiC surface. Consequently, due to reactions occurring at elevated temperatures, the layers have limited 1) lifetime, 2) maximum operating temperature, and/or 3) stability of device performance in the intended environment.
SUMMARY
The present invention provides an electrical contact for a silicon carbide (SiC) device or component including titanium silicon carbide (Ti
3
SiC
2
) material that is in thermodynamic equilibrium with SiC. This allows SiC devices to be operated in high temperature environments without the contact material reacting with the SiC, and the performance of the device deteriorating.
In preferred embodiments, the Ti
3
SiC
2
is deposited on the SiC device. In some embodiments, the Ti
3
SiC
2
material further includes at least one of zirconium (Zr), hafnium (Hf), aluminum (Al), germanium (Ge), chromium (Cr), vanadium (V), niobium (Nb), tantalum (Ta), molybdenum (Mo), scandium (Sc), gallium (Ga), indium (In), thallium (Tl), tin (Sn), lead (Pb), phosphorous (P), arsenic (As), sulfur (S), and nitrogen (N). In one embodiment, the electrical contact is an ohmic contact and in another embodiment, the electrical contact is a schottky contact.
The present invention is also directed to a semiconductor device including an SiC component and at least one electrical contact formed over at least a portion of the SiC component. The electrical contact is formed of a material that is in thermodynamic equilibrium with SiC. In preferred embodiments, the material comprises Ti
3
SiC
2
which is deposited on the SiC component. In some embodiments, the Ti
3
SiC
2
material further includes at least one of Zr, Hf. Al, Ge, Cr, V, Nb, Ta, Mo, Sc, Ga, In, Tl, Sn, Pb, P, As, S, and N.
In some embodiments, the SiC component is formed on a substrate layer. The SiC component or the substrate layer can be a micromechanical structure. The SiC component can include at least one doped SiC epitaxial layer formed on a portion of an underlying SiC layer to form a mesa. The SiC component can further include at least one doped SiC region implanted into the underlying SiC layer, wherein the at least one implanted SiC region and epitaxial layer each have an electrical contact thereon. The SiC component can also include an SiC substrate and an SiC buffer layer formed on the SiC substrate, wherein the underlying SiC layer is formed over the SiC buffer layer.
In another embodiment, the SiC component has an electrical contact on opposite sides thereof. The SiC component includes an SiC epitaxial layer formed on an SiC substrate. In yet another embodiment, at least one metallic layer is formed over at least a portion of at least one electrical contact. The at least one metallic layer forms at least one of a bondable layer for bonding electrical leads thereto, a diffusion barrier for preventing reaction with the at least one electrical contact, and an adhesion layer for promoting adherence of films deposited thereon.
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Goesmann, F., et al., “Metallization Studies on Ti3SiC2-Based Contacts on 6H-SiC,”J. of Materials Sci., Materials in Elec.: 103-107, article received Jul. 18 and accepted Nov. 9, 1997, (1998). No Month.
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Micak Richard
Spears Marlene A.
Tuller Harry L.
Boston MicroSystems, Inc.
Hamilton Brook Smith & Reynolds P.C.
Jones Deborah
Stein Stephen
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