Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Of specified material other than unalloyed aluminum
Patent
1991-10-25
1994-05-31
Hille, Rolf
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Of specified material other than unalloyed aluminum
257745, 257763, 257766, H01L 29400
Patent
active
053171900
ABSTRACT:
This invention describes a low resistance contact structure to n-type GaAs and a method for making such a contact structure. The contact structure is formed by depositing successive layers of Ni, Au, Ge, and Ni. A fifth layer is then deposited on the first four layers. The fifth layer is a metallic tungsten oxide. The metallic tungsten oxide is formed by sputtering tungsten onto the 4 layer stack in a low pressure argon plus oxygen atmosphere. The resulting 5 layer stack is then annealed in a rapid thermal anneal (RTA) process. The RTA process heats the stack for 5 seconds at 600 degrees. The resulting structure consists of an intermetallic NiGe compound having a small amount of a AuGa compound dispersed within it and being covered by a metallic tungsten oxide film. The oxygen from the metallic tungsten oxide film acts as a gettering mechanism to create gallium vacancies in the GaAs lattice structure during the RTA process. The oxygen forms a compound with gallium which is sandwiched between the metallic tungsten layer and the NiGe metallurgy. The sheet resistance of the contact metallurgy is low because the metallic tungsten oxide film is substantially thicker than that required to provide oxygen for the gettering process. The contact resistance to the n-type GaAs is low because the oxygen acts in a similar fashion to gold and creates more gallium vacancies in the GaAs. These vacancies are filled with an n-type dopant (Ge), supplied by the contact metallurgy, to create a better ohmic contact. The contact structure is reliable because there is a low gold content in the contact and because the nickel stabilizes the germanium which is not used for filling the gallium vacancies in the GaAs lattice.
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Fleischman Aaron J.
Lustig Naftali E.
Schad Robert G.
Aker David
Brown Peter Toby
Harper Blaney
Hille Rolf
International Business Machines - Corporation
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