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US 5,994,194 AGranted
Self-aligned base ohmic metal for an HBT device cross-reference to related applications
AssigneeTRW Inc.
InventorMichael D. Lammert
Life of this patent
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AssigneeTRW Inc.
InventorMichael D. Lammert
Estimating the term…
A relatively simple method for providing relatively close spacing between the emitter mesa and the base ohmic metal of a heterojunction bipolar transistor (HBT) on a relatively uniform basis. An emitter and base layer are epitaxially grown on a substrate. An emitter mesa is patterned with an i-line negative photoresist using conventional photolithography. Baking before and after exposure is used to form a resist pattern with a re-entrant profile having about a 0.1 .mu.m resist overhang. The emitter layer is then etched with a wet etch and or isotropic dry etch to expose a portion of the base ohmic metal to make contact with the base. A second layer of an i-line negative photoresist is applied over the first photoresist. The second layer is used to pattern the base ohmic metal mask. The base ohmic metal is deposited by evaporation. The resist is stripped from the emitter mesa and the non-base ohmic metal regions which lifts the metal deposited on the resist leaving the metal in the base ohmic metal regions, aligned to the emitter mesa at a uniform spacing.
A method for controlling the spacing between an ohmic metal and an emitter mesa on an integrated circuit formed with a substrate and a plurality of vertically stacked epitaxial layers, including a base layer and an emitter layer formed on top, the method comprising the steps of:
A method for controlling the spacing of the base ohmic metal relative to an emitter mesa on a heterojunction bipolar transistor (HBT) having a substrate and a plurality of vertically stacked epitaxial layers including a base layer, and an emitter layer formed on top, the method comprising the steps of:
Dependencies are inferred from the claim text.