Solderable backside ohmic contact metal system for semiconductor devices and fabrication process therefor

Abstract

Abstract 1,193,532. Semi-conductor devices. INTERNATIONAL BUSINESS MACHINES CORP. 8 Jan., 1968 [13 Jan., 1967], No. 1001/68. Heading H1K. [Also in Division C7] Electrical contact is made to a semi-conductor region with an impurity concentration of at least 1018 atoms cm.<SP>-3</SP> by depositing first a film of chromium, aluminium or titanium and then a film of nickel, silver, copper or copper chromium alloy. In one embodiment an antimony-doped N+type silicon wafer carrying an epitaxial N type layer is first provided with a silicon oxide coating by heating in dry oxygen and then in steam, or by R.F. sputtering, or with a layer of silicon nitride or alumina. Base and emitter regions are then formed by successive diffusions of boron and phosphorus into the N layer using standard planar techniques, the second diffusion doping the emitter and collector contact region with 5 Î 10<SP>20</SP> atoms/c.c. of phosphorus. Aluminium base and emitter contacts are next provided by vapour deposition overall followed by form-etching and sintering. Glass is subsequently deposited over the contacted face of the wafer in two stages of R.F. sputtering each followed by a firing stage. The wafer is then inverted in an evacuated vapour deposition chamber and its back collector contact face coated with successive layers of chromium, copper and gold of specified thickness while the wafer is held at 200-250‹ C. Holes are next etched through the glass layer to expose the aluminium contacts upon which similar layers of Cr, Cu and Au are then deposited through masks followed by layers of lead-tin solder by means of which nickel-plated copper balls are attached to the contacts. Finally the completed elements are attached to silver palladium lands on an alumina mounting plate and the ball contacts connected via nickel-plated copper strips to adjacent lands using lead-tin solder. In alternative planar diode and transistor embodiments the outer layer of gold is omitted.

Inventors

• 👤 Paul P Castrucci
• 👤 Robert H Collins
• 👤 Robert G Shepheard

Bibliographic Details