Patent GB-941729-A (GB)
Title: An improved semiconductor alloying process and apparatus therefor
IPC: H01L21/00
Filed: 1960-10-25
Abstract: 941,729. Semi-conductor devices. TELEGRAPH CONDENSER CO. Ltd. (Sprague Electric Co.). Oct. 25, 1960, No. 36584/60.. Heading H1K. In a process for producing two or more alloy junctions in a semi-conductor body the body is brought into contact simultaneously with two or more masses of molten activator material in apertures of containers therefor, the apertures each being spaced from the body by a distance not greater than the least dimension of the aperture. The masses dissolve the contacted portions of the body and after at least partial recrystallization of the solutions thus formed the body and attached masses of activator material are withdrawn from the apertures. In an example, a 1 ohm. cm. antimony doped N-type germanium wafer with faces in 111 crystallographic planes is first lapped and acid etched and then picked up by a suction tube and placed in argon between two lagged electrically-heated capillary tubes 12, only one of which is shown in Fig. 1. Indium and indum gallium alloy is then forced out of the respective capillaries by plungers 14 (or by gas pressure) to contact the wafer. After 30 seconds the plungers are retracted to withdraw the indium and the residual material allowed to recrystallize. The plungers 14 may be apertured to allow wires to be fused to the contacts in the same step, or heavy gauge silver wires pressed against the wafer by the plungers and subsequently left behind. In an alternative method the suction tube is provided with tiny holes permitting argon to be blown therethrough to cool the wafer and a column of indium in one of the capillaries so that on withdrawal the wafer carries a long indium filament. To assist in the recrystallization process a current may be passed through the junction between the activator material and wafer to cool it by the Peltier effect. The amount of activator material left on the wafer may be predetermined by providing a constriction or a sharp change in cross-section near the end of each capillary so that the indium breaks off at this point. The system is further improved by providing a small capillary vent at the constriction so that when the column of activator material breaks the resulting local vacuum tending to lift the remaining material off is broken. An alternative system shown in Fig. 11 is to interpose a plate with an aperture 51 normally in register with the capillary bore and to move the capillary sideways to the position shown to break the column. Wetting of the contacted areas of the wafer is facilitated by pre-plating with indium. Indium-gallium, indium-aluminium, or an alloy of 2 to 40 parts by weight indium to 1 part germanium may be used in place of indium in the above processes. If a P-type silicon or germanium wafer is used suitable alloying materials are lead-arsenic and lead-antimony. To form a PNP arrangement under one of the contacts a P-type wafer is used and alloy of 97% indium, 3% arsenic provided in one capillary. A pair of dissimilar alloy junctions may be formed on a raised island of semi-conductor by using a capillary with an annular bore surrounding the main bore (Fig. 5) or the arrangement shown in Fig. 4 comprising holes or parallel slits 44 in adjacent alloy reservoirs 43.