| 摘要 |
972,511. Semi-conductor devices. WESTERN ELECTRIC CO. Inc. Sept. 23, 1960 [June 10, 1960], No. 32753/60. Heading H1K. A method of making a semi-conductor device comprises depositing epitaxially on a monocrystalline semi-conductor substrate of one conductivity type a layer of semi-conductor of the same conductivity type and subsequently diffusing significant impurity into the layer to convert part of it to the opposite conductivity type. In an example, a 111 face of a 0.002 ohm cm. N-type silicon monocrystalline wafer is prepared by polishing with silicon carbide, etching in a mixture of nitric and hydrofluoric acids, cleaning in hydrochloric acid, and washing in de-ionized water. The wafer is placed prepared face upwards on a shaped silicon block 20 in a water-cooled reaction chamber 11. Its surface is first freed of residual oxygen by heating to 1290‹ C. for 30 minutes in a flow of pure hydrogen at atmospheric pressure. After lowering the temperature to 1265‹ C. the hydrogen flow is diverted through silicon tetrachloride 17 contained in a liquid nitrogencooled flask and becomes saturated therewith. At the heated surface of the wafer the silicon tetrachloride and hydrogen react and high resistivity N-type silicon is epitaxially deposited. The resistivity of the deposited layer may, however, be modified by introduction of decomposable halides of activator materials, for example boron tribromide or phosphorus trichloride into the hydrogen flow. Boron is deposited on the epitaxial layer by heating in nitrogen and boron trioxide, and diffused in to form a P-type layer by heating to 1200‹ C. for 90 minutes in a mixture of oxygen and nitrogen. The substrate 45 (Fig. 3) is used as the collector zone of a transistor and is separated from the Player 41 forming the base zone by the high resistivity part 44 of the epitaxial layer unaffected by the diffusion. The Player is next provided with an oxide mask and heated at 1050‹ C. for 30-45 minutes in a flow of oxygen and phosphorous pentoxide to form a localized N-type emitter 42. Electrodes 46, 47, 48 are evaporated on and subsequently alloyed to the respective zones, unwanted parts of the epitaxial' layer etched away to leave the mesa configuration shown and wires 49, 50 thermocompression bonded to electrodes 47, 48. The switching time already lower than that of previous transistors may be further reduced by diffusion of gold into the substrate 45 and epitaxial zone 44, and quenching. A number of transistors may be simultaneously formed in similar manner on a common substrate which is then subdivided. |
