| 摘要 |
909,869. Semi-conductor devices. WESTERN ELECTRIC CO. Inc. June 3, 1959 [June 9, 1958], No. 18920/59. Class 37. A silicon body into which an impurity is to be introduced is subjected to an atmosphere including the impurity in the vapour form for such a time and at such a temperature that a layer of glass is produced on the surface of the body with an impurity diffused layer beneath the glass; the glass is then removed by etching and the body heated so as to cause the impurity to diffuse further into the body. The Specification states that the concentration of the impurity measured after removal of the glass is found to be a constant substantially independent of both vapour pressure and temperature of the silicon. In the arrangement shown in Fig. 1, the silicon body is mounted on a base 12 with a closely fitting lid and made of fused alumina or platinum and is placed in a silicon furnace tube 11 through which flows an atmosphere which is interchanged with that in the box. Where boron is the impurity the body is first etched and plated or may have an oxidized layer produced on its surface as described in Specification 809,644. Boron trioxide is plated in the bottom of the box and the silicon body 13 placed on a platform 15. The box restricts the volume in which the source material vaporizes so as to provide an excess of impurity in contact with the silicon. The diffusion step may be conducted at a temperature in the range 700‹ to 1300‹ C. At temperature below 1150‹ C. the atmosphere may be an inert gas, e.g. nitrogen argon or helium; at temperatures above 1150‹ C. oxygen must be introduced to prevent the silicon from pitting. A dark deposit which sometimes occurs may be avoided by using a mixture of boron trioxide and silicon dioxide. The resultant body has a layer in which the impurity predominates and a layer of glass. The glass is removed by means of an etchant which does not attack the silicon, e.g. hydrofluoric acid and is then placed on a platform in a furnace of the type described above, and heated for a time and temperature determined by the degree of diffusion required in an atmosphere of pure oxygen or of oxygen and an inert gas. A temperature of from 700‹ to 1350‹ C. is suggested but 1100‹ to 1300‹ C. is preferred. In an arrangement for depositing phosphorous (Fig. 2) from phosphorous pentoxide in a container 29 kept by a heating coil at 275‹ to 230‹ C. a gas containing the phosphorous vapour flows over the silicon 22 which is maintained at from 700‹ to 1300‹ C. The Specification indicates the possibility of using antimony. Whatever the impurity it must be capable of forming a glass with silicon. If the impurity source is not an oxide either pre-oxidized silicon or an oxygen atmosphere must be used. Specification 816,799 also is referred to. |
