Phosphorus-doped silicon semiconductors

摘要

1,020,946. Phosphorous-doped silicon device. WESTINGHOUSE ELECTRIC CORPORATION. July 9, 1964 [July 24, 1963], No. 28382/64. Heading H1K. A semi-conductor junction device is made by forming a darkened layer on a surface of a silicon semi-conductor wafer or on selected portions thereof and diffusing phosphorus through the darkened layer. In a specific embodiment a silicon body 10 doped with B, A1, Ga, or In is lapped or cleaned by an etchant e.g. a mixture of HF, HNO 3 and CH 3 CO a H or hot NaOH solution and then partially masked with a wax or photo-resist material. The exposed portion of the body 10 is electrolytically darkened 14, the masking material removed and the body subjected to phosphorus diffusion to give a diffused layer 16, of phosphorus which is deeper under the darkened layer. The surface layer of N-type material 16 on the side and bottom of the body 10 may be removed and a groove formed on the upper layer to give two separate N-type regions. In other embodiments (Figs. 9 and 12, not shown) a three junction device and a field effect transistor having a gate region of gradually varying depth are made. The masking material may be left in place while the electrolytic darkening takes place. Alternatively, no mask may be applied but rather only a portion of the semi-conductor body contacted with the electrolytic bath e.g. in the case of the field effect transistor, the body is slowly withdrawn thus giving a darkening to different extents. Starting materials of resistivity less than 10 ohm. cm. are preferably whilst in the case of materials of resistivity greater than 1 ohm cm. illumination whilst darkening is advantageous. A current density of less than 100 ma. cm.-1 is preferable. The electrolytic darkening bath may be conc. HF with or without glycerine or ethylene glycol. The phosphorus diffusion may be carried out using elemented phosphorus in a closed tube, P 2 O 5 in an open tube gas flow system or a solution of P 2 O 5 in ethylene glycol.