Patent GB-997996-A (GB)
Title: Field effect device and method of manufacturing the same
IPC: H01L21/205
Filed: 1963-01-16
Abstract: 997,996. Semi-conductor devices. MOTOROLA Inc. Jan. 16, 1963 [Feb. 19, 1962], No. 1981/63. Heading H1K. A field effect device is manufactured by epitaxially depositing two layers of semi-conductor material on a substrate and then diffusing impurity into the layers to form a source and a drain which define the limits of the channel and gate formed by the layers. As shown, Fig. 1, a P-type substrate 11 has N-type layer 12 and P-type layer 13 epitaxially deposited on one face. As shown, Fig. 2, layer 13 is masked, 23, and N-type impurity is diffused into the layers to form heavily doped N+-type source and drain regions 16, 17. The remaining portion of the P-type layer forms the gate 19 and the portion of the N-type layer directly below this forms the channel 18. The process is used to manufacture a plurality of field effect devices from a monocrystalline wafer of silicon doped with boron which is heated to 1180‹ C. in a stream of hydrogen into which is introduced silicon tetrachloride or trichlorosilane vapour doped with phosphine vapour to epitaxially deposit an N-type layer, after which the impurity is changed to diborane vapour to epitaxially deposit a P-type layer on top of the N-type layer. The wafer is then heated in steam to form a coating of silicon dioxide which is then selectively removed using a photoresist method, phosphorus is diffused into the layers to form N+-type sources and drains, and the remaining oxide layer is removed. The wafer is then sliced into individual units which are mounted on a header, connections made to the source, drain and gate regions, and the device is encapsulated. The drain is in the form of a rectangle surrounded by the gate and channel layers which are surrounded by the source. Impurity may be diffused into the outside edges of the sources to form P+ type regions connected to the substrate thus making all the junctions emerge on the upper face of the wafer so that it can be divided up into individual units by scribing and breaking without damaging the junctions. Devices of this kind can be mounted on the header using an electrically insulating but thermally conductive layer of alumina or beryllia, and ohmic connections can be made to the various regions on the upper face only. Alternatively a current limiter can be produced by making a single metallic contact to all the regions except the drain which has a separate contact. A mesa field effect device can be produced by etching the wafer of Fig. 1 and then diffusing in the source and sink regions. Preferably the epitaxially deposited layers and the substrate have about the same impurity concentration so that the junctions formed do not change position if inter-diffusion of the doping impurities occurs. Also the sheet resistivity of the channel of a device may be measured and if it is found to be too low the wafer can be heated to 1100‹ C. to cause inter- , diffusion of impurities so that the sheet resistivity of the channel is increased without changing the positions of the junctions. Devices can be manufactured with regions of opposite conductivity type to those mentioned.