| 摘要 |
1,248,051. IGFETs. POST OFFICE. 3 March, 1969 [1 March, 1968], No. 10100/68. Heading H1K. An IGFET is formed by depositing a layer of P(N) type on a layer of N(P) type material and diffusing impurity into it to form a second N(P) layer, forming a trough extending through the other layers into the first N(P) layer, providing insulating material on the groove walls and then depositing a metal electrode on the insulation where it overlies the P(N) layer. A typical device, Fig. 3, is formed by epitaxially depositing a 1 ohm. cm. N-type silicon layer 8 6 Á thick on a 0.005 ohm cm. silicon substrate 7 and then forming a P-type layer 11 by planar diffusion techniques. Grooves 15 extending to the substrate are formed by photoresist and etching steps and then the exposed surfaces of the grooves coated with oxide 1500 Š thick. The interdigitated drain 20 and gate 21 electrodes and electrodes 19, all of which extend over an overall oxide layer to enlarged contact pads are then shaped by etching from an evaporated layer of aluminium. The substrate is attached to a header constituting the source electrode. Source-drain capacitance may be reduced by leaving the bases of the grooves free of electrode metal. Another way of reducing the capacitance is to use a lightly doped N-type substrate with a heavily doped P-type surface layer functioning as source, the groove extending through this layer. In another modification the oxide insulant is absent from the bases of the grooves which are covered with a silicon nitride layer which also extends over the oxide on the groove walls. This layer can break down reversibly to short the gate to the source at voltages less than the breakdown voltage of the gate insulation proper and thus fulfils a protective function. In yet another arrangement which enables several devices with mutually isolated sources to be formed in a single body the substrate is again of N-type with diffused P-type inclusions constituting the sources which can be contacted at the bases of etched grooves. Finally the vertical walls of the grooves may be replaced by inclined walls, resulting in some cases in V-shaped grooves, by orientating the substrate surface in a 100 plane and using hydrazine hydrate to etch the grooves. |
