Patent GB-1265932-A (GB)
IPC: H01L21/8238
Filed: 1970-07-14
Abstract: 1,265,932. Field effect transistors. RCA CORPORATION. 14 July, 1970 [21 Oct., 1969], No. 34118/70. Heading H1K. A pair of complementary insulated gateFET's are fabricated on a wafer substrate 10 (Fig. 4) of monocrystalline e.g. N-type silicon or on an epitaxial layer thereof, superimposed on a wafer of silicon, sapphire, or spinel; by coating with a masking layer 12 of silicon dioxide or silicon nitride or aluminium oxide by thermal reaction with oxygen or with silane and oxygen or water vapour; silane and ammonia, or aluminium chloride, carbon dioxide, and hydrogen; respectively. An opening is formed in the mask by partial coating with photoresist and etching out the uncoated portion with hydrofluoric acid or hot phosphoric acid as appropriate. The exposed surface is coated with a layer containing dopant of opposite conductivity type e.g. boron oxide by opposing to the surface a disc of boron nitride coated with oxide and heating to vaporizing temperature, and the dopant is diffused into the substrate by further extended heating to form a P-type well 18. Thereafter the oxide layer is etched off with e.g. hydrofluoric acid and a masking layer similar to that of the wafer is deposited over the well. Openings 20a, 20b are formed in the masking layer 12 by resist coating and etching, and a layer 22 of e.g. silicon dioxide containing dopant of the same type as the substrate, e.g. phosphorus, is applied to the masking layer contacting the substrate at the bottom of the openings 20a, 20b, to provide bounded N-type regions 22a, 22b; e.g. by thermal deposition from a gas containing silicon, oxygen and phosphorus. Other openings 24a, 24b are similarly opened in layers 22, 12 spaced from well 18, and a layer 26 of material e.g. silicon oxide containing dopant of opposite conductivity type to the substrate, e.g. boron, is deposited on layer 22 to contact the substrate at the bottom of the openings 24a, 24b to form a pair of bounded P-type regions 26a, 26b; e.g. by thermal deposition from a gas containing silicon, oxygen, and boron. Openings are etched in layers 26, 22, 12 to the substrate 10 between regions 22a, 22b and 26a, 26b respectively (Fig. 6, not shown) and the body is heated to diffuse the dopants into its surface, thus forming N-type source and drain electrodes 32a, 32b in the well, and P-type source and drain electrodes in the body of the substrate; oxygen being admitted to form channel insulation layers 36, 38 of silicon dioxide, (Fig. 7). Further spaced openings 40a, 40b and 42a, 42b are respectively etched through layers 26, 22 to the surface of the substrate at the N-type and P- type electrodes 32a, 32b; 34a, 34b respectively and a film of e.g. aluminium is evaporatively coated on layer 26 and the surfaces of the openings and channel insulants; the surplus being removed by etching to leave source, drain and gate contacts 44a, 44b, 44c; 46a, 46b, 46c for the two transistors respectively. Interconnecting strips may also be left between selected contacts. In a modification, (Fig. 10) a wafer of N-type monocrystalline silicon 44 is masked at 46 with silicon oxide, silicon nitride or aluminium oxide and opened to expose an area of the wafer; which is coated with a layer 50 of e.g. silicon oxide containing boron P dopant, by thermal deposition from a mixture of silane, oxygen, and diborane. The portion overlying the masking layer is removed by etching with hydrofluoric acid and ammonium fluoride over a resist to leave the layer 50 within the opening; which is covered with a further masking layer. A layer of e.g. silicon dioxide containing phosphorus N- type dopant is formed by thermal deposition from a mixture of silane, oxygen and phosphine, and is partially removed by etching over a resist with buffered hydrofluoric acid to leave element 52 overlying layer 50. A further layer of e.g. silicon dioxide containing boron P dopant is deposited on masking layer 46 and partially removed by etching over resist with buffered hydrofluoric acid to leave element 54 separated from elements 50, 52 and element 54 an overlying protecting element 52. Openings are formed through 54a, 52, 46, 50 and through 54, 46 to the surface of the substrate by simultaneously etching over a resist with buffered hydrofluoric acid, and thereafter the body is heat treated in e.g. nitrogen to diffuse boron from 50 into substrate 44 to form P-type well 60 (Fig. 12), phosphorus from 52 through 46 and 50 into the substrate to form N-type source and drain electrodes 62a, 62b in well 60, and boron from 54 through 46 into the substrate to form P-type source and drain electrodes 64a, 64b of a complementary FET. Oxygen is admitted during heat treatment to form channel insulation 66, 68 of silicon dioxide on the substrate at the bottoms of the openings. Pairs of spaced openings 70a, 70b and 72a, 72b (Fig. 13) are etched through 54a, 52, 46, 50 to the substrate surface at the N-type source and drain electrodes, and through 54, 56 to the substrate surface at the P-type source and drain electrodes, and metal film contacts 74a, 74b, 74c are formed in openings 70a, 70b and over insulation 66 while other metal film contacts 76a, 76b, 76c are formed in openings 72a, 72b and over insulation 68.