Patent GB-1393123-A (GB)
Title: Semiconductor device manufacture
IPC: H01L21/762
Filed: 1972-05-19
Abstract: 1393123 Semi-conductor devices PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 19 May 1972 [22 May 1971] 23700/72 Heading H1K In a semi-conductor device, at least one layer of semi-conductor material is formed in the face for monocrystalline, e.g. semi-conductor substrate body, and an insulation zone for isolating discrete parts of the semi-conductor layer one from another is formed comprising an insulant layer of insulation material inset with the semiconductor layer from its surface and extending to and adjusting at least in part a buried insulent layer of insulant material; the latter being located on part only of the substrate face and the composition and/or lateral extensions of the inset and buried insulation layers being of different constitutions. A semi-conductor device comprises a disc 1 of P-monocrystalline Si sliced from a rod and provided with a composite insulant layer 2 of boron doped SiO 2  overlain by undoped SiO 2 , deposited from SiH4 reacting with O 2  having BH 2  added. Windows are photoetched into the insulant in network form and As is indiffused over the insulant mask to form N-zones, and B is simultaneously indiffused from the insulant to form separating highly doped P-zones 4 intervening between the N-zones 5, 6, 7, 8. On the treated body as substrate a layer of Si 10 is deposited from SiH 4  + H 2  with added PH 3  to form epitaxial monocrystalline N-zones 12, 13, 14, 15 in the windows and polycrystalline separating zones 11 on the insulant. A layer 16 of Si 3 H 4  is then deposited from SiH 4  and NH3 with an underlying oxide layer, windows 20, 22, 24 are photoetched in network form over the polycrystalline zones and further strip windows 21, 23 over the monocrystalline zones, (Figs. 1 to 3, not shown). Further etching over the Si 3 N 4  layer as mask forms grooves 25, 26, 27, 28, 29 coincident with windows 20,21, 22, 23, 24 (Fig.4). Deep oxidized insulant layers 30, 31, 32, 33, 34 are formed in the grooves over the Si 3 N 4  layer as local mask by thermal oxidation in steam to adjoin oxide layer 2, and 31, 33 extend to buried N-silicon zones 6, 7, while polycrystalline elements 42, 44 of zone 11 are maintained to adjoin oxide layers 32, 34. Epitaxial N-type zones 13, 14 are divided into zones 36, 37, 38, 39 by layers 31, 33 (Fig. 5, not shown). An N-type connection persists under layers 31, 33 between zones 36, 37 and 38, 39 through buried layers 6, 7, and N-type islands within the P-type substrate 1 are separated by a network of insulation zones 30, 32, 34 and a buried insulant boron doped SiO 2  layer 2 adjoining the P-type zone 4. Layer 2 may alternatively be of Si 3 N 4  to serve as mask for the As diffusion of N-type zones 5, 6, 7, 8. Semi-conductor devices, e.g. transistors and diodes may be formed in the islands by etching off Si 3 N 4  layer 16 from regions 12, 36, 38, 15 and retaining it on regions 37, 39. Boron is surface indiffused to form P-type zones 56, 57, 58, 59 bounded by insulant and forming planar PN junctions with the underlying material 10 of which 57, 59 form transistor bases and 58, 38 the diode electrodes. Oxide layers 57, 52, 53, 54 are formed and the remaining nitride layer masks the zones 37, 42, 39, 44 (Fig. 6). Thereafter windows are formed in oxide layers 52, 54 through which P is diffused to form N-type emitters 62, 65 in base zones 57, 59 and highly doped N-type regions 63, 64 in zones 37, 39. Polycrystalline zones 42, 44 are heavily P doped throughout their thickness, and a layer of phosphate glass forms on the unmasked parts, which is etched off. Windows contacting base zones 57, 59 and electrode 58 are etched in over photoresist, and metal contacts 66, 67, 68, 69, 70, 71, 72 are applied respectively to emitter, base, collector, anode, cathode, base, and emitter (Fig. 8) which comprises a NPN transistor wherein emitter, zone 62 is provided in base zone 57 adjoining collector zone 36 of high ohmic epitaxial material adjoining a conducting N-type layer 6 underlying oxide layer 31 to contact N-type region 37 having overlying low ohmic N-type connection zone 63. Collector region 36 is thus connected to collector contact 38, and high ohmic region 37 connects contact zone 63 and buried layer 6. The P diffused N-type polycrystal zone 42 forms a low resistance connection between contact 68 and buried layer 6. Similarly the cathode 38 is connected to anode contact 70 over buried layer 7, the P-doped polycrystal zone 44, and the highly doped zone 64. In a modification, a P type monocrystal plate 101 is masked with Si 3 N 4  forming a windowed network through which As is diffused to form zone 103, and a superincumbent N-type Si layer is deposited epitaxially at 105 over the surface exposures and as polycrystal on the Si 3 N 4  masked portions. A Si 3 N 4  layer 110 overlies N- type layer 105 and is windowed longitudinally of the polycrystal strips to form a network, while part of the polycrystal zone 106 is peripherally masked by Si 3 N 4 . The Si layer 105 is etched through windows 111, 112, 113 over the Si 3 N 4  layer as a mask to form grooves 115, 116, 117 into half the depth of the layer 105 (Fig. 11) and is then thermally steam oxidized over mask 110 to form inset insulation layers 120, 121, 122 through windows to rest on the buried insulant layer 102. The remainder 123 of the polycrystal strip 106 is bounded by inset insulants 120, 121 and by Si 3 N 4  layers 110, 102, and the remainder 124 of polycrystal 108 is bounded by inset insulant 122 and epitaxial region 107 and buried Si 3 N 4  insulant 102. The part of layer 110 overlying region 124 and 107 is removed and P is indiffused to form highly doped N-type layer 125 in region 107 and to enter region 124 to a greater depth. Further portions of layer 110 are removed; and P-type Si is epitaxially deposited on the exposed surface of layer 105 to form monocrystalline parts 132, 134 and polycrystalline parts 131, 133, 135. A layer of SigN 4  136 is deposited on layer 130 and strip shaped windows 140, 141, 142, 143, 144 are etched therein. Grooves 150, 151, 152, 153, 154 are etched through the windows into half the thickness of layer 130 (Fig. 15) and deep oxidation over layer 136 as mask produces inset insulant layers 155, 156, 157, 158, 159 underlying the windows which adjoin respectively the buried insulant layers 120, 110, 121, 110, 122, and a polycrystal region 165 adjoins insulant layer 159, polycrystal region 124, and monocrystal P-type region 134. Layer 136 is removed, and an oxide masking layer is provided, which is peripherally removed to expose region 132 and widened to adjoin insulation inset 157. The layer is also removed from polycrystal zones 161, 162 and B is indiffused to form zone 166 along the edge of region 132 of low ohmic P-silicon, and is widened at 167. Simultaneous diffusion into polycrystal zones 161, 162 converts them to low-ohmic P- type (Fig. 17, not shown). The masking layer is removed, and a silicon oxide layer 170 is formed on the exposed Si by oxidation in wet oxygen, and is subsequently photoetched from the Si regions between inset insulants 158, 159. A window 171 is etched in the oxide region 132 into which P is indiffused over layer 170 as a mask to form a P-type emitter zone. Simultaneously a low ohmic surface N-zone 174 is formed in region 134, and P diffuses into exposed polycrystalline regions 163, 165 throughout their depths in high concentration; a thin phosphorus glass layer forming over the free surface parts (Fig. 18, not shown). A window etched in oxide layer 170 gives access to the wider part 167 of peripheral zone 166 of base region 132, and emitter window 171 is etched to expose surfaces of the N-type zones 163, 174, 165. Emitter contact 180, base contact 181, and collector contact 182 are provided on emitter 173, base 167, and N-type regions 163, 165, 174 by vapour deposition of A1. Thus the collector contact is connected to the uppermost N-type buried layer 125 also connected to the lowermost N-type layer 103. The collector and base contacts are also provided with overlying connection strips 182, 183. Finally (Fig. 19) the complete device comprises a NPN transistor laterally bounded by silicon oxide insulant zones 157, 159 adjoining the P-zone 101 isolating the underside of the transistor by PN junction with buried zone 103; buried oxide insulant 121, 122 being inset in the lower Si layer 105 and adjoining Si 3 N 4  layer 102. A flat collector-base junction between P-zone 132 and N-zone 107 is laterally bounded by insulant layer 157 and Si 3 N 4  layer 110. Base zone 132 is laterally surrounded by inset insulation layers 157, 158 so that low ohmic zones 166, 167 may be provided to surround emitter 173 along the edge of the base region. Buried polycrystalline strip 123 is entirely surrounded by insulant and is doped to act as a resistor, and inset polycrystalline zones 161, 162 also surrounded by insulant are highly P-doped to act as conductive connections. In a modification (Fig. 20, not shown) a semi-conductor device according to the invention comprises plural NPN transistors with a common buried emitter of similar construction, separated by inset insulant layers adjoining buried insulant layers, which define plural polycrystalline silicon islands into which B and P are successively diffused through oxide masks. Buried N-type zones form a common emitter and epitaxial P-type zones the collectors. In a further modification (Fig. 21, not shown) a semi-conductor device comprises a NPN and a PNP transistor with collectors interconnected by buried metal conductors of, e.g. Wo or Mo which may be passed over the buried insulation layers which may comprise Al 2 O 3 . Interconnections between the transistor elements may be effected by low doped polycrystalline Si as resistors or the high doped form as buried connectors.