1,165,029. Semi-conductor devices; resistors. RADIO CORPORATION OF AMERICA. 29 Nov., 1966 [2 Dec., 1965], No. 53493/66. Headings H1K and H1S; In a monolithic semi-conductor microcircuit a P(N) type region 8, e.g. comprising a resistor, is surrounded by a portion of an N(P) type region 6 isolated laterally from the remainder of the crystal by a P(N) type zone 10. An N+(P+) zone 12 is provided between the isolated portion of the region 6 and the zone 10, at least partially separating the two, and thereby minimizing the detrimental effect of the parasitic PNP(NPN) transistor formed by the regions 8, 6 and the zone 10. In the form shown, the region 6 is epitaxially deposited on a highly antimony- or arsenic-doped N + epitaxial layer 4 on a boron-doped P-type silicon substrate 2. Using an oxide masking and photoresist technique a rectangular annular layer of BBr 3 is vapour deposited on the surface in preparation for formation of the isolation zone 10, and a similar layer of, e.g. POCl 3 is vapour deposited prior to formation of the zone 12. Subsequent heating at 1165‹ C. causes the impurities to diffuse in, partly forming the zones 10, 12. Boron nitride is deposited on the surface, through a suitable oxide mask, and boron is diffused in at 1100‹ C. to form the region 8, this heating stage causing the further diffusion required to complete the zones 10, 12. Metal contacts 28 are then applied through an insulated oxide coating 26. In an alternative embodiment, the substrate 2 is also of N-type conductivity, and in this case the isolation zones 10, 12 extend throughout the wafer thickness. The highly doped N + type region 4 need not extend throughout the crystal, and may instead comprise a pocket diffused into the substrate 2. If the N-type layer 6 is sufficiently thick the N+ type layer 4 may be dispensed with entirely. The resistor described may be included in a monolithic circuit comprising diodes, transistors, capacitors &c.
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