Integrated circuit

Claim 1

An integrated circuit comprising a semiconductor body having an epitaxial semiconductor layer of a first type conductivity and of a given thickness on a semiconductor substrate of a second opposite type conductivity, isolation zones of the second type conductivity extending through the epitaxial layer to define in the epitaxial layer a plurality of first type conductivity isolated islands, plural circuit elements selected from the group consisting of resistors, capacitors, diodes and transistors being located in said islands, at least one of said circuit elements being a resistor formed by the first type epitaxial layer material of one of said islands, means for effecting electrical connection to spaced points of the epitaxial layer material in said one island to form resistor connections for said resistor, the doping near the surface of the epitaxial material in said one island where it remains of the first type being substantially homogenous, and a surface boundary zone of the second type conductivity located in the isolation zone and adjoining a substantial part of the boundary of the said island containing the resistor forming a P-N junction determining the overall resistance of the resistor between its connection points, said boundary zone having a depth of penetration which is smaller than the thickness of the epitaxial layer, the concentration of second type dopants in the isolation zones being greater than the concentration of first type dopants in the isolated islands, and the concentration gradient of second type dopants at the boundary zone-island P-N junction being substantially greater than that at the isolation zone-island P-N junction.