Protection device utilizing one or more subsurface diodes and associated method of manufacture

A protection device for an integrated circuit that has a first supply terminal for receiving a first supply voltage, a second supply terminal for receiving a second supply voltage greater than the first supply voltage, a protected circuit component coupled to the supply terminals and formed from part of a semiconductor body having an upper surface along which electronic elements of the component are located, and an information terminal coupled to the component for transferring information between it and the external environment;

• the device comprising a diode formed from part of the body, the diode either having an anode and a cathode respectively coupled to the first supply terminal and the information terminal or having an anode and a cathode respectively coupled to the information terminal and the second supply terminal, characterized in that:
• an isolation mechanism recessed into the body below the upper surface laterally separates a group of active semiconductor portions of the body from one another along the upper surface, the isolation mechanism substantially consisting of dielectric material at least where the isolation mechanism adjoins material of the body;
• and
• the anode and the cathode respectively comprise a P-type zone and an N-type zone that extend from the upper surface down respectively into a pair of the active portions to form a PN junction that lies entirely below the upper surface, at least one of the zones extending vertically through the active portion for that zone and into material of the body below the isolation mechanism.

A method of fabricating a protection device for an integrated circuit that comprises a first supply terminal for receiving a first supply voltage, a second supply terminal for receiving a second supply voltage greater than the first supply voltage, a protected circuit component coupled to the supply terminals, and an information terminal coupled to the component for transferring information between it and the external environment;

• the protection device comprising first and second diodes, the first diode having an anode and a cathode respectively coupled to the first supply terminal and the information terminal, the second diode having an anode and a cathode respectively coupled to the information terminal and the second supply terminal, characterized by the steps of:
• introducing (a) N-type dopant into a semiconductor substrate of a selected conductivity type through its upper surface at a pair of separate locations and (b) P-type dopant into the substrate through its upper surface at a pair of separate locations;
• growing an epitaxial semiconductor layer on the upper surface of the substrate to form a semiconductor body comprising the substrate and epitaxial layer;
• creating a dielectric isolation mechanism that is recessed into the body below its upper surface so as to laterally separate a group of active portions of the body from one another and establishing (a) a pair of N-type connection regions that extens from the upper surface of the body respectively into a pair of the active portions and (b) a pair of P-type connection regions that extend from the upper surface of the body respectively into another pair of the active portions;
• and
• causing the preceding dopants to diffuse further into the body during at least the foregoing steps to form (a) a pair of N-type buried regions and (b) a pair of P-type buried regions that respectively meet the N-type buried regions to define a pair of separate PN junctions that lie fully below the upper surface of the body, the N-type buried regions respectively meeting the N-type connection regions to form the cathodes, the P-type buried regions respectively meeting the P-type connection regions to form the anodes.

A method of fabricating a protection device for an integrated circuit that comprises a first supply terminal for receiving a first supply voltage, a second supply terminal for receiving a second supply voltage greater than the first supply voltage, a protected circuit component coupled to the supply terminals, and an information terminal coupled to the component for transferring information between it and the external environment;

• the protection device comprising a diode either having an anode and a cathode respectively coupled to the first supply terminal and the information terminal or having an anode and a cathode respectively coupled to the information terminal and the second supply terminal, characterized by the steps of:
• introducing N-type dopant into a part of a P-type semiconductor substrate through its upper surface;
• annealing the substrate to cause the N-type dopant to diffuse further into the substrate so as to form an N-type portion along the upper surface of the substrate;
• introducing P-type dopant into a part of the substrate at least partially surrounded by the N-type portion up to the upper surface of the substrate;
• growing an epitaxial semiconductor layer on the upper surface of the substrate to form a semiconductor body comprising the substrate and the epitaxial layer;
• creating a dielectric isolation mechanism that is recessed into the body below its upper surface so as to laterally separate a group of active portions of the body from one another and establishing an N-type connection region and a P-type connection region that extend from the upper surface respectively into a pair of the active portions;
• and
• causing the preceding dopants to diffuse further into the body during steps after the annealing step to form a heavily doped N-type buried region and a heavily doped P-type buried region that meet to define a PN junction whose entire perimeter adjoins the isolation mechanism below the upper surface of the body, the N-type regions meeting each other, the P-type regions meeting each other, the diode comprising the regions.