IC structure with interdigitated conductive elements between metal guard structures

An integrated circuit (IC) structure, comprising:

• a back end of line (BEOL) stack on a substrate, the BEOL stack having a plurality of metal layers therein and a plurality of inter-level dielectric (ILD) layers therein, wherein the plurality of metal layers includes a lowermost metal layer an uppermost metal layer, and at least one sensor layer between the lowermost metal layer and the uppermost metal layer;
• active circuitry coupled to at least one of the plurality of metal layers of the BEOL stack;
• a first metal guard structure positioned between the active circuitry and an outer perimeter of the BEOL stack, wherein the first metal guard structure includes a first continuous metal fill between the lowermost metal layer and the uppermost metal layer of the plurality of metal layers;
• a second metal guard structure between the active circuitry and the first metal guard structure, and separated from the first metal guard structure by a separation distance, the second metal guard structure concentrically surrounding the active circuitry, wherein the second metal guard structure includes a second continuous metal fill between the lowermost metal layer and the uppermost metal layer of the plurality of metal layers;
• a first plurality of conductive teeth within the at least one sensor layer and extending horizontally from the first metal guard structure toward the second metal guard structure without contacting the second metal guard structure;
• and
• a second plurality of conductive teeth within the at least one sensor layer and extending horizontally from the second metal guard structure toward the first metal guard structure without contacting the first metal guard structure, the second plurality of conductive teeth interdigitating with the first plurality of conductive teeth.

A method for monitoring an integrated circuit (IC) structure, the method comprising:

• applying a voltage to a pair of metal guard structures within a back end of line (BEOL) stack having a plurality of metal layers,
• wherein each metal guard structure includes a continuous metal fill between a lowermost metal layer and a uppermost metal layer of the plurality of metal layers, and
• wherein the pair of metal guard structures includes a set of interdigitating conductive elements within one of the plurality of metal layers, the set of interdigitating conductive elements including a first plurality of conductive elements electrically coupled to one of the pair of metal guard structures interdigitating with a second plurality of conductive elements electrically coupled to the other of the pair of metal guard structures;
• measuring a test current or capacitance through the pair of metal guard structures based on the applied voltage;
• calculating a differential current or capacitance between the test current or capacitance and a reference value for the pair of metal guard structures;
• in response to the differential current or capacitance not exceeding a threshold, repeating the transmitting and calculating;
• and
• in response to the differential current or capacitance exceeding the threshold, transmitting a signal to active circuitry of the IC structure to indicate current leakage through the pair of metal guard structures.