Apparatus and method for electrical detection and localization of shorts in metal interconnect lines
View Patent ↗A test structure for localizing shorts in an integrated circuit and method of testing is described. A first comb structure is formed from a first busbar and a first plurality of fingers extending from the first busbar. A second comb structure formed from a second busbar and a second plurality of fingers extending from the second busbar. The second plurality of fingers is interleaved with the first plurality of fingers. A plurality of pass gates is connected between the first plurality of fingers and the first busbar. A pass gate terminal is electrically connected to the gate electrode of each of the plurality of pass gates. When the pass gates are turned OFF thereby disconnecting the first busbar from the first plurality of fingers, voltage contrast imaging can be used to identify which of the first fingers is adjacent the short.
1. A test structure for localizing defects leading to shorts in an integrated circuit, the test structure comprising:
a first pair of interleaved sets of fingers in a first region:
a second pair of interleaved sets of fingers in a second region;
a first busbar coupled to a first set of the first pair of interleaved sets of fingers and a first set of the second pair of interleaved sets of fingers;
a second busbar in the first region, wherein the second busbar is coupled connected to a second set of the first pair of interleaved sets of fingers;
a third busbar in the second region, wherein the third busbar is coupled to a second set of the second pair of interleaved sets of fingers;
a first series of pass gates in the first region, wherein the first series of pass gates selectively coupling one set of the first pair of interleaved sets of fingers; and
a second series of pass gates in the second region, wherein the second series of pass gates selectively coupling one set of the second pair of interleaved sets of fingers to one of the first and third busbars, respectively.
2. The test structure of claim 1 , wherein each of the first series of pass gates comprise a transistor.
3. The test structure of claim 1 , wherein:
the first busbar, the first set of the first pair of interleaved sets of fingers, and the first set of the second pair of interleaved fingers form a double comb structure.
4. The test structure of claim 1 , wherein the first series of pass gates is formed from a first plurality of transistors, wherein each of the first plurality of transistors comprise a gate electrode, and wherein the test structure further comprises:
a pass gate terminal electrically connected to each gate electrode of the first plurality of transistors.
5. The test structure of claim 1 , wherein:
the second series of pass gates is formed from a second plurality of transistors, wherein each of the second plurality of transistors comprise a gate electrode, and wherein the test structure further comprising a second pass gate terminal, and wherein the second pass gate terminal is electrically coupled to each gate electrode of the second plurality of transistors.
6. The test structure of claim 1 , wherein:
the first busbar is directly electrically connected to each finger of the first set of the first pair of interleaved sets of fingers in the first region;
the first busbar is directly electrically connected to each finger of the first set of fingers of the second pair of interleaved sets of fingers in the second region;
the first series of pass gates is coupled between the second busbar and the second set of the first pair of interleaved sets of fingers; and
the second series of pass gates is coupled between the third busbar and the second set of the second pair of interleaved sets of fingers.