Integrated circuit having stress migration test structure and method therefor
First Claim
1. An integrated circuit, comprising:
- a substrate having circuits fabricated thereon, the circuits connected to leads of the integrated circuit;
a stress migration test device fabricated on the substrate, the stress migration test device comprising a conductive runner, the conductive runner having a length sufficient to develop axial stress above the threshold for nucleating voids for the technology in which the runner is fabricated, the conductive runner having a plurality of taps at uniform impedance intervals along the runner, the taps spaced along the runner such that the variation of impedance of the runner between adjacent taps due to presence of a stress migration void in the conductive runner is a detectable portion of the impedance between the adjacent taps absent stress migration voids;
a constant current source coupled to the stress migration test device for driving a known current into the conductive runner;
a plurality of switches capable of providing selected ones of the taps to first and second output nodes; and
a control circuit for controlling the state of the plurality of switches to couple selected ones of the taps to the first and second output nodes.
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Accused Products
Abstract
A stress migration test structure is provided that can be used to detect stress migration defects in traces or conductors of integrated circuits. The stress migration test structure can be placed between die areas on a wafer, or on a die. On the die, a stress migration test structure can be placed in otherwise unused areas of a die such as between bond pads and the periphery of a die, in a layer beneath bond pads, in a region between the bond pads and the perimeter of standard area for circuit layout, or in regions in more than one level of the integrated circuit. The stress migration test structure may also be placed within the standard area for circuit layout and used, with some additional circuitry, as a stress migration test structure on an integrated circuit once the die is packaged. Obtaining information from the impedance segments of a stress migration test structure can be accomplished employing either a mechanical stepping or an electrical stepping technique.
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Citations
36 Claims
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1. An integrated circuit, comprising:
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a substrate having circuits fabricated thereon, the circuits connected to leads of the integrated circuit;
a stress migration test device fabricated on the substrate, the stress migration test device comprising a conductive runner, the conductive runner having a length sufficient to develop axial stress above the threshold for nucleating voids for the technology in which the runner is fabricated, the conductive runner having a plurality of taps at uniform impedance intervals along the runner, the taps spaced along the runner such that the variation of impedance of the runner between adjacent taps due to presence of a stress migration void in the conductive runner is a detectable portion of the impedance between the adjacent taps absent stress migration voids;
a constant current source coupled to the stress migration test device for driving a known current into the conductive runner;
a plurality of switches capable of providing selected ones of the taps to first and second output nodes; and
a control circuit for controlling the state of the plurality of switches to couple selected ones of the taps to the first and second output nodes. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A method for determining the presence or absence of stress migration voids in a conductor of an integrated circuit, comprising the steps of:
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fabricating on a substrate a conductive runner having a length sufficient to develop axial stress above the threshold for nucleating voids for the technology in which the runner is fabricated;
providing taps at equal impedance intervals along the runner, the conductive runner between two taps defining a section of the conductive runner;
passing a known current through the conductive runner;
coupling selected ones of the taps to first and second leads of the integrated circuit;
measuring the voltage developed between the selected taps at the first and second leads;
calculating an impedance of the section of the conductive runner between the selected taps;
normalizing the impedance of the section of the conductive runner between the selected taps by a nominal impedance to generate an impedance ratio; and
comparing the impedance ratio to an impedance ratio threshold to determine whether a stress migration void is present in the section of the conductive runner between the selected taps. - View Dependent Claims (19, 20, 21, 22)
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23. A method for determining the presence or absence of stress migration voids in a conductor of an integrated circuit, comprising the steps of:
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fabricating on a substrate a conductive runner having a length sufficient to develop axial stress above the threshold for nucleating voids for the technology in which the runner is fabricated;
providing taps at impedance intervals along the runner, the conductive runner between two taps defining a section of the conductive runner;
passing a known current through the conductive runner;
coupling selected ones of the taps to first and second leads of the integrated circuit;
measuring the voltage developed between the selected taps at the first and second leads;
calculating an impedance of the section of the conductive runner between the selected taps;
normalizing the impedance of the section of the conductive runner between the selected taps by an expected impedance for the conductive runner between the selected taps to generate an impedance ratio; and
comparing the impedance ratio to an impedance threshold to determine whether a stress migration void is present in the section of the conductive runner between the selected taps. - View Dependent Claims (24, 25, 26, 27, 28)
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29. An integrated circuit, comprising:
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a substrate having circuis fabricated thereon, the circuits connected to leads of the integrated circuit;
a stress migration test device fabricated on the substrate, the stress migration test device comprising a conductive runner, the conductive runner having a length sufficient to develop axial stress above the threshold for nucleating voids for the technology in which the runner is fabricated, the conductive runner having a plurality of taps in uniform impedance intervals along the runner, the taps spaced along the runner such that the variation of impedance of the runner between adjacent taps due to presence of a stress migration void in the conductive runner is a detectable portion of the impedance between the adjacent taps absent stress migration voids;
a constant current source coupled to the stress migration test device for driving a known current into the conductive runner;
a plurality of switches capable of providing selected ones of the taps to an output node; and
a control circuit for controlling the state of the plurality of switches to sequentially couple one of the selected taps to the output node. - View Dependent Claims (30, 31, 32)
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33. A method for determining the presence or absence of stress migration voids in a conductor of an integrated circuit, comprising the steps of:
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fabricating on a substrate a conductive runner having a length sufficient to develop axial stress above the threshold for nucleating voids for the technology in which the runner is fabricated;
providing taps at equal impedance intervals along the runner, the conductive runner between two taps defining a section of the conductive runner;
passing a known current through the conductive runner;
coupling a selected one of the taps to a lead of the integrated circuit;
measuring the voltage developed between the selected tap at the lead and a reference;
indexing the selected tap coupled to the lead of the integrated circuit to couple an adjacent tap to the lead of the integrated circuit;
measuring the voltage developed between the indexed tap and the reference;
calculating an impedance of the section of the conductive runner between the adjacent taps;
normalizing the impedance of the section of the conductive runner between the adjacent taps by a nominal impedance to generate an impedance ratio; and
comparing the impedance ratio to an impedance ratio threshold to determine whether a stress migration void is present in the sections of the conductive runner between the adjacent taps. - View Dependent Claims (34, 35, 36)
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Specification