Electromigration sign-off methodology

1. A method of performing electromigration sign-off, comprising:

determining an environmental temperature having a same value corresponding to a plurality of interconnect wires within a plurality of electrical networks of an integrated chip design;

determining a plurality of actual temperatures having different values corresponding to different ones of the plurality of interconnect wires, wherein the plurality of actual temperatures are respectively determined by adding the environmental temperature to a real temperature that accounts for Joule heating one of the plurality of interconnect wires;

determining an electromigration margin for a first interconnect wire within a first electrical network of the plurality of electrical networks, wherein the electromigration margin is determined at a first one of the plurality of actual temperatures corresponding to the first interconnect wire; and

comparing the electromigration margin to an electromigration metric, wherein the electromigration metric is an average current that is calculated as a function of the first one of the plurality of actual temperatures and a width of the first interconnect wire.

2. The method of claim 1 , wherein the real temperature is determined based upon a root mean square current on the one of the plurality of interconnect wires.

3. The method of claim 1 , wherein the real temperature is determined based upon heat generated by charge carriers within channel regions of one or more transistor devices within the integrated chip design.

4. The method of claim 1 , wherein a first real temperature corresponding to the first interconnect wire is determined based upon a contribution from charge carriers within a channel region of a transistor device within a second electrical network.

5. The method of claim 1 , further comprising:

increasing a width of the first interconnect wire if the electromigration metric is larger than the electromigration margin.

6. The method of claim 1 , further comprising:

determining a second electromigration margin for a second interconnect wire within a second electrical network of the plurality of electrical networks, wherein the second electromigration margin is determined at a second one of the plurality of actual temperatures corresponding to the second interconnect wire; and

comparing the second electromigration margin to a second electromigration metric.

7. The method of claim 1 , wherein determining the plurality of actual temperatures comprises:

determining a first actual temperature that accounts for Joule heating on the first interconnect wire;

determining a second actual temperature that accounts for Joule heating on a second interconnect wire within the first one of the plurality of electrical networks; and

wherein the first actual temperature is different than the second actual temperature.

8. A method of performing electromigration sign-off, comprising:

determining an environmental temperature having a same value for a first interconnect wire and a second interconnect wire;

determining a first real temperature for the first interconnect wire from a first RMS (root mean square) current on the first interconnect wire and determining a second real temperature for the second interconnect wire from a second RMS current on the second interconnect wire;

determining a first actual temperature that accounts for Joule heating on the first interconnect wire from the first real temperature and the environmental temperature;

determining a second actual temperature that accounts for Joule heating on the second interconnect wire from the second real temperature and the environmental temperature;

using the first actual temperature to determine a first average current limit that defines a first boundary on an average current in the first interconnect wire that is indicative of a first electromigration violation; and

comparing a first average current on the first interconnect wire to the first average current limit.

9. The method of claim 8 , further comprising:

using the second actual temperature to determine a second average current limit that defines a second boundary on an average current in the second interconnect wire that is indicative of a second electromigration violation; and

comparing a second average current on the second interconnect wire to the second average current limit.

10. The method of claim 8 , wherein the first interconnect wire is in a first electrical network and the second interconnect wire is in a second electrical network.

11. The method of claim 8 , wherein the first interconnect wire is electrically isolated from the second interconnect wire.

12. The method of claim 8 , further comprising:

increasing a width of the first interconnect wire if the first average current is larger than the first average current limit.

13. The method of claim 8 , further comprising:

decreasing a width of the first interconnect wire if the first average current is smaller than the first average current limit.

14. The method of claim 8 , wherein the first real temperature is different than the second real temperature.

15. A method of performing electromigration sign-off, comprising:

determining an environmental temperature having a same value for a plurality of interconnect wires;

determining a first real temperature of a first interconnect wire of the plurality of interconnect wires, wherein the first real temperature is determined by adding a change in temperature due to Joule heating on the first interconnect wire and a change in temperature due to heat generated by a transistor device below the first interconnect wire;

determining a first actual temperature corresponding to the first interconnect wire from the first real temperature and the environmental temperature;

using the first actual temperature to determine a first average current limit that defines a boundary on a numerical average of current in the first interconnect wire indicative of an electromigration violation; and

selectively adjusting a width of the first interconnect wire based on a comparison of a first average current on the first interconnect wire and the first average current limit.

16. The method of claim 15 , wherein the first real temperature is determined based upon a current on the first interconnect wire.

17. The method of claim 16 , wherein the first real temperature is determined based upon heat generated from charge carriers within channel regions of one or more transistor devices.

18. The method of claim 15 , wherein the plurality of interconnect wires are in a plurality of different electrical networks.

19. The method of claim 15 , wherein the first electromigration violation is present in the first interconnect wire if the first average current on the first interconnect wire is larger than the first average current limit.

20. The method of claim 8 , wherein comparing the first average current on the first interconnect wire to the first average current limit determines if the first electromigration violation is present in the first interconnect wire.