Patent ID: 7512506

Claim:
A method of performing a stress test of a line in an integrated circuit (IC) chip, the method comprising: applying a constant current I s to the line, wherein the applying the constant current to the line further comprises: determining a linear fit of an actual thermal resistance R th â€² of the line, wherein the linear fit determining includes: a) selecting a starting temperature T; b) calculating a power P based on an assumed thermal resistance R th ; c) calculating an electrical resistance R of the line from a temperature coefficient of resistance Î²; d) calculating and applying an initial current I for the line; e) calculating an actual power Pâ€² and a measured electrical resistance Râ€² based on a measured voltage Vâ€² and a measured current Iâ€²; f) calculating an actual temperature Tâ€² based on the measured electrical resistance Râ€²; g) incrementing the actual temperature T by a small value; h) repeating processes b) through g) a number of times sufficient for a linear regression calculation to be performed for the thermal resistance R th ; i) calculating an actual thermal resistance R th â€² based on the actual temperature Tâ€², a probe temperature T chuck and the actual power Pâ€² by performing a linear regression for the actual thermal resistance R th â€²; and asymptotically ramping a temperature of the line to a predetermined target stress temperature T s based on the actual thermal resistance R th â€², the asymptotic temperature ramping caused by an applied current to ramp asymptotically, wherein the asymptotic temperature ramping includes: j) incrementing to a next required current I A such that a next temperature T n moves toward the predetermined target stress temperature T s in an asymptotic manner; k) calculating an actual power P A â€² for the next temperature T n based on the actual thermal resistance R th â€²; l) calculating and applying a required current I A based on the actual power P A â€² and the actual electrical resistance Râ€²; m) calculating an actual power Pâ€² and an actual electrical resistance Râ€² based on a measured voltage Vâ€² and a measured current Iâ€²; n) calculating the actual temperature Tâ€² based on a measured electrical resistance Râ€²; o) calculating the actual thermal resistance R th â€² based on the actual temperature Tâ€², the probe temperature T chuck and the actual power Pâ€²; p) determining whether the actual temperature Tâ€² is within a threshold of the predetermined target stress temperature T s ; and q) repeating processes k) through p) in the case that the actual temperature Tâ€² is not within the threshold of the predetermined target stress temperature T s , and, otherwise, setting the constant current I s for the line as the required current I A for the stress testing; and stress testing the line while applying the constant current I s , wherein the constant current I s is not altered by a resistance change due to an onset of electromigration.