ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Electrical resistance of Al-1 wt % Si thin-film conductors has been measured as a function of time t, temperature, and current polarity in order to investigate both generation and recovery of (microstructural) damage caused by electromigration. The fractional change of electrical resistance ΔR/R is characterized by three distinct stages: (i) undetectable ΔR/R during an incubation period τ; (ii) linear increase of ΔR/R with t−τ; and (iii) abrupt decrease of ΔR/R when polarity is reversed, followed by gradual resumption of the previous linear increase. Examination of the conductor surface during these three stages by scanning electron microscopy reveals: (i) undetectable microstructural damage; (ii) generation of (first) holes and (then) hillocks; and (iii) recovery followed by further generation of microstructural damage. Results are interpreted by (i) generation of stress σ in grain boundaries; (ii) formation of holes when σ exceeds a critical tensile stress σ+c and hillocks when σ exceeds a critical compressive stress σ−c (||σ+c|| 〈 ||σ−c||), and (iii) interchange of tensile and compressive stress by polarity reversal. The last stage, in fact, represents superposition of a continuation of the linear increase (degradation) of ΔR/R due to the applied current and an exponential decrease (healing) of ΔR/R, characterized by τ, due to stress relaxation. In general, damage and subsequent healing by electromigration involve a delicate balance between applied current, time, and spatial distribution of (elastic) tensile and compressive stress, (anelastic) formation of holes, and (plastic) formation of hillocks, as dictated by the concomitant microstructure.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.351653
