Influence of a Capping Layer on the Mechanical Properties of Copper Films

Abstract

The substrate curvature technique was employed to study the mechanical properties of 0.6 ýtm and 1.0 jim Cu films capped with a 50 nm thick Si 3 N 4 layer and to compare them with the mechanical properties of uncapped Cu films. The microstructures of these films were also investigated. Grain growth, diffusional creep and dislocation processes are impeded by the cap layer. This is evident in the form of high stresses at high temperatures on heating and at low temperatures on cooling. At intermediate temperatures on heating and cooling, stress plateaus a relatively low stresses exist. This can be explained by the so-called Bauschinger effect. A film thickness dependence of the stresses in the film could not be observed for capped Cu films.

Influence of Film Thickness and Capping Layer on the Mechanical Properties of Copper Films

“…The capped Cu films exhibit a stronger (111) texture in the a.d. state than the uncapped films. This may be due to grain growth during deposition of the Si 3 N 4 capping layer [9], which is supported by the bigger a.d. grain sizes of the capped films. Texture sharpens after annealing with a constant (100) component as observed for the 0.6 Cu films without a capping layer.…”

“…At 250 0 C the stress increases rapidly and reaches a higher RT stress than the uncapped 1 gtm Cu film. No thickness dependence exists [9]. On heating in the second cycle the a-T-curve deviates from the thermo-elastic line at a lower temperature (120 0 C) and a long stress plateau at very low compressive stress level continues up to 400'C where the stress starts to increase and reaches the stress value of the first cycle.…”

“…The capped films have same plateaus at same temperatures but then display an increase in both stress and dislocation density at higher temperatures. We have previously explained a-T behavior of capped films in terms of a dislocation mechanism [9]. We proposed, that internal stress is created as dislocations pile up at obstacles during the first half of a cycle.…”