The Effect of Cu Alloying on Al Alloy Thin Films: Microstructural Mechanisms That Enhance Electromigration Resistance

AbstractThe microstructural evolution of unpatterned Al-2wt.%Cu thin films has been examined to elucidate the mechanism by which copper improves electromigration resistance. After annealing at 425°C and cooling to room temperature at a rate of approximately 1°C/min., the microstructure of the Al-Cu films consisted of 1 μm aluminum grains with θ-phase Al2Cu precipitates at grain boundaries and triple points. The grain size and precipitation distribution did not change with subsequent isothermal heat treatments in the temperature range of 200° to 400°C. Al-Cu thin films annealed at 400°C, a temperature just below the Al/Al+θ solvus, exhibited microstructures in which the aluminum grain boundaries were depleted in copper except for the presence of the pre-existing large, widely dispersed AI2Cu precipitates. Al-Cu thin films annealed at 200° to 300°C were enriched with copper at the aluminum grain boundaries. The large, widely dispersed Al2Cu precipitates remained after the lower temperature anneals. From these results, it is proposed that the presence of copper in aluminum thin films improves electromigration resistance due to the precipitation of a thin film of Al2Cu, or a substoichiometric precursor, along the grain boundaries. The grain boundary phase retards grain boundary diffusion in the thin films, thereby reducing total mass transport and improving electromigration resistance.

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Constrained Grain Boundary Diffusion In Thin Copper Films

MRS Proceedings ◽

10.1557/proc-821-p1.2 ◽

2004 ◽

Vol 821 ◽

Cited By ~ 4

Author(s):

Markus J. Buehler ◽

Alexander Hartmaier ◽

Huajian Gao

Keyword(s):

Thin Films ◽

Theoretical Analysis ◽

Grain Boundary ◽

Grain Boundaries ◽

Boundary Diffusion ◽

Grain Boundary Diffusion ◽

Atomic Scale ◽

Diffusional Creep ◽

Copper Films ◽

And Diffusion

AbstractIn a recent study of diffusional creep in polycrystalline thin films deposited on substrates, we have discovered a new class of defects called the grain boundary diffusion wedges (Gao et al., Acta Mat. 47, pp. 2865-2878, 1999). These diffusion wedges are formed by stress driven mass transport between the free surface of the film and the grain boundaries during the process of substrate-constrained grain boundary diffusion. The mathematical modeling involves solution of integro-differential equations representing a strong coupling between elasticity and diffusion. The solution can be decomposed into diffusional eigenmodes reminiscent of crack-like opening displacement along the grain boundary which leads to a singular stress field at the root of the grain boundary. We find that the theoretical analysis successfully explains the difference between the mechanical behaviors of passivated and unpassivated copper films during thermal cycling on a silicon substrate. An important implication of our theoretical analysis is that dislocations with Burgers vector parallel to the interface can be nucleated at the root of the grain boundary. This is a new dislocation mechanism in thin films which contrasts to the well known Mathews-Freund-Nix mechanism of threading dislocation propagation. Recent TEM experiments at the Max Planck Institute for Metals Research have shown that, while threading dislocations dominate in passivated metal films, parallel glide dislocations begin to dominate in unpassivated copper films with thickness below 400 nm. This is consistent with our theoretical predictions. We have developed large scale molecular dynamics simulations of grain boundary diffusion wedges to clarify the nucleation mechanisms of parallel glide in thin films. Such atomic scale simulations of thin film diffusion not only show results which are consistent with both continuum theoretical and experimental studies, but also revealed the atomic processes of dislocation nucleation, climb, glide and storage in grain boundaries. The study should have far reaching implications for modeling deformation and diffusion in micro- and nanostructured materials.

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Kinetics of Cu Segregation in Al-Cu(1at% Cu) Interconnects Studied by Resistance Measurements

MRS Proceedings ◽

10.1557/proc-473-267 ◽

1997 ◽

Vol 473 ◽

Cited By ~ 4

Author(s):

A. J. Kalkman ◽

A. H. Verbruggen ◽

G. C. A. M. Janssen ◽

S. Radelaar

Keyword(s):

Thin Films ◽

Activation Energy ◽

Grain Boundary ◽

Room Temperature ◽

Boundary Diffusion ◽

Measurement Temperature ◽

Temperature Range ◽

Different Temperatures ◽

Resistance Decrease ◽

Kinetics Of

ABSTRACTThe time-dependence of the growth of Al2Cu precipitates in Al-Cu(lat% Cu) thin films is studied by means of resistance measurements at different temperatures. The samples are annealed at 400°C for 1 hour, and then quickly cooled down to room temperature. Afterwards, the samples are heated within one minute to a measurement temperature between 140 °C and 240 °C. Growth of precipitates causes a well defined decrease in resistance. The observed resistance decrease does not follow an exponential decay. In the investigated temperature range the resistance decrease can be accurately modelled by (R(t)-R∞) = (Ro-R∞)exp(-(t /τ)n), with the time constant τ= τ0 exp(Ea / kT). Excellent fits were obtained resulting in n = 0.66±0.05, independent of temperature, and Ea= 0.81±0.03 eV. This value for the activation energy agrees very well with the activation energy that has been reported in literature for both electromigration failure in Al-Cu and grain-boundary diffusion of Cu in Al. The value we found for n is intriguingly close to 2/3 and deviates strongly from the values of n reported for bulk Al-Cu (n = 1.5–1.8) in the same temperature range.

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Grain‐boundary diffusion in thin films. II. Multiple grain boundaries and surface diffusion

Journal of Applied Physics ◽

10.1063/1.322441 ◽

1976 ◽

Vol 47 (10) ◽

pp. 4373-4380 ◽

Cited By ~ 64

Author(s):

G. H. Gilmer ◽

H. H. Farrell

Keyword(s):

Thin Films ◽

Grain Boundary ◽

Grain Boundaries ◽

Surface Diffusion ◽

Boundary Diffusion ◽

Grain Boundary Diffusion

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Characterization of intergranular cuprous oxide in polycrystalline YBa2Cu3O7-x

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100106466 ◽

1988 ◽

Vol 46 ◽

pp. 880-881

Author(s):

Bradley L. Thiel ◽

Chan Han R. P. ◽

Kurosky L. C. Hutter ◽

I. A. Aksay ◽

Mehmet Sarikaya

Keyword(s):

Grain Boundary ◽

Cuprous Oxide ◽

Room Temperature ◽

Boundary Phase ◽

Spectroscopic Techniques ◽

Transition Width ◽

Practical Applications ◽

Thin Foils ◽

Superconducting Oxides

The identification of extraneous phases is important in understanding of high Tc superconducting oxides. The spectroscopic techniques commonly used in determining the origin of superconductivity (such as RAMAN, XPS, AES, and EXAFS) are surface-sensitive. Hence a grain boundary phase several nanometers thick could produce irrelevant spectroscopic results and cause erroneous conclusions. The intergranular phases present a major technological consideration for practical applications. In this communication we report the identification of a Cu2O grain boundary phase which forms during the sintering of YBa2Cu3O7-x (1:2:3 compound).Samples are prepared using a mixture of Y2O3. CuO, and BaO2 powders dispersed in ethanol for complete mixing. The pellets pressed at 20,000 psi are heated to 950°C at a rate of 5°C per min, held for 1 hr, and cooled at 1°C per min to room temperature. The samples show a Tc of 91K with a transition width of 2K. In order to prevent damage, a low temperature stage is used in milling to prepare thin foils which are then observed, using a liquid nitrogen holder, in a Philips 430T at 300 kV.

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