Samarium influence on current induced atomic displacement in Aluminium and Copper combinatorial thin film alloys

Abstract

Combinatorial thin film deposition from vapor phase combined with photolithography was involved in preparation of bidimensional wires for electromigration testing along Al-Cu, Al-Sm and Cu-Sm thin film libraries. Samarium was chosen as alloying element due to its larger atomic radius, directly impacting the crystallographic properties of the conducting alloy and decreasing the total grain boundary surface through amorphisation. As reference, pure Al and Cu wires were additionally deposited and studied. Empirical estimation of the experimental errors obtained during electromigration testing was performed by high throughput measurements and a value around 2% was found for pure Al and Cu metals. The resistance against electromigration of test wires was increased by electrochemical passivation (leading to void pinning), while the empirically evaluated experimental errors increased to 30%. Electrical screening of Al and Cu-based thin film combinatorial libraries was performed at extremely high current densities (MA cm−2). In the Al-Cu system, Al–14 at.% Cu was identified as the alloy able to withstand the highest power density of 2.10 MW cm−2 before failure. The Al-Sm and Cu-Sm thin film libraries showed compositional regions of total or partial amorphization likely impacting the electromigration resistance of the alloys. Electrical screening indicated that Al-6 at.% Sm is the alloy withstanding the highest power density before failure with a value of 2.48 MW cm−2. The highest current densities before electrical failure in conducting lines were measured on pure Al at 1.39 MA cm−2, with a value of maximum power density below 2.62 MW cm−2. Careful discrimination between these two variables is necessary before choosing one of the studied materials as ideal for specific applications.