Binary Cu-alloy layers for Cu-interconnections reliability improvement

Abstract

This paper discusses applications of thin dilute Cu-alloy films in Cu-interconnections to reduce Cu electromigration (EM) and improve physical-vapor-deposited (PVD) Cu seed integrity. PVD CuSn, CuIn and CuZr films are studied with in-film concentration of Sn, In and Zr from 0.3 to 1.2 at. %. With either of the alloy films, significant reduction of thin Cu film agglomeration on TaN barrier is observed, suggesting suppression of Cu mobility along the Cu/barrier interface, which thus reduces EM. After annealing, the dopant redistribution rate is found in the order of Sn> In> Zr. The bulk resistivity differences between as-deposited Cu-alloy and pure Cu films are 3.6, 1.1 and 18 pLR-cm for CuSn, CuIn and C U B , respectively (normalized to 1 at. %). The resistance decreases 30-50% after annealing due to the dopant rejection from the grains. CuSn (0.3 at. %) is discussed as a specific example to correlate film propertie"'with wafer-level electrical and EM results. When annealed at 35OoC, Cu-interconnect lines with 500A (nominal thickness) CuSn films have similar metal line resistance to that of pure Cu. EM mean-time-tofailure (MTTF) improves with increasing CuSn film thickness. A 1kA CuSn film improves EM by a factor of two.

Process options for improving electromigration performance in 32nm technology and beyond

“…Finally metal alloying is another possible approach to fulfill EM requirements without degrading ILD breakdown strength [8]. Cu-alloy usually has much higher line resistances than the In other words process development at these dimensions always ends up in the trade-off between electromigration (EM) performance, dielectric breakdown strength (BTS) and resistance increase.…”

Comparison of Lifetime Improvements in Electromigration between Ti Barrier Metal and Chemical Vapor Deposition Co Capping

“…2) Cu alloy interconnects are fabricated by doping impurities from a Cu alloy seed layer or a barrier metal layer. As a seed layer, CuAl, [3][4][5] CuMn, 6,7) and CuSn 8,9) have been used, whereas as a barrier metal layer, Ti-based layers 10,11) have been used. For metal capping on Cu interconnects, Co-based cap metals have been studied frequently, which were deposited by selective electroless plating.…”

A 3 nm Self-Forming InOx Diffusion Barrier for Advanced Cu/Porous Low-k Interconnects

“…Previous investigations indicated that the addition of elements, such as Pd, Sn, and Ti, into the Cu line can improve the EM lifetime for enhanced reliability. 6,7) Copper alloys, such as Cu-Al, Cu-Mg, and Cu-Ti, serving as copper seed layers and barriers have been reported. [8][9][10] Recently, self-forming diffusion barriers [11][12][13] have demonstrated great potential in meeting all ITRS requirements.…”