Electromigration in Cu(Al) and Cu(Mn) damascene lines

Abstract

The effects of impurities, Mn or Al, on interface and grain boundary electromigration (EM) in Cu damascene lines were investigated. The addition of Mn or Al solute caused a reduction in diffusivity at the Cu/dielectric cap interface and the EM activation energies for both Cu-alloys were found to increase by about 0.2 eV as compared to pure Cu. Mn mitigated and Al enhanced Cu grain boundary diffusion; however, no significant mitigation in Cu grain boundary diffusion was observed in low Mn concentration samples. The activation energies for Cu grain boundary diffusion were found to be 0.74 ± 0.05 eV and 0.77 ± 0.05 eV for 1.5 μm wide polycrystalline lines with pure Cu and Cu (0.5 at. % Mn) seeds, respectively. The effective charge number in Cu grain boundaries Z*GB was estimated from drift velocity and was found to be about −0.4. A significant enhancement in EM lifetimes for Cu(Al) or low Mn concentration bamboo-polycrystalline and near-bamboo grain structures was observed but not for polycrystalline-only alloy lines. These results indicated that the existence of bamboo grains in bamboo-polycrystalline lines played a critical role in slowing down the EM-induced void growth rate. The bamboo grains act as Cu diffusion blocking boundaries for grain boundary mass flow, thus generating a mechanical stress-induced back flow counterbalancing the EM force, which is the equality known as the “Blech short length effect.”

Dielectric Barrier, Etch Stop, and Metal Capping Materials for State of the Art and beyond Metal Interconnects

“…[376][377][378][379][380][381][382][383] Numerous different types of dopants elements beyond Si have been reported for Cu with Sn, Al, Mg, and Mn being perhaps the most popular. In this method, the improvements in electromigration are believed to be due to the dopant atom segregating from the bulk Cu and diffusing to the Cu/DB interface and helping passivate the Cu surface and/or improving the adhesion strength between Cu and the DB.…”

“…Many of the reported methods involve either doping the Cu lines with a few percent of select alloying elements, [376][377][378][379][380][381][382] or selectively forming an additional surface passivation layer material between the DB and Cu. [383][384][385][386][387][388][389][390][391][392][393] In most cases, these methods involve additional processing steps separate from the DB deposition process.…”

Assessment of minority-alloy component segregation (e.g. Mn, Al) in back end of line copper trench structures using Kelvin probe technique

“…SIMS is the only technique that can provide a quantitative measure of alloy segregation in the lines but is still a complex, small-area technique that is mostly performed off-line. Electromigration, another measure of alloy segregation, can be performed only after far back-end of line build [2,3]. It would be very beneficial to have a screening in-line measurement full-wafer technique that can screen out wafers that have little or no alloy segregation or huge variation across the wafer to help minimize the number of reliability parts for stressing.…”

“…1(c) shows the absence of Mn segregation at the top of a trench, because of insufficient oxygen barrier provided by the barrier layer and oxygen sites from the dielectric being available to Mn to bond. It is also known that the Cu grain structure in the trenches is a common factor affecting the Mn segregation in lines [ 2].…”

Manganese Segregation Behavior in Damascene Metal Lines

“…Even though the doping level (less than fractions of a percent) is below physical detection limits by analytical transmission electron microscopy (TEM) techniques, the improvement of EM is observed by electrical test [1]. However after thermal stress or reliability tests, Mn segregates to the interfaces and GB at a higher concentration than in bulk Cu which makes it in the detectable range using an advanced analytical TEM technique on ultrathin lamella prepared with inverted dual beam focus ion beam (FIB).…”