Self-assembled subnanolayers as interfacial adhesion enhancers and diffusion barriers for integrated circuits

Abstract

Preserving the structural and functional integrity of interfaces and inhibiting deleterious chemical interactions are critical for realizing devices with sub-50 nm thin films and nanoscale units. Here, we demonstrate that ∼0.7-nm-thick self-assembled monolayers (SAMs) comprising mercapto-propyl-tri-methoxy-silane (MPTMS) molecules enhance adhesion and inhibit Cu diffusion at Cu/SiO2 structures used in device metallization. Cu/SAM/SiO2/Si(001) structures show three times higher interface debond energy compared to Cu/SiO2 interfaces due to a strong chemical interaction between Cu and S termini of the MPTMS SAMs. This interaction immobilizes Cu at the Cu/SAM interface and results in a factor-of-4 increase in Cu-diffusion-induced failure times compared with that for structures without SAMs.

Atomistic fracture energy partitioning at a metal-ceramic interface using a nanomolecular monolayer

“…XPS spectra from Cu fracture surfaces show the Si 2p corelevel band at ~102.5 eV characteristic of silyl alkyl moieties in the organosilane, in contrast to the silica Si 2p signature at ~103.5 eV seen on silica fracture surfaces (see Fig. 3), confirming that delamination occurs via siloxane bond fissure at the NML-silica interface 10 . This delamination pathway remains characteristics are similar to, but consistently lower than, that from nanoindentation (Fig.…”

“…The Ta layer was used to offset poor Cu-epoxy adhesion. Our earlier works 9,10 have shown that the NML is strongly bound to the copper overlayer via thioligation and bond-breaking occurs exclusively at the NML-silica interface through the fissure of Si-O-Si bridges formed during molecular assembly (Fig. 1a).…”

“…NMLs were formed on Si (001) wafers capped with an 85-nm-thick silica by dipping the wafers in a 5 mM MPTMS in toluene for 30 min in flowing N 2 as described previously 9,10 . A 35-nm-thick Cu layer was deposited on the NML/SiO 2 /Si(001) followed by a 150-nm-thick Ta layer in a CVC DC sputter system with a 5 x 10 -7 Torr base pressure.…”

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

“…476 More recently, SAMS have been demonstrated as Cu diffusion barriers, [477][478][479] low-k ILD pore sealants, 480 Cu surface passivation layers, 481 and Cu/ILD adhesion promoters. 482,483 Due these successes and thicknesses <2-3 nm, SAMS are extremely attractive for meeting the ITRS forecast for <2 nm DBs. However in head-to-head comparisons with state-of-the-art TaN/Ta Cu diffusion barriers, SAMS have exhibited order of magnitude lower lifetimes in Cu-MIS TDDB testing indicating that SAMS may not be able to completely meet low-k/Cu interconnect reliability requirements.…”

Characterization of Chemical Vapor Deposited Copper Films on Mercaptan Self-Assembled Monolayer Diffusion Barriers

“…[3] As feature sizes decrease to below 100 nm, traditional interfacial barrier layers such as Ti/TiN and Ta/TaN are no longer suitable because they do not provide adequate performance as thicknesses reduce to 20 nm or less in order to maximize the space available for a copper conductor. [4] Recently, Ramanath et al [5,6] demonstrated the use of near-zero thickness (<2 nm thick) self-assembled molecular monolayers (SAMs) as candidates for ultrathin barrier layers to prevent Cu diffusion into SiO 2 -based dielectrics. They proposed that, due to its superior barrier property at the near-zero thickness, SAMs should be preferred over the traditional diffusion barriers of Ta, TaN, and TiN deposited onto Si/SiO 2 by conventional vapor deposition techniques.…”