Self-Assembled Monolayers as Cu Diffusion Barriers for Ultralow-k Dielectrics

Abstract

Ultralow-k dielectrics are mainly porous and pose reliability issues as copper barrier integrity is compromised on porous surfaces. No work is reported on use of self-assembled monolayers ͑SAMs͒ as Cu diffusion barrier or to seal pores for ultralow-k dielectrics. We attached SAMs to ultralow-k film and confirmed by analytical techniques such as Auger and X-ray photoelectron spectroscopic analysis. We report reduction of leakage current and enhancement of dielectric breakdown voltage of the ultralow-k p-SiLK film after SAM attachment showing it to be a promising barrier material for prevention of Cu diffusion. H 2 /N 2 plasma treated p-SiLK film showed early breakdown and high leakage in spite of SAM attachment. .As the feature size further shrinks for 65 nm and below technology nodes for advanced Cu interconnects, ultrathin-barrier layers are needed and further improvement of step coverage is necessary. In the efforts to prevent Cu diffusion, it becomes challenging to meet the requirements of realizing sub-10 nm barrier layers. An alternative approach of self-assembled monolayers ͑SAMs͒ as barrier layers has been recently explored and studied. 1 The main advantage of the SAM is its "near zero" thickness which is just one molecular length. This is attractive for future technologies that will require nano-sized interconnects. 2 The molecules of SAM are composed of three parts, the terminal functional group, the alkyl chain, and the anchor group. SAMs are typically attached to a substrate on one end by moieties such as a thiol ͑-SH͒ anchor groups. The other end is usually comprised of a silane ͑-SiX3͒ where X is typically a halogen or an alkoxy group͒. The feasibility of employing SAM as a diffusion barrier for Cu/oxide interconnects was first reported by Ramanath et al. 3 All subsequent studies by other researchers reported the diffusion barrier property of SAM coated on SiO 2 with dielectric constant k = ϳ 4. No report is found for the effect of SAM on new generation materials such as ultralow-k dielectrics, which are being used to further reduce the interconnect RC delay.In this study, we have used a porous ultralow-k material namely p-SiLK ͑from The Dow Chemical͒ which is an aromatic carbon rich organic polymer, with a k value of 2.2. 4 The low dielectric constant in this material is achieved by introducing nano-pores into the bulk. Porosity related issues such as moisture or solvent absorption, enhanced Cu diffusion, and poor barrier integrity are huge concerns in Cu damascene process integration. Many methods have been tried to seal the pores, one such is to deposit by physical vapor deposition of an ultrathin dielectric layer as barrier to prevent Cu diffusion. 5 In this case, there is no chemical bonding between the dielectric and Cu. SAM is a single molecule of length ϳ20 Å, thereby satisfying thickness requirements and is attached to both Cu and dielectric by chemical bonds. The formation of chemical bond could in turn help to improve dielectric and metallization reliability.The p-SiLK material was spun o...

Electrochemical studies of self-assembled monolayers using impedance spectroscopy

“…In general, surface functionalization using SAMs is a wide field of research with various micro-technologies applications such as corrosion protection [4], adhesion promotion [5,6], diffusion barriers formation [7] and also for bio-and non-bio-molecular sensing applications [8]. Recently, surface functionality has been demonstrated by using two kinds of chemistries forming the SAM with different properties on different places on the same chip.…”

Molecular junctions of ∼1 nm device length on self-assembled monolayer modified n- vs. p-GaAs

“…The deposition of metallic overlayers on insulating organic selfassembled monolayers (SAMs) is of great significance to various research areas including the formation of electrical contacts in molecular electronics, 1 fabrication of electromigration barrier layers for interconnects within nanoelectronics, [2][3][4] and the formation of metallic clusters 5 for localization of plasmonic effects. 6 For contact formation purposes in molecular electronics and barrier layer fabrication for nanoelectronics, the deposition and patterning of metallic layers that do not penetrate through the SAM layer is required, in order to avoid electrical shorts, growth of metallic filaments, and electromigration.…”

Formation of Organic Nanoscale Laminates and Blends by Molecular Layer Deposition

“…For example, covalently bound organic self-assembled monolayers have been employed as interfacial layers between substrates and organic semiconductors to aid in film ordering, − and also used as the organic semiconductor layer, in organic thin film transistors. , Organic films are also used in chemical sensors, and as wires and dielectrics in molecular electronics. − Recently, interest has grown in using nanoscale organic films to replace more conventional materials in silicon-based electronics as approaching atomic dimensions puts severe limitations on materials properties. Already, organic films have shown promise as copper diffusion barriers and liners for interconnect processing, − and it is likely that nanoscale organic films will receive more attention in the future as alternatives to current photoresists as lithography exposure wavelengths are pushed smaller and smaller.…”