Review of Graphene as a Solid State Diffusion Barrier

Abstract

Conventional thin-film diffusion barriers consist of 3D bulk films with high chemical and thermal stability. The purpose of the barrier material is to prevent intermixing or penetration from the two materials that encase it. Adhesion to both top and bottom materials is critical to the success of the barrier. Here, the effectiveness of a single atomic layer of graphene as a solid-state diffusion barrier for common metal schemes used in microelectronics is reviewed, and specific examples are discussed. Initial studies of electrical contacts to graphene show a distinct separation in behavior between metallic groups that strongly or weakly bond to it. The two basic classes of metal reactions with graphene are either physisorbed metals, which bond weakly with graphene, or chemisorbed metals, which bond strongly to graphene. For graphene diffusion barrier testing on Si substrates, an effective barrier can be achieved through the formation of a carbide layer with metals that are chemisorbed. For physisorbed metals, the barrier failure mechanism is loss of adhesion at the metal–graphene interface. A graphene layer encased between two metal layers, in certain cases, can increase the binding energy of both films with graphene, however, certain combinations of metal films are detrimental to the bonding with graphene. While the prospects for graphene's future as a solid-state diffusion barrier are positive, there are open questions, and areas for future research are discussed. A better understanding of the mechanisms which influence graphene's ability to be an effective diffusion barrier in microelectronic applications is required, and additional experiments are needed on a broader range of metals, as well as common metal stack contact structures used in microelectronic applications. The role of defects in the graphene is also a key area, since they will probably influence the barrier properties.

A long-term corrosion barrier with an insulating boron nitride monolayer

“…Graphene, an atomic-level thin layer, has been demonstrated as a corrosion barrier for metals including Ni, 2 Cu, [2][3][4][5] Ag, [6][7][8] Au 9 and Pt 10,11 and as a diffusion barrier for a metal-semiconductor interconnect. [12][13][14][15] Hightemperature annealing and electrochemical test showed excellent barrier performance of a graphene nanosheet for a short term. 2,[16][17][18] However, Zhou et al and Schriver et al revealed that a graphene barrier promotes the corrosion of Cu in air when the exposure time is extended to several months.…”

Oxidation behavior of graphene-coated copper at intrinsic graphene defects of different origins

“…Statistical observations suggest that various topological imperfections in graphene substantially degrade its properties 21 – 24 ; however, the study of the nature of intrinsic graphene defects and their influence on the physical and barrier properties of graphene are still in its infancy. Recently, several pioneering reports have demonstrated that engineered, polycrystalline graphene films can serve as effective diffusion 25 – 29 and oxidation 17 , 30 – 34 barriers for Cu. However, the literature contains extensive contradictory results, especially with respect to the effectiveness of graphene coatings as an oxidation barrier for Cu; the detailed mechanism by which Cu is oxidized through a polycrystalline graphene barrier remains a subject of debate 30 - 36 .…”

Sub‐Monolayer Growth of Titanium, Cobalt, and Palladium on Epitaxial Graphene

“…The contact between metal and graphene is also relevant for other processes like diffusion of metal atoms through the graphene sheet . This process is also activated when metals are intercalated in the interface between the epitaxial graphene layer and supporting SiC crystal …”