First-Principles Simulations of Conditions of Enhanced Adhesion Between Copper and TaN(111) Surfaces Using a Variety of Metallic Glue MaterialsThe work is supported by the National Natural Science Foundation of China (No. 20873127) and Air Products and Chemicals, Inc. (USA)

Particle aggregation and film agglomeration have been among the main technical hurdles for solid-state thin film development and have been observed in many semiconductor and catalytic systems. In heterogeneous catalysis, particle aggregation leads to reduction of effective surface area and degradation of catalytic performance. On semiconductor surfaces, film agglomeration may give rise to electric short, electron migration, and device degradation. Prevention of these effects presents a great technical challenge and has been one of the most active research areas in recent years. One approach towards reducing surface agglomeration is to insert a thin interfacial layer, often referred to as a “glue layer”, between the substrate and the adlayer of concern. Herein, we report three necessary fundamental conditions for a glue layer to be effective in promoting adhesion of a thin-film material to the substrate and to suppress agglomeration of the film at the interface. Copper agglomeration and adhesion enhancement on a TaN(111) surface, which was found to be the preferred orientation upon physical vapor deposition (PVD) growth, will serve as the model system to demonstrate the theoretical approach. Firstprinciples simulations were utilized to predict adhesion strength of various glue layer formulations. This approach allows us to make objective comparison of interaction energies between film interfaces and a set of performance criteria for material selection that augments empirically driven material selection processes, which have been largely trial-and-error in experiments to date. TaN has been used effectively as a barrier to prevent diffusion of the copper metal interconnect into the insulating dielectric and ultimately into the gate dielectric of CMOSbased transistors (CMOS= complementary metal oxide semiconductor). Atomic layer deposition (ALD) is a powerful thin-film deposition technique that provides atomistic control over deposition to support the continued scaling of the TaN barrier with a copper seed layer for advanced-generation CMOS devices. However, seed-layer copper agglomeration on the TaN surfaces has been a bottleneck in the development of this approach. Numerous attempts have been made to stabilize the copper thin film against agglomeration directly on the barrier with limited success. Recently, Kim et al. proposed to insert a thin ruthenium layer between the copper film and the TaN substrate to enhance copper adhesion. The concept was also demonstrated for a Cu/WN interfacial system. Unfortunately, a Ru-based process is expensive, and thus its applications are limited. Herein, we show that first-principles simulations are capable of providing quantitative information to aid material selection to allow broad applications of glue-layer-based technology using ALD. The TaN(111) surface is described by a slab model containing four alternating layers of tantalum and nitrogen, with nitrogen on top (Figure 1). In between slabs, there is a