Fundamentals of Cu/Barrier-Layer Adhesion in Microelectronic Processing
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Fundamentals of Cu/Barrier-Layer Adhesion in Microelectronic Processing Harsono Simka1, Sadasivan Shankar1, Carolyn Duran2, and Michael Haverty1 1 Technology CAD Department – Logic Technology Development, 2 Storage Technologies Group, Technology and Manufacturing Group, Intel Corporation, 2200 Mission College Blvd., SC12-205, Santa Clara, CA 95052, U.S.A.
ABSTRACT Copper is most widely used interconnect material in present silicon microelectronic technologies. As such, multiple interfaces formed by a thin Cu layer and other materials must be engineered to achieve the desired chemical, mechanical, and electrical properties. Adhesion between Cu and the barrier layer, as well as between Cu and the dielectric, is of particular interest, due to its role in controlling interfacial stability and Cu electromigration behavior [1]. This work focuses on understanding how the interface chemistry affects adhesion. Firstprinciples density functional theory (DFT) calculations were used to determine chemical adhesion energies of interfaces formed by Cu and various metals considered as a diffusion barrier, including Ta, TiN, and W. Calculations predicted increasing adhesion strength in the order of TiN < Si-doped TiN < TaN < Ta, consistent with wetting experiments done using 100Å thick Cu layer samples. The effects of doping at the interface using light elements (C, N, O) were also determined. Calculations were also done for interfaces of Cu with two different classes of amorphous dielectric materials, i.e. silicon nitride and silicon carbide, for which detailed material characterizations are often difficult and time consuming. Calculations predicted Cu/Si-nitride and Cu/Si-carbide adhesion strengths consistent with 4-pt-bend experiments, including the improvement in adhesion energies when silicon was used to dope the interface. In addition, weaker interfaces provide low-resistance diffusion paths for Cu atoms during electromigration. The first-principles based modeling, validated by select adhesion measurements, provides a predictive approach to effectively determine adhesion strengths and predict electromigration reliability in interconnects.
INTRODUCTION The use of new materials, such as copper interconnect and transition metal barrier layer materials in sub-micron semiconductor devices, requires development of copper/barrier-layer interfaces that are stable and have good adhesion properties. In addition to being a good barrier to copper diffusion, the barrier-layer should prevent undesired reactions at the copper/barrierlayer interface. Experimentally based material development of these stacks is expensive and time-consuming, due to the numerous possible material choices and combinations, and the required processing conditions. Short development timeframes often limit material choices to previously explored options and prohibit a more comprehensive investigation of possible interface materials. Properties of doped interfaces and/or interfaces with an engineered composition typically are unexplored. Understanding of the
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