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Ultra-thin titanium and tantalum nitride layers grown on three different dielectrics were studied to examine how low-energy ions change the chemical composition at and near their interface. Comparisons were made by growing titanium and tantalum nitride under similar conditions both with (ion-assisted) and without (reactive) nitrogen ions. Although the chemical reactions between the nitrides and the three dielectrics under both growth conditions depend on the type of dielectric used, a few general observations were seen. In comparison with the reactively grown samples, all of the ion-assisted growths show a significant increase in the amount of nitride in the nitride layer at and near the nitride/dielectric interface. Moreover, the amount of chemical binding between the titanium nitride and dielectric is increased when low-energy ions are used. Angle resolved x-ray photoemission determined that the enhancement in the deposition process from low-energy ions occurs without inducing significant intermixing between the nitride layer and dielectric. Although thicker layers of titanium nitride show a difference in the grain structure from ion deposition1, the ultra-thin layers grown in this work do not have any dependence with ion-assisted growth for the samples measured.
TiN and TaN thin films are proposed as barrier layers between copper interconnects and low dielectric constant (low-k) polymers. As the barrier layer thickness is scaled down, the uniformity and morphology of these films will be severely affected by the nitride-polymer interface and become an important issue for the reliability of the whole interconnect structure. In order to evaluate nitride formation and the interfacial chemistry we deposited TiN and TaN on fully cured low-k polymers by two different techniques: reactive evaporation of the metal in nitrogen ambient and by ion assisted reactive deposition using a low energy (100 eV) nitrogen ion beam during evaporation. Photoelectron spectra were recorded in situ for metal coverages from 0.1 nm until bulk like metal or metal nitride spectra were obtained. Nitride concentrations, extracted from the photoelectron spectra, show that even though very similar nitride films are produced by both techniques for thicker films (>5 nm) we only find significant amounts of nitride at the interface in the ion assisted case. Thinner films formed in nitrogen ambient were very similar to those where the pure metal was deposited and were dominated by the formation of compounds with carbon and oxygen from the polymer. This shows that the composition of barrier layers can be drastically altered near the polymer interface. Low energy ions in contrast allow the growth of more homogeneous films which can significantly improve the reliability of copper based high density interconnects.
The adhesion of Al(Cu-Si) line structures on thin films of BPDA-PDA with different surface preconditioning were examined by measuring the deformation energy of the metal and interface. The properties of BPDA-PDA/Al(Cu-Si) were examined with atomic force microscopy (AFM). Although different sputtering treatments profoundly affect the adhesive properties, the sputtering does not appreciably change the topology of the BPDA-PDA. We also found evidence that even though the thickness of the interface can be very small (3–5 nm), the polymer/metal interface can greatly affect the deformation behavior of the entire system.
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