The Effect of Low-Energy Nitrogen Ions on the Growth Modes of Nitrides on Polymers used in the Microelectronics Industry
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P. ABRAMOWITZ*, M. KIENE**, P. HO** * Physics Department, University of Texas at Austin, Tx 78713, [email protected] ** Microelectronics Research Center, University of Texas at Austin, Tx 78713 ABSTRACT
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 lowenergy 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 deposition', the ultra-thin layers grown in this work do not have any dependence with ion-assisted growth for the samples measured. INTRODUCTION
The main driving force behind research and development in the microelectronics industry in the last few decades stems from the need to decrease feature size and to use new materials in
interconnect structures. Copper is the future metal to be used in interconnect structures and will function as the current carrying wires between the transistors. The problem with copper is that it can easily diffuse into the dielectric that surrounds the copper. A diffusion barrier is placed between the two layers to prevent diffusion and to increase the adhesion between them. Since the diffusion barrier, usually a refractory metal or its nitride equivalent, is not as conductive as copper it is beneficial to keep the thickness as low as possible. Practically only a few nanometers worth of diffusion barrier is needed to act as a robust diffusion barrier which implies a nitride layer of the same thickness. Low-energy bombardment or deposition methods which use lowenergy ions or neutrals are quite common 2, but the growth of diffusion barriers in microelectronics is more sensitive to the interfacial properties than the bulk properties. The initial substrate plays a large role in determining the type of film that grows on it, and future dielectrics in the microelectronics industry are mostly polymers which presents their own unique challenges since they are susceptible to damage from ion bombardment. In order to examine the interfacial growth of nitrides on polymers, low-energy ions were used to examine how they effect the interface between titanium and tan
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