Diffusion characteristics of copper in novel metallic films

The goal of this work was to synthesize refractory materials like TiN, Ta and alloys of TiN-TaN in the form of thin films which are used as diffusion barriers in integrated circuits to prevent diffusion of Cu into the Si substrate. The primary emphasis of this research was to synthesize different microstructures of these films like amorphous, nanocrystalline, textured polycrystalline and single crystalline films, and to study the effect of these microstructures on their mechanical and electrical properties and on diffusion characteristics of Cu.; Microstructures ranging from nanocrystalline to single crystalline TiN films on Si(100) substrates were synthesized by Pulsed Laser Deposition technique by varying the substrate temperature from 25°C to 650°C. Experimental techniques like XRD, TEM, HRTEM, STEM-Z, EELS, SIMS and four-point probe resistivity measurement were used for in-depth analysis. Effect of microstructures of these films on their mechanical and electrical properties, and on diffusion behavior of Cu was analyzed. An important finding of this research was that polycrystalline TiN films showed significantly more diffusion of Cu along the columnar grain boundaries, whereas nanocrystalline films exhibited significantly less diffusion of Cu comparable to that in single crystalline TiN films.; Impurity induced amorphous Ta films stable up to high temperatures (∼650°C) were synthesized by the Pulsed Laser Deposition and polycrystalline Ta films were processed by magnetron sputtering technique. Effects of different microstructures of these films on their electrical properties and on the diffusion characteristics of Cu were analyzed. Using the above experimental techniques along with RBS, stable amorphous Ta films showed insignificant diffusion of Cu. Polycrystalline Ta films showed significant diffusion of Cu along the grain boundaries. Recrystallization of amorphous Ta films and diffusion along the grain boundaries were observed at higher temperatures.; The effect of alloying TiN and TaN to combine their useful properties as a diffusion barrier for Cu was analyzed. Different TaxTi 1-xN alloys with x ranging from 0.3 to 0.7 were obtained by arranging the target in a special configuration and ablating it in a sequential manner by Pulsed Laser Deposition. Superlattice structures of TaN and TiN were achieved for x = 0.6. By using single crystalline cubic TiN as a buffer layer, cubic phases of all the alloys were obtained with low resistivity values. Nanoindentation measurements provided high hardness values of the alloys making them useful for hard coating applications. Insignificant diffusion of Cu was observed for all the concentrations after high temperature annealing and these studies proved TiN-TaN binary components to be a superior diffusion barrier for Cu.