Control of Metallurgical, Magnetic and Electrical Properties of Electrodeposited CoFeNi Thin Films and Cu Nanostructures



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The ever increasing quality and reliability demand of microsystems indicate that the electrodeposited magnetic alloys used for their fabrication should have minimum possible magnetic losses at the desired frequency range. In order to meet this challenge, the magnetic industry is facing the task of electrodepositing soft high magnetic moment alloys (SHMM) with high permeability (μr>400) and high resistivity (ρ>100μΩ-cm). The ternary ferromagnetic CoFeNi alloys represent the class of SHMM alloys which inherently have a higher resistivity than their binary (NiFe or CoFe) counterparts, with similar magnetic properties. In the first part of this research, the work exploring the development of solution chemistry for the electrodeposition of CoFeNi magnetic thin films is discussed. The experimental results (FIB, EDS, XRD, 4-point probe and VSM) indicate that a high deposition rate CoFeNi film can be deposited from the developed bath chemistry yielding high saturation magnetization (Ms~2.0 T), high relative permeability (μr~700) and high resistivity (ρ~100μΩ-cm). Additionally, the effect of sulfur containing additives like saccharin on the physical, electrical and metallurgical properties of CoFeNi films is studied. The role played by saccharin in stress reduction is exhibited by performing in-situ stress measurements during thin film growth. The second part of this dissertation focuses on a novel approach towards improving the conductivity of Cu interconnects at nanoscale. The externally applied strain on the Cu interconnects during annealing is used to promote the grain growth via grain boundary densification process. The results indicate that this approach yields positive effect on the resistance of Cu interconnects. The drop in the resistance after annealing at 200°C and 250°C is observed for externally imposed compressive strain along the Cu interconnects with critical dimensions (CD) of 50nm and 64nm. The analysis and results suggest that the compressive strain during annealing induces densification of the grain boundaries with the interface vector parallel to the current path. These results are of great significance for the overall improvement of conductivity of the Cu interconnects as well as reliability and life span of microelectronic devices.



Soft magnetic alloys, Saturation Magnetization, Coercivity, Resistivity, Cu interconnects, Nanoscale, Strained annealing, Critical dimension, In-situ stress/strain measurements