Reliability of Plasma Etched Interconnect Lines and Applications in Solid State Electronic and Optoelectronic Devices

Abstract

Plasma etching has been widely applied in fabrication processes of integrated circuits. However, the most popular interconnect material, copper, can hardly be dry-etched due to the low volatility of plasma-copper reaction compounds. A two-step plasma-based process was reported, which involves a plasma chlorination/bromination step and a subsequent dilute hydrochloric acid solution dipping step. The above process enabled room temperature plasma etching of copper with a rate of over 200 nm/min. Nevertheless, halogen gases are toxic and corrosive. In this dissertation, a novel method is developed using an oxygen plasma based two-step etching process. Copper is first converted into copper oxide and dissolves in a dilute hydrochloric acid solution. The method utilizes an environmentally-friendly gas and has been successfully demonstrated under room temperature. Reliability is a critical property of interconnect metal lines. Metal lines can easily be oxidized or contaminated. An additional capping/passivation layer can protect metal lines from environmental effects. Plasma-etched copper lines with titanium-tungsten and molybdenum capping layers were tested by electromigration stress. Under high current density, Cu diffusion into metallic capping layers accelerated voids formation. There is a tradeoff between extending lifetime and reducing contamination. To mitigate the issue, a self-aligned copper oxide passivation method is introduced. A thin oxide layer is grown by plasma oxidation, and the passivation structure reduces environmental effects with mere sacrifice on lifetimes. Ruthenium is an alternative barrier and interconnect material with less resistivity scaling when dimensions shrink. Ruthenium lines and copper lines with ruthenium barrier were stressed with constant current densities or voltages, and they possess longer lifetimes than copper control samples. Conventional light emitting devices are widely used for lighting applications. However, they only emit single wavelength lights. A MOS capacitor based solid state incandescent light emitting device was fabricated and studied under various substrates, annealing temperature, dielectric thicknesses, embedding materials, and gate voltages. The selection of substrate and process parameters influences the electrical and optical properties of the device. The device can emit broad band white light, and it has the potential for a wide range of electronic/optoelectronic applications.