Reactive deposition of pure and alloyed cobalt and nickel thin films from supercritical carbon dioxide solutions
The need for faster and smaller integrated circuits and other devices is necessitating deposition of interconnect materials in increasingly narrow high aspect ratio features, a demand that can not be fully realized by current techniques. Traditional metal deposition techniques such as plating and CVD have limitations for yielding uniform and conformal coverage. Although plating techniques offer high reactant concentrations, high surface tension and sluggish liquid-phase mass transport preclude uniform deposition in complex geometries. Moreover, the plating techniques generate large quantities of hazardous wastes. CVD offers very good gas phase transport properties including low viscosity, rapid diffusion and absence of surface tension. However, CVD is constrained by precursor volatility that often leads to low vapor phase concentrations and mass transfer limited reactions that preclude uniform deposition in high aspect ratio trenches. Chemical fluid deposition (CFD) is a relatively new approach that involves the chemical reduction of organometallic precursors dissolved in supercritical carbon dioxide by H2 or alcohols. CFD is essentially a hybrid technique that combines the advantages offered by both the plating techniques and CVD while minimizing their disadvantages. Like the plating techniques, CFD is solution-based, offering orders of magnitude higher precursor concentration compared to CVD. Since the transport properties of supercritical fluids are more like those of a gas, CFD retains the advantages associated with CVD yielding conformal coverage and uniform filling of sub-100 nm features.
In this dissertation, the versatility of CFD for the deposition of pure and alloyed cobalt and nickel films was demonstrated using a batch, cold-wall CFD reactor. High purity films of pure and phosphorous-doped cobalt and nickel were deposited on several types of substrates in a single step without the need for catalytic seed layer. Binary cobalt-copper and cobalt-nickel films were deposited over a wide range of composition. The deposition of nickel-palladium films was also attempted. The deposited films have potential applications in microelectronics and magnetic devices. Pure and doped cobalt films are of interest in microelectronics to improve the performance of copper as an interconnect material. Cobalt containing thin films such as cobalt-copper and cobalt-nickel are used for data storage and other magnetic devices.