CMP of metal and dielectric films for microelectronic applications

Advances in the semiconductor industry are occurring at a rapid pace with an increasing use of better materials and newer techniques. One such example is the replacement of aluminum by copper as an interconnect material. Damascene and dual-damascene processing, combined with chemical-mechanical planarization (CMP), has enabled effective incorporation of copper into integrated circuit (IC) manufacturing. Similarly, shallow trench isolation (STI) has offered superior dimensional control over conventional local oxidation of silicon (LOCOS) and helped in increasing the device density. However, coupled with these new techniques are different sets of challenges, which need to be resolved before completely accommodating them in mainstream production. This thesis work is directed towards alleviating some of the problems associated with Cu damascene and STI CMP processing.; Results of copper and tantalum disk polishing with the slurries containing alumina and silica abrasives with and without oxidizing agents such as peroxide and peroxide/glycine have been reported in this thesis. The effects of these oxidizers are scanned over a pH range of 2 to 12 and possible mechanisms of material removal during CMP are proposed based on indentation and electrochemical measurements. Profound effect of slurry pH on the polish rates of Cu and Ta indicates that the polishing selectivity of these two materials can be easily controlled by the change in slurry pH.; A slurry formulation for CMP is also proposed wherein the slurry is a suspension of more than one type of abrasives in a chemical solution. These mixed abrasive slurries (MAS) containing a combination of alumina/silica and alumina/ceria particles are evaluated for CMP of metal and dielectric films, respectively. With proper composition of mixed abrasives containing alumina and silica particles, it is possible to formulate slurries which are highly selective to Ta polishing during Cu damascene CMP. Similarly, a mixture of alumina and ceria particles gives silicon dioxide to silicon nitride polish rate selectivity as high as 65 without any additives. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) of the slurry particles have indicated formation of a sheath by the small particles around big particles. It is proposed that the adsorption of nano-size particles (silica and ceria) on large (alumina) particles is the reason for enhanced CMP performance by MAS.; Also, as a part of this thesis work, two commercially available pads, namely, Suba-500 and IC-1400 with k-groove are evaluated in terms of their slurry transport characteristics. It is observed that the IC-1400, which has a porous and grooved surface structure, is more efficient in carrying the slurry abrasives and chemicals to the film/pad interface during polishing.