| Summary: | 博士 === 國立交通大學 === 材料科學與工程系所 === 94 === In semiconductor manufacturing, as device dimensions continue shrinking into deep sub-micro regime, high packing density Cu multilevel interconnection technology has been developed due to its lower resistance and parasitic capacitance for increasing ULSI operating speed, compared to the conventional aluminum-alloy metallization. As considering the integration of Cu metallization, the damascene process has been expected to be very promising for fine Cu feature in IC backend metallization process. Therefore, in this thesis, the major investigations in the damascene process are carried out by improving the performance of the Cu electroplating deposition, the multi-steps metal CMP planarization and the following post CMP cleaning.
To enhance the capability of gap-filling into high-aspect-ratio vias and trenches, it should to be optimized with additives by monitoring the filling ration Δy/Δx between ‘‘bottom-up’’ with ‘‘sidewall shift’’ from the cross section of a partially filled copper profile and achieved the superfilling performance for 0.15μm vias with aspect ratio 6 by an acid-copper electrolyte with polyethylene glycol, Cl﹣, and 2-mercaptopyridine (2-MP). The superfilling dynamics was explored with the adsorption-diffusion model, which explains the behavior of additives providing selective inhibition gradient within the damascene feature. On the other hand, we also propose an effective seeding technology, plasma immersion ion implantation of palladium (PIII Pd), to achieve defect-free gap-filling for copper electroplating (Cu-ECP). It was found that a threshold dosage of PIII Pd seed is required to drive Cu-ECP. To enhance the gap-filling capability, a higher substrate bias of PIII Pd is suggested to achieve the bottom-up phenomena of Cu-ECP and obtain the Cu (111) formation of electroplated copper films.
To develop the global planarization technology for damascene process, a novel in-situ electrochemical measuring system was established for exploring Al CMP dynamical corrosion and to elucidate the polishing mechanisms. Firstly, Al CMP is carried out to investigate the influences of H2O2 concentration, slurry pH, and surface oxide formation-abrasion mechanism on Al and Ti in the H3PO4-H2O2-based chemistry. From these electrochemical results, the removal rate of polishing aluminum is limited to its passivating oxide removal by mechanical abrasion or chemical dissolution and titanium is limited to the formation rate of surface oxide. Correspondingly, the removal selectivity issue of Al CMP can be effectively controlled by means of slurry formulation.
In order to better understanding the tribo-chemical schemes of Cu CMP, the characteristics of abrasive studies focus on the results from the interaction of abrasive wearing and chemical corrosion of copper thin film in formulated slurries with sub-micron sized alumina abrasives of varying phases controlled mainly by calcinations condition. Polishing with high Cu dissolution rate formulation, Cu removal rates varied linearly with the particle size, suggesting an indentation-limited model. On the contrary, polishing in certain dissolution-limited circumstances such as DI water or H2O2 alone, the characteristics of alumina abrasives, do not manifest onto the low Cu removal rate, but exhibit a threshold removal behavior at low-temperature transition phase Al2O3 followed by a dramatically saturation removal rate at nearly mono α-Al2O3. By use of the corrosion-inhibited slurry, note that a contact surface-limited mechanism was first introduced for the inverse Cu polishing behavior with mixed-phase Al2O3. Higher Cu removal rates and lower roughness were due to the both effects of the higher reactive performance by the smaller abrasives and the higher mechanical abrasion power by the larger abrasives.
From our preliminary investigations, multi-step Cu damascene CMP with different copper removal rates and polishing pads is used to eliminate topography efficiently. In colloidal-silica-based slurry, the polishing behaviors of copper, tantalum and silicon dioxide are found to relate to the kind of alkaline additives. The size of cations from alkaline additives influences the zeta potential of slurries, so as to vary the material removal rate. During the 2nd step of Cu damascene CMP, the addition of small-sized K+ from KOH provides high removal selectivity of tantalum/copper and oxide/copper, so as to benefit the reduction of copper dishing.
Finally, a superior post Cu CMP cleaning chemistry in neutral pH is formulated by adding ionic carboxylic acids into ammonium-based solution with inhibitors, and developed to effectively remove not only alumina but colloidal silica particles left on the polished wafer, meanwhile not to cause copper wires corrosion. In another research, we also find that the use of D-sorbitol and PVA aqueous cleaning solution with sponge PVA brush scrubbing have good performance on colloidal silica particle removal ability on post Cu CMP cleaning.
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