Cu metallization for sub-0.25 μm interconnects marks not only a change in metallurgy from Al and a change in architecture from subtractive to damascene but also a major shift in deposition technology from sputtering to electroplating. A remarkable feature of electroplated Cu films is the recrystallization or grain growth process that takes place at room temperature over a period of hours to weeks after plating. While this phenomenon has been described for blanket films, the influence of substrate topography on the kinetics of recrystallization has not previously been reported. Using focused ion beam imaging we demonstrate that recrystallization of the small grained as-plated Cu is initiated at the upper corners of damascene trenches and grains continue to grow laterally, eventually transforming the entire film. Removal of overlying Cu by chemical mechanical polishing before the transformation leads to incomplete recrystallization of the Cu left in the trenches. The kinetics of the recrystallization process for trench widths of 0.3, 0.5, 0.8, 2, and 5 μm reveal a minimum time for recrystallization for the 0.8 μm trenches. An acceleration of the room temperature recrystallization rates for all trench widths is observed if the films are first cycled to −78 °C immediately after plating, and a more pronounced minimum time for recrystallization is observed for the 0.8 μm trenches. These observations lead us to propose that the initiation of this process at the upper corners of the trenches and the trench width dependence of the recrystallization rate are related to higher stress or dislocation densities.

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The preparation of Ru and RuO2 thin films by organometallic chemical vapor deposition and an investigation of the films' properties are reported. Ru is of interest for metallization in integrated circuit fabrication because its thermodynamically stable oxide, RuO2 , also exhibits metallic conductivity. As a result, oxidation during processing of Ru is a less critical concern than in current metallization technology. Taking advantage of the benefits of chemical vapor deposition, such as conformal coverage and low temperature, damage‐free deposition, we have deposited Ru, RuO2 , and normalRu/RuO2 by pyrolysis of three organoruthenium complexes. Films of a given phase composition were deposited under a wide variety of conditions and exhibited large variations in electrical resistivity and carbon content. The best Ru film, produced from Ru3false(CO)12 at 300°C in vacuum, had a resistivity of 16.9 μΩ‐cm and exhibited excellent adhesion to Si and SiO2 substrates. The best RuO2 film, produced from normalRufalse(C5H5)2 at 575°C in O2 , had a resistivity of 89.9 μΩ‐cm and similarly exhibited excellent adhesion. Rutherford backscattering studies show that Ru and RuO2 films are effective diffusion barriers between Al and Si up to annealing temperatures of about 550° and 600°C false(1/2 normalh exposurefalse) , respectively. Thus, they are significantly better than the currently used W films, which are only effective to about 500°C.

Scaling analysis and finite element modeling of the governing transport equations are used to show that in the submicron features of damascene ultralarge scale integrated interconnect structures, diffusion of cupric ion and trace additives is the only transport process that affects plating uniformity. Potential variations in solution or in the metal film, while important on wafer (dm) length scales, are completely negligible on feature (m) length scales. Convection is also unimportant in submicron features. As a result, changes in process parameters such as fluid flow rate, barrier film conductivity or thickness, or solution conductivity are unlikely to result in significant changes in plating uniformity or void formation inside trenches and vias. On the other hand, changes in plating current density, feature geometry, or additive concentration in the plating bath will have a large impact on filling profiles. The impact of diffusive limitations on feature filling is described by a dimensionless parameter D . Low values of D indicate that for typical damascene structures and plating conditions, cupric ion depletion is only on the order of a few percent, indicating that copper plating is essentially conformal. Only very deep or high-aspect features will pinch off as a result of cupric ion depletion. For additives that are depleted at the metal surface, values of D can be large, indicating the potential for substantial additive depletion inside trenches and vias. D scales with L 2 /w. As a result, deeper features (larger L) plate less uniformly, as do more narrow features (smaller w). However, if aspect ratios (L /w) are held constant as critical dimensions decrease, beneficial effects of additive depletion will diminish in future device generations.