Controlling nucleation and growth of ultra-thin ruthenium films in chemical vapor deposition
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As feature sizes in microelectronic devices decrease, ultra-thin (< 3 nm) and smooth diffusion barriers are required to prevent copper from diffusing into the surrounding dielectric layers and to limit electron scattering at the copper-liner surface. Chemical vapor deposition (CVD) is one route to these barriers. The inhibitor gas adsorbs on metal nanoparticles, forces additional nucleation and enhances nucleation density. Island growth combined with a sparse nucleation density leads to film roughness and the deposition of more metal mass than is needed to form a film of sufficient thickness to function as a copper diffusion barrier when compared to a uniformly-thick metal film. In the first study, a higher nucleation density and smoother Ru film is achieved in CVD with CO addition during growth. CO competes with Ru3(CO)12 for free hydroxyl adsorption. The CO addition to Ru3(CO)12 deposition at proper timing and effective partial pressure reduces the film growth rate, surface roughness and nanocrystalline grain size by chemical vapor deposition. The second study reports the use of ammonia to inhibit the growth of previously-nucleated ruthenium islands and force the nucleation of additional islands such that thinner films form as the islands coalesce with continued growth using Ru3(CO)12. The ammonia addition reduces the film nanocrystallinity and the films appear X-ray amorphous with the highest ammonia partial pressure during film deposition. In the third study, films grown from Ru(tBu-Me-amd)2(CO)2 form a 2D wetting layer before 3D particle growth is observed. CO and ammonia addition to the gas phase during film growth from Ru(tBu-Me-amd)2(CO)2 leads to smoother films by inducing surface reconstructions during the film growth; these gases also lead to films with lower resistivity and lower crystalline character. Overall, this research is to understand how blocking adsorbed moieties effect the nucleation of metals on a silica substrate, and to discover the principles leading to ultra-thin and smooth metallic films in CVD.