Growth and characterization of Ru films deposited by chemical vapor deposition : towards enhanced nucleation and film properties
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As device dimensions in integrated circuits scale down, there is an increasing need to deposit ultra-thin, smooth, continuous films for use in applications such as the liner in back end processing. The liner must have good adhesion to both Cu and the dielectric, act as a Cu diffusion barrier, and be conductive enough to allow the electroplating of Cu. Ruthenium (Ru) has been considered as a possible material to be implemented into the liner due to its low electrical resistivity, high thermal and chemical stability, and negligible solubility with copper. Chemical vapor deposition (CVD) is an attractive growth technique for Ru films because it allows conformal deposition in high-aspect ratio features. However, there are some limitations that must be overcome in the deposition of Ru films. CVD Ru films suffer from poor nucleation on oxide and nitride substrates. Poor nucleation leads to rough, large-grained polycrystalline columnar films, which may not coalesce into a continuous film until the thickness greatly exceeds the requirements for the liner. This dissertation presents surface chemistry and film growth studies involving Ru CVD and focuses on improving the nucleation and properties of Ru films. In situ surface analysis techniques including X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) were used to study the fundamental adsorption behavior of the Ru precursor, (2,4- dimethylpentadienyl)(ethylcyclopentadienyl)Ru or DER, on polycrystalline Ta, both with and without iodine adsorbed on the Ta. Based upon these results, CVD films were grown using DER/O₂, and it was shown that nucleation and film properties can be improved by the addition of methyl iodide. Ru films grown using DER/O₂ show sparse nucleation, which leads to very rough surface topography and large polycrystalline columnar grains. The addition of methyl iodide during growth significantly improves nucleation and results in smoother, smaller-grained films. Iodine adsorbs on the initially-formed Ru islands and continuously segregates through the film to the surface during the entire deposition. In addition, CVD films grown with Ru₃(CO)₁₂ were studied. Use of the Ru₃(CO)₁₂ precursor results in thin, ultra-smooth films that show little to no columnar grain structure.