Atomic layer deposition and properties of refractory transition metal-based copper-diffusion barriers for ULSI interconnect
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Refractory transition metals have played an important role in the manufacturing of microelectronic devices for interconnect applications including metal contacts, adhesion layers, and diffusion barriers. The diffusion barrier application has become crucial for the integration of copper as the choice conductor in ultra-large scale integrated (ULSI) circuit interconnect. The refractory metal tantalum has been used commercially in previous ULSI technology generations, and atomic layer chemical vapor deposition (ALD) processes for this metal are highly desired for its use in future generations. This dissertation presents surface chemistry and film growth investigations exploring tantalum ALD and an investigation of barrier film adhesion to relevant interconnect surfaces. 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 TaCl5, which was used in the first reported Ta ALD process, on a polycrystalline Ta surface. Based upon these results and those of recently published works, a TaF5/Si2H6 precursor chemistry for Ta ALD was proposed. In this method, alternating half-reactions, which, in this case, are the reaction of TaF5 with a Si2H6-treated surface (the TaF5 halfreaction) and the reaction of Si2H6 with a TaF5-treated surface (the Si2H6 halfreaction), are used sequentially and repetitively to deposit a film. The adsorption and half-reactions of these precursors in the range of 303 to 523 K on polycrystalline Ta were studied in ultra-high vacuum using XPS, TPD and secondary ion mass spectrometry. These half-reactions were subsequently used in practice to deposit thin Ta films in a specially designed, research-scale ALD reactor. This is the first non-plasma enhanced method reported to deposit Ta by ALD. Finally, the adhesion properties of similar tungsten carbide thin films to SiO2 and candidate low-permittivity dielectric substrates was characterized by the four-point bend delamination technique.