Ruthenium is attractive for a number of reasons: 1) high chemical and thermal stability with high-k materials; 2) no detrimental interface reactions or interdiffusion at the ruthenium-dielectric interface (i.e. most suitable noble metal electrode material); 3) potential capacitor electrode material for DRAMs and FRAMs, and potential gate metal in future metal-oxide-semiconductor field effect transistors (MOSFETs) due to is relatively high work function (4.7eV); 4) barrier and seed layer for copper, the interconnection metal in microelectronics. Since atomic layer deposition (ALD) is a technique of choice for deposition of thin, uniform, and conformal film growth even on structured surfaces such as trenches and via holes, there is an active search for ruthenium ALD precursors possessing appropriate physical and chemical properties, which are important for the development of a proper deposition process. There is also the need to understand the chemical interaction of these new precursors with various surfaces and the mechanism of ALD growth, requiring in-situ characterization.
In this study, we present in-situ Fourier transmission infrared (FTIR) studies of ALD growth of cyclopentadienyl ethylruthenium dicarbonyl [CpRuEt(CO)2] and O2. There is no measurable ALD of RuEt below 200oC. At higher temperatures, the RuEt begin to react with both SiO2/Si(100) and H-terminated Si(111) surfaces. The reaction is complete at 300oC. Since the precursor decomposes at 350oC leading to CVD growth, the ALD window is very narrow. The IR spectra give clear evidence for ligand exchange and adsorption of surface species, making it possible to identify and quantify surface chemical reactions during the ALD process. IR absorption measurements also make it possible to observe the electronic absorption associated with the growth of Ru and RuO2 films, with a transition from isolated, nucleated film to a continuous film. At that point, the absorbance is higher at lower frequencies, indicative of Drude absorption.