$RuO_2$ thin films have drawn much attention due to their good conductivity, low temperature coefficient of resistance (TCR), and high thermal stability Therefore they have been investigated for many applications such as diffusion barrier for oxygen, and electrode material for ferroelectric oxide. Especially, $RuO_2$ thin film has been intensively investigated as a potential electrode material due to the formation of a stable interface with dielectric oxide. It shows better polarization fatigue properties than Pt for ferroelectric random access memory (FRAM) application. It also shows good etching properties to form small features. There are recently considerable interests in the deposition of metallic Ru films for dynamic random access memory (DRAM) application, because $RuO_2$ films are easily prepared with metallic Ru films and the layer of titaniumoxide, which can be formed at interface between $RuO_2$ and TiN during dielectric oxide deposition, descends the electrical properties. The leakage current was greatly increased even though $TiO_2$ layer was formed at just one side either top electrode or bottom electrode. One of the versatile techniques for preparation of the electrode films metallorganic chemical vapor deposition (MOCVD), which offers the advantages of good step coverage and high deposition rates, as well as control over the film composition and thickness.
In this study, thermal decomposition behavior of $Ru(EtCp)_2$ has been studied using thermogravimetry , mass spectroscopy, and in situ infrared spectroscopy under Ar, $H_2$ and $O_2$ atmosphere. Also chemical vapor deposition mechanism of Ru films and properties of the films deposited using $Ru(EtCp)_2$ and new precursor, have been investigated. We compared the properties of the films with the decomposition behavior of precursor. In particular, dissociation of the chemical bonds in the Ru complex ligand has been investigated by monitoring the intensity change of the IR peaks while the sample at vapor state is heated. The Ru complex has stable evaporation property without decomposition at below 150℃, regardless of ambient. The decomposition behavior of $Ru(EtCp)_2$ is sensitive to the ambient gases and the Ru complex is hardly degraded after storage for four months. The chemical bonds in the complex begin to be dissociated at about 300℃ and are decomposed at the almost same time under Ar and $H_{2}$ as the temperature increase. However, under $O_2$, the chemical bonds begin to be dissociated at the lower temperature and are sequentially decomposed at elevated temperature. The Ru-EtCp bonds dissociate most easily, then the ethyl adduct and C-H in Cp at the same time, and finally the C-C bond in Cp bonds under $O_2$, while the C-H bonds in ethyl adduct bond disappear first under Ar. Oxygen gas enhanced the decomposition of Ru complex at low temperature since the bonds strength of Ru complex, especially Ru-EtCp bonds, are decreased by chemisorption of oxygen to Ru. The existence of little oxygen during storage cause the chemisorption of oxygen, so that the Ru-EtCp bonds are more easily dissociated after evaporation, when the $Ru(EtCp)_2$ are stored. Thermodynamically, we confirmed that what oxygen absorb to Ru in $Ru(EtCp)_2$ is stabler that what $Ru(EtCp)_2$ and oxygen gas exist separately using the simulation of D-Mol and Dv-Xα. The decrease of bond overlap population between Ru and EtCp ligand was calculated as the increase of amounts of oxygen to absorb to Ru complex. Because $Ru(EtCp)_2$ +Ox compounds have little ionic bond character, the decrease of bond overlap population means that directly the reduction of bond strength of Ru and EtCp ligand. At the other side, because the hydrogen as well as Ar gas can’t bond with Ru in Ru complex, the decomposition characteristic was not affected by hydrogen gas. Also the adsorption of oxygen affects the various properties of Ru thin films deposited using $Ru(EtCp)_2$, specially step coverage as well as the depositon temperature. The temperature for possible film deposition to have Ru phase decrease from over 700℃ to 200℃ as the oxygen gas was supplied. Because the oxygen gas share the adsorption site with $Ru(EtCp)_2$ precursor vapor as well as the oxygen assist the decomposition of Ru precursor, the oversupplied oxygen gas interfered the adsortion of the precursor so that the step coverage of films were improved.
Metallic Ru thin films by metallorganic chemical vapor deposition with a new precursor named (η 6-Benzene) (η 4-1,3-Cyclohexadiene) Ruthenium were prepared with various solvent reaction gas and ratio of precursor/reaction gas below the substrate temperature of 450℃ and the absolute composition and electrical properties were investigated. The absolute composition including hydrogen was performed by means of elastic recoil detection time of flight (ERD-TOF). The carbon contents in films dramatically decreased as tetrahydrofuran (THF) and oxygen gas were supplied with the precursor during deposition and Ru films deposited using solvent included no oxygen atom and hydrogen gas had higher carbon concentration. Also, oxygen atom improved deposition rate and electrical property but decreased step coverage property due to increasing formationand desorption rate of by-product. Especially, Ru films contained hydrogen component, which was originated hydrogen atoms in precursor. It was shown that grain size among several factors dominantly affected electrical properties of ruthenium films, when Ru films had almost same composition. We could reduce the carbon concentration in Ru film without using any oxygen gas or solvent contained oxygen atom.
