Paper SS-ThP23
Surface Chemistry of (2,4-dimethylpentadienyl) (ethylcyclopentadienyl)Ru on Polycrystalline Ta

Thursday, October 18, 2007, 5:30 pm, Room 4C

As device dimensions in integrated circuits scale down, there is a need to deposit ultra-thin, conformal, continuous films for various microelectronic applications. Ruthenium (Ru) thin films are promising candidates for applications such as diffusion barriers in copper metallization and capacitors in dynamic random access memories. Chemical vapor deposition and atomic layer deposition have been used to deposit Ru thin films using a variety of precursors, but the surface chemistry of these precursors is largely unexplored. This work examines the surface chemistry of (2,4-dimethylpentadienyl)(ethylcyclopentadienyl)Ru [DER] on a polycrystalline tantalum (Ta) foil, with and without the presence of methyl iodide. X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) were used to study the adsorption and desorption behavior. Because DER was found to dissociate negligibly at room temperature and above, low temperature experiments were used to examine the interaction of the DER with the Ta foil. The DER was dosed onto Ta at 140 K and then desorbed during the TPD process; XPS spectra were taken both before and after TPD. The DER adsorbs and desorbs molecularly, although a small amount of dissociation occurs during TPD. Both XPS and TPD results indicate that the DER saturates on the surface at an exposure of about 4 Langmuir (L); no multilayers are formed. For exposures up to 0.5 L, a single TPD desorption state is observed at 272 K. As coverage increases, the single state splits into two desorption features which are centered at 264 K and 297 K at saturation. The two states are attributed to different physical states of the molecules; possibly two different molecular orientations occur on the surface. The Ru 3d_3/2 XPS feature shifts from 286.2 eV to 287.3 eV as exposure is increased from 0.1 L to saturation, a binding energy (BE) change of about 1 eV; the Ru 3d_5/2 XPS feature also shifts up by 1 eV. The BE shift with increasing coverage is consistent with the presence of two adsorbed states. Because other research has shown alkyl iodides enhance the nucleation of Ru films, methyl iodide was co-dosed into the chamber along with the DER in an attempt to promote dissociation at room temperature and above. The addition of methyl iodide enhanced the dissociation of DER as compared with the molecule alone. This talk will discuss the surface reactions of DER in the presence and absence of adsorbed iodide.