Synthesis and characterization of plasma enhanced chemically vapor deposited tantalum films

A low temperature inorganic plasma-enhanced chemical vapor deposition (PECVD) process has been developed for the growth of Ta using tantalum pentachloride (TaC15) as the preferred precursor and hydrogen as the reactant gas. Ta coatings were deposited at substrate temperature of 370-400 °C, reactor working pressures of 0.7-2 Ton, hydrogen carrier flow rate of 10-20 sccm, hydrogen reactant flow rates of 500 sccm, and plasma power ranging from 60 to 100W. Ta coatings were characterized with respect to their chemical, structural, and morphological properties by Auger electron spectroscopy (AES), x-ray diffraction (XRD), atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and x-ray reflectivity (XRR). The hydrogen concentration was detected by NRA. These studies indicated that a phase predominant Ta coatings with traces of oxygen, carbon, chlorine, and hydrogen were deposited by PECVD method. The coatings properties had been investigated in relation to deposition temperature, precursor temperature, RF input power, plasma working distance and reactant concentration. The growth rate was significantly enhanced by decreasing the plasma working distance between the plasma shower head and substrate. The growth rate increased with increasing in the precursor temperatures and deposition temperatures. The plasma working distance was also discussed as the main experimental parameter to cause a-phase formation in PECVD Ta deposition. The in-situ annealing process was produced to evaluate effects of thermal treatment of Ta phase formation. XRR measurements showed that the density of the CVD Ta coatings is closed to that of bulk Ta. The various seed layers were used to try to promote the a-phase formation, such as Cr, Au, Nb, Pt, Ti, and TaNx. Tantalum coatings had successfully been deposited on all different seed layers. The SEM results exhibited dense Ta coatings with perfectly conformal coverage. The typical topography of CVD Ta coatings were indicated by AFM analysis. The a-phase promoting effect of those seed layers was indicated by XRD analysis. XRD analysis indicates that mixture a and 13 phase were deposited on the Cr seed layers, but Cr seed layers do not promote a phase formation. However, sputtered Cr gave more crystalline R phase formation. CVD Ta coatings deposited on Nb and Au seed layers no longer exhibited evidence of 13 phase. XRD results of CVD Ta coatings deposited on TaNx seed layers showed predominant presence of a phase formation