Tantalum (Ta) and nitrogen-contained tantalum (Ta-N) thin films are sputter deposited on Si-based substrates with and without a titanium adhesion layer. The impact of varying the nitrogen flow rate and the underlying titanium on the phase formation process is investigated using X-ray diffraction analysis, resistivity measurement and scanning electron microscopy. Our results indicate that the titanium layer inhibits the formation of high-resistivity tetragonal beta -Ta, and leads to the deposition of low-resistivity cubic alpha -Ta arising from its epitaxial orientation on the underlying titanium. Consequently, the electrical properties and microstructures of the Ta-based films are significantly changed.