CHEMICAL-VAPOR-DEPOSITION TIN PROCESS FOR CONTACT VIA BARRIER APPLICATIONS

Chemical vapor deposition (CVD) TiN is an attractive replacement for PVD TiN as a barrier and glue layer for subhalf-micron contacts and vias. CVD TiN films have been deposited in a commercial reactor via the thermal decomposition of tetrakis-dimethyl-amino-titanium (TDMAT) precursor in an Nz ambient. The deposition can be characterized by a simple Arrhenius rate expression with a half-order dependence on TDMAT concentration and an activation energy of 0.53 eV. Designed experiments show that the deposition transitions from being kinetically limited at high TDMAT flow rates and low temperatures to transport limited at the other extreme. In the kinetically limited regime; the deposition rate increases with increasing TDMAT mole fraction and increasing temperature. Step coverage simulations have been performed by coupling SPEEDIE (a profile evolution program) with the Arrhenius rate expression. Experimental and simulated step coverages show good agreement over a wide range of process conditions. Step coverage improves with increasing deposition rate and decreasing temperature. Adequate deposition rates (>400 Angstrom/min) with good deposition uniformity and high step coverage (50%-85%) can be achieved. Film stress and roughness are mostly invariant with process conditions. These films are close to stoichiometric (i.e., 1:1 Ti:N ratio), but contain up to 30% carbon. Exposure of these films to air causes rapid oxidation with a steady state concentration of 15%-20% oxygen after 24 h of air exposure. The high carbon concentration results in high film resistivity (5000 mu Omega cm), which doubles after 24 h of air exposure due to oxidation of the film. Film resistivity decreases and him stability improves with increasing N-2 how rate. Electrical characterization of two process variants have been performed. The first provides a film with 85% step coverage with a resistivity of 5600 mu Omega cm, while the second process achieves a lower resistivity of 3700 mu Omega cm and a lower step coverage of 50%. Electrical performance of both films is similar. Contact induced diode leakage is lower for CVD TiN compared to PVD TiN. Contact resistance for 100-200 Angstrom CVD TiN is comparable or lower than 500 Angstrom PVD TiN. A 100 Angstrom CVD TiN barrier is adequate; 300 Angstrom CVD TiN is too thick because of high film resistivity. An Al-Cu/100-300 Angstrom CVD TiN/Si stack shows lower resistance increase after 450-500 degrees C; 30 min N-2 anneal compared to a Al-Cu/200 Angstrom PVD TiN/Si stack indicating that CVD TiN is a superior barrier and is more inert than PVD TiN. (C) 1995 American Vacuum Society.