Diffusion barrier properties of thin selective chemical vapor deposited tungsten films

Diffusion barrier properties of selective chemical vapor deposited (CVD) tungsten to silicon and aluminum interdiffusion have been investigated using secondary ion mass spectroscopy, x-ray diffraction analysis, and scanning electron microscopy. Samples of titanium layered pure aluminum on selective CVD tungsten on cleaned silicon wafers were prepared and sintered between 450 and 520 °C. The Ti layered aluminum was used to increase the capacity for silicon to facilitate the outdiffusion from the substrate. Magnetron sputter deposited Ti:W samples were also included in the analysis for comparison purposes. The experimental results indicated that 73 nm of selective tungsten with sheet resistance of 1.5 Ω/⧠ was sufficient as a diffusion barrier for both aluminum and silicon at 450 °C for 30 min, but failed at 520 °C for 30 min. 33 nm thick selective tungsten with 7 Ω/⧠ sheet resistance failed to prevent interdiffusion of aluminum and silicon even at 450 °C for 30 min. 100 nm of Ti:W remained an excellent diffusion barrier for anneals up to 485 °C for 30 min, but did not prevent Si outdiffusion at 520 °C, 30 min. No aluminum penetration was seen in Ti:W samples up to 520 °C. A ternary Ti–W silicide was identified at sintering temperatures as low as 485 °C. A possible formation mechanism is herein proposed.