Ionized physical vapor deposition of titanium nitride: A global plasma model

A global plasma model for an ionized physical vapor deposition (IPVD) system is described. The model predicts the density of electrons, excited state, Ar and N2, ironized Ar, N2, and Ti, the density of atomic N and N+, and the electron temperature. The computed results are compared to experimental measurements of a titanium nitride IPVD reactor to confirm the validity of the model. The reactor consists of an inductively coupled plasma source that is fed by argon, nitrogen, and sputtered titanium. The dissociation of nitrogen in the discharge is typically found to be in the range of 10%–30%. The electron temperature is 1.8 eV, and the ion density is between 2×1011 and 6×1011 cm−3. The ion density is found to decrease as nitrogen is added to the Ar discharge due to collisional losses associated with molecular states. In the metal mode of operation, the atomic nitrogen density is suppressed by the Ti-rich reactor walls. As the nitrogen flow rate is increased, the target and walls become nitrided and the density of N increases an order of magnitude to 2–4×1012 cm−3. The ionization fraction for the depositing flux of titanium is typically 0.4–0.7. The model is easily adapted to other technologically relevant diffusion barrier layer materials such as WN and TaN.