Improvement of TiN flow modulation chemical vapor deposition from TiCl ₄ and NH₃ by introducing Ar purge time

TiN films were deposited by using TiCl₄/NH₃ flow modulation chemical vapor deposition (FMCVD). FMCVD consists of repetitive TiN deposition periods by TiCl₄/NH₃, each of which is followed by Cl reduction period. TiN deposition periods are typically 3 s and Cl reduction periods are Is. The effect of the number of deposition/reduction cycles and the effect of the partial pressure of TiCl₄ and NH ₃ on film uniformity and resistivity were investigated. For a total reduction period of 100 s, increasing the number of reduction periods from 100 × 1-s periods to 300 × 0.33-s periods decreased the step coverage. This decrease in coverage was due to residual TiCl₄ during the Cl reduction period by NH₃ that cleared out TiCl₄ at a constant rate, independent of the length of the period of reduction cycle. An Ar purge cycle was used between the deposition and reduction cycles to allow the residual TiCl₄ to clear out before the NH₃ was used for the film reduction cycle. This significantly improved the film step coverage from 50% to over 90%. The minimum film resistivity occurred when the NH ₃ partial pressure was 0.25 Torr. NH₃ partial pressure less than 0.25 Torr inhibited film reduction, and NH₃ partial pressure higher than 0.25 Torrenhanced the deposition rate, which also inhibited film reduction. By using the optimum conditions determined in this study. we could obtain TiN films that had film resistivity of about 240μΩ·-cm and step coverage of about 98% at 410°C.