The limitations of sputtered TiW as a blanket tungsten nucleation layer

The authors discuss the application of sputtered TiW as a nucleation/barrier layer for blanket CVD tungsten. A serious next generation concern is whether the current TiW process has adequate step coverage to protect the device during CVD tungsten processing. To answer this question, computer models (SAMPLE) of sputtered TiW thickness profiles were validated by comparison to experimental results. The model was then used to predict the TiW step coverage expected in aggressive aspect ratio contacts and was applied to an older generation BiCMOS structure to generate a similar range of TiW thicknesses for electrical characterization. Diode leakage currents and contact chain resistances were used to determine a practical limit to the contact size and aspect ratio