Low sheet resistance titanium nitride films by low-temperature plasma-enhanced atomic layer deposition using design of experiments methodology

A design of experiments methodology was used to optimize the sheet resistance of titanium nitride (TiN) films produced by plasma-enhanced atomic layer deposition (PE-ALD) using a tetrakis(dimethylamino)titanium precursor in a N₂/H₂ plasma at low temperature (250°C). At fixed chamber pressure (300 mTorr) and plasma power (300W), the plasma duration and N₂ flow rate were the most significant factors. The lowest sheet resistance values (163Ω/sq. for a 20nm TiN film) were obtained using plasma durations ∼40s, N₂ flow rates >60 standard cubic centimeters per minute, and purge times ∼60s. Time of flight secondary ion mass spectroscopy data revealed reduced levels of carbon contaminants in the TiN films with lowest sheet resistance (163Ω/sq.), compared to films with higher sheet resistance (400-600Ω/sq.) while transmission electron microscopy data showed a higher density of nanocrystallites in the low-resistance films. Further significant reductions in sheet resistance, from 163Ω/sq. to 70Ω/sq. for a 20nm TiN film (corresponding resistivity ∼145 μΩ·cm), were achieved by addition of a postcycle Ar/N₂ plasma step in the PE-ALD process.