Alternative Surface Reaction Route in the Atomic Layer Deposition of Titanium Nitride Thin Films for Electrode Applications

Titanium nitride (TiN) thin films grown by atomic layer deposition (ALD) have attracted considerable attention as electrode materials in semiconductor device applications, such as logic transistors and dynamic random access memories (DRAMs). TiCl4 and NH3 are mostly used as the Ti precursor and nitrogen source for the TiN ALD process. Unfortunately, the resistivities of TiN films increase with decreasing ALD process temperature. The resistivity of TiN films especially increases substantially (>150 μΩ·cm) at an ALD process temperature lower than 400 °C because of the remaining Cl impurities (>3%) coming from the TiCl4 precursor. Consequently, a process temperature higher than 500 °C is necessary to achieve a low resistivity of the TiN film. In this study, we provide the first demonstration of a renovative ALD method to decrease the resistivity of TiN films via a novel ALD surface reaction pathway. As a result, a lower resistivity (<130 μΩ·cm) was obtained at the given ALD process temperature (∼<400 °C) compared to that of the conventional TiCl4 + NH3 ALD process. H2S was introduced after the TiCl4 pulse to form titanium sulfide, which was transformed to titanium nitride by the following NH3 gas. With the proposed reaction pathway, the resistivity of the TiN film was decreased by >20% at the given growth temperature compared to TiN films with the conventional TiCl4 + NH3 ALD process. Owing to the effect of H2S during the ALD surface reaction, the Cl impurity was reduced substantially (∼1%) in the TiN film, which eventually decreased the resistivity of the TiN film. The resistivity decrease of the TiN film can enable a reduction of power consumption in the DRAM operation, which offers an aggressive scaling of DRAM capacitors for high-density integration.