Atomic Layer Etching of Titanium Nitride With O ₃ and NbCl ₅

Titanium nitride is one of the essential materials in the semiconductor industry. To use this material in new device architectures, selective and well controlled etching methods, both anisotropic and isotropic are needed. Thermal atomic layer etching is an isotropic etching method with high selectivity and control over etch depth. It removes material conformally from high aspect ratio and non‐line‐of‐sight surfaces and in the ideal case can result in smoothing of the etched surface. This study presents an atomic layer etching process based on TiN surface oxidation using O ₃ and etching of the oxide with NbCl ₅ . The process was studied at 200–350°C, and etch per cycle values of 0.5–4.5 Å were observed. Roughness development of the etched films was studied using atomic force microscopy, and it was found that the films remain very smooth. At 200°C, even smoothing of the films was seen. Very little residue was left on the films or on the substrate after fully etching the film. Variation in the resistivity of the etched films was observed, with increasing resistivity for thinner films until about 4 nm thickness, where the resistivity actually decreased.