Combining Experimental and DFT Investigation of the Mechanism Involved in Thermal Etching of Titanium Nitride Using Alternate Exposures of NbF₅ and CCl₄, or CCl₄ Only

Abstract Thermally activated chemical vapor‐phase etching of titanium nitride (TiN) is studied by utilizing either alternate exposures of niobium pentafluoride (NbF₅) and carbon tetrachloride (CCl₄) or by using CCl₄ alone. Nitrogen (N₂) gas purge steps are carried out in between every reactant exposure. Titanium nitride is etched in a non‐self‐limiting way by NbF₅–CCl₄ based binary chemistry or by CCl₄ at temperatures between 370 and 460 °C. Spectroscopic ellipsometry and a weight balance are used to calculate the etch per cycle. For the binary chemistry, an etch per cycle of ≈0.8 Å is obtained for 0.5 and 3 s long exposures of NbF₅ and CCl₄, respectively at 460 °C. On the contrary, under the same conditions, the etch process with CCl₄ alone gives an etch per cycle of about 0.5 Å. In the CCl₄‐only etch process, the thickness of TiN films removed at 460 °C varies linearly with the number of etch cycles. Furthermore, CCl₄ alone is able to etch TiN selectively over other materials such as Al₂O₃, SiO₂, and Si₃N₄. X‐ray photoelectron spectroscopy and bright field transmission electron microscopy are used for studying the post‐etch surfaces. To understand possible reaction products and energetics, first‐principles calculations are carried out with density functional theory. From thermochemical analysis of possible reaction models, it is found that NbF₅ alone cannot etch TiN while CCl₄ alone can etch it at high temperatures. The predicted byproducts of the reaction between the CCl₄ gas molecules and TiN surface are TiCl₃ and ClCN. Similarly, TiF₄, NbFCl₃, and ClCN are predicted to be the likely products when TiN is exposed to both NbF₅ and CCl₄. A more favorable etch reaction is predicted when TiN is exposed to both NbF₅ and CCl₄ (ΔG = −2.7 eV at 640 K) as compared to exposure to CCl₄ only (ΔG = −2 eV at 640 K) process. This indicates that an enhanced etch rate is possible when TiN is exposed alternately to both NbF₅ and CCl₄, which is in close agreement with the experimental results.