Passivation role of sulfur and etching behavior in plasma etched TiW using SF₆ and BCl₃ gases

TiW is an effective diffusion barrier between Si substrate and various metals. In particular it prevents the hillock formation and junction spiking associated with Al-metallization. However, the complexity of the plasma chemistry for TiW etching makes it difficult to explain the etching behavior. Reactive ion etching of TiW was performed to explain the role of sulfur on etching behavior using SF₆ and BCl₃ gases with various mixing ratios. The surface state of etched TiW was analyzed using X-ray photoelectron spectroscopy and the formation of metal-S bonds was found after etching with the plasma gases containing SF₆. These bonds are shown to prevent oxidation of the etched TiW surface, especially Ti, during exposure to air. The etch rate decreased as the mixing ratio of BCl₃ gas increased and was almost zero with BCl₃ only. Sulfur could promote the etch rate by surface cleaning and removal of native oxide.