Formation and texture of Y silicides in annealed TiN/Y thin films on Si substrates☆

Abstract

Yttrium (Y) is a promising candidate for low-resistance NMOS contacts due to the low n-type Schottky barrier height of its silicide and its high charge carrier effective mass. However, previous attempts to achieve a low contact resistivity have failed because of severe oxygen contamination during sputter deposition. This study therefore investigates Y silicide formation in sputtered TiN/Y stacks on Si(001), Si(110), and Si(111) substrates. Upon annealing, hexagonal YSi1.7 forms through a three-step process: (i) metallic Y reacts with Si by solid-state amorphization (SSA), producing amorphous a-YSi, (ii) a-YSi crystallizes into hexagonal YSi1.7 at the interface with Si and (iii) grows in thickness until the reaction is fully completed. X-ray diffraction pole figure analyses confirm epitaxial texturing, with Si(001) and Si(111) exhibiting a single epitaxial component. Consistent with a nucleation-controlled formation, hexagonal YSi1.7 starts to form at a significantly lower temperature on Si(111) compared to Si(001) and Si(110) due to the superior YSi1.7/Si epitaxial relationship. The formation of pinholes during crystallization further supports nucleation-limited formation but results in a partial oxidation of the Y film. These findings clarify the role of nucleation and diffusion during YSi1.7 formation and highlight the challenges that must be addressed should Y be integrated in CMOS devices.