Multiple Roles of Hydrogen Treatments in Amorphous In–Ga–Zn–O Films

Abstract

The roles of hydrogen introduced by post-deposition hydrogen treatments were investigated for amorphous In–Ga–Zn–O (a-IGZO) films using room-temperature hydrogen plasma (H-plasma) and high-temperature H2 annealing. It was found that these treatments cause different effects as confirmed by hard X-ray photoemission spectroscopy and difference spectrum analyses. The H-plasma treatment increased both the near-valence band maximum (near-VBM) states (observed just above VBM) and the –OH bonds (confirmed by O 1s core spectrum) if a-IGZO films were deposited under an optimum condition, leading to the conclusion that the room-temperature H treatment incorporates H to a-IGZO films as –OH bonds, and the increase in the relatively shallow near-VBM states (peaked at ∼1.0 eV, extended to ∼2.4 eV from VBM) is ascribed to the generated –OH bonds. On the other hand, high-temperature H2 annealing did not increase the O 1s –OH signal, and its difference spectrum showed a different peak centered at ∼0.7 eV. This difference spectrum is similar to that of H-less a-IGZO films deposited without O2 supply by ultra-high vacuum sputtering and assigned to oxygen deficiency. These results will contribute to control the operation characteristics and the instability issues of a-IGZO TFTs. Further, the deconvoluted difference spectra will be the standard fingerprints of these defects in a-IGZO.