Effects of working pressure and annealing on bulk density and nanopore structures in amorphous In–Ga–Zn–O thin-film transistors

Abstract

Microstructures of amorphous In–Ga–Zn–O (a-IGZO) thin films of different densities were analyzed. Device-quality a-IGZO films were deposited under optimum conditions, e.g., the total pressure P tot = 0.55 Pa produced high film densities of ∼6.1 g/cm3, while a very high P tot = 5.0 Pa produced low film densities of 5.5 g/cm3. Both films formed uniform high-density layers in the vicinity of the glass substrate, 10–20 nm in thickness depending on P tot, while their growth mode changed to a sparse columnar structure in thicker regions. X-ray reflectivity and in situ spectroscopic ellipsometry provided different results on densification by post deposition thermal annealing; i.e., the latter has a higher sensitivity. High-Z-contrast images obtained by high-angle annular dark-field scanning transmission electron microscopy were also useful for detecting nanometer-size non uniformity even in device-quality a-IGZO films.

Electronic Defects in Amorphous Oxide Semiconductors: A Review

“…In addition, high‐angle‐annular‐dark‐field mode of scanning transmission microscopy (HAADF‐STEM) can provide a high‐sensitivity technique for observing microstructures in AOSs because its contrast is proportional to the square of the atomic number, Z 2 and sensitive to the electron density. As seen in Figure , the optimum P TOT = 0.55 Pa provides a high density of 6.1 g cm −3 (≈5% lower than that of crystalline InGaZnO 4 ) while a high P TOT = 5.0 Pa yields a much lower density of 5.5 g cm −3 in the as‐deposited states up to 500 °C annealing. The increase in the density at >500–600 °C is attributed to crystallization, as explained above.…”

“…Note that the structural relaxation depends on the as‐deposited states. While HQ film (i.e., deposited at the optimum condition and has a high film density) shows no detectable relaxation up to 400 °C, LQ films (off‐optimized conditions and low film density) start to relax from very low temperatures, for example, 100 °C, as shown in Figure . Probably related to this structural relaxation behavior, the crystallization onset temperature ( T X ) for AOS also depends on the deposition condition and structure, as shown in Figure .…”

“…a) Film density as a function of annealing temperature for P TOT = 0.55 and 5.0 Pa. b) Total amounts of desorption molecules from a‐IGZO films as a function of P TOT . c,d) Transfer curves of a‐IGZO TFTs for unannealed and 300 °C‐annealed deposited at (c) P TOT = 0.55 and (d) 5.0 Pa. Reproduced with permission . Copyright 2017, IOP Publishing.…”

“…Cross‐sectional HAADF‐STEM images for a‐IGZO films deposited at (a) P TOT = 0.55 Pa (high‐density film) and (b) 5.0 Pa (low‐density film). Reproduced with permission . Copyright 2017, IOP Publishing.…”

Transition Metal‐Doped Amorphous Oxide Semiconductor Thin‐Film Phosphor, Chromium‐Doped Amorphous Gallium Oxide

“…The film densities extracted from the spectra are summarized in the inset of Figure (a). The high film density ( ρ ) > 5.1 g cm −3 was kept up to P O2 = 10 Pa while film density sharply decreased at higher P O2 ; e.g., the high P O2 of 15 Pa resulted in 13% lower density than that of 5 Pa film, indicating that the film deposited at high P O2 ≥ 15 Pa has a porous and defective structure . In order to analyze the impurity species in a ‐GO:Cr x films, we measured TDS for O 2 and H 2 O desorption, which would form recombination centers such as weakly bonded oxygen and hydrogen (Figure (b)).…”