This paper examines the correlation between deposition parameters and crystallinity, texture, and etch rate of reactively sputtered c-axis aligned crystalline (CAAC) IGZO films. Both X-ray diffraction and general area detector diffraction (GADDS) showed that crystallinity increases rapidly above 200 • C with simultaneous formation of highly aligned CAAC. Optimal texture with a c-axis alignment and a minimum GADDS full-width-at-half-maximum of 18 • occurred at 250 • C, with c-axis alignment decreasing at higher temperatures to a FWHM of 35 • at 385 • C. Chemical etch rate in 5 vol% HCl was highly correlated to crystallinity, dropping by a factor of ten in CAAC compared to amorphous IGZO; etch rate hence provides a highly sensitive measure of crystallinity.

No abstract

Amorphous InGaZnO4 (a-IGZO) thin film transistors (TFTs) hold great potential for large area and flexible electronics with current research focused on improving the mobility and stability. In this work, we report on properties of IGZO TFTs fabricated using laser spike annealing (LSA) with a scanned continuous wave CO2 laser. For peak annealing temperatures near 430 °C and a 1 ms dwell, TFTs exhibit saturation field-effect mobilities above 70 cm2/V-s (Von ∼ −3 V), a value over 4 times higher than furnace-annealed control samples (∼16 cm2/V-s). A model linking oxygen deficient defect structures with limited structural relaxation after the LSA anneal is proposed to explain the observed high mobility. This mobility is also shown to be comparable to the estimated trap-free mobility in oxide semiconductors and suggests that shallow traps can be removed by transient thermal annealing under optimized conditions.

The influence of deposition parameters on the properties of RF sputter deposited c-axis aligned crystalline (CAAC) IGZO was studied using both single parameter and design of experiment (DOE) analysis (target composition near InGaZnO 4 ). Use of a 3-level, 6 factor Box-Behnken DOE enabled efficient sampling of the large processing parameter space. Deposition temperature and power, oxygen fraction in the sputter gas, and the ensuing Zn composition were identified as the key parameters correlated with c-axis texture in the films. CAAC formation commenced at a deposition temperature of 250 • C reaching maximum surface normal alignment near 315 • C. Crystallinity and alignment increased rapidly with oxygen fraction becoming nearly independent of fraction between 10% and 50%. Zinc loss during deposition at high temperatures and low oxygen partial pressures correlated with lower crystallinity, suggesting a strong composition dependence of CAAC formation in IGZO alloys. In contrast, increased deposition power improved alignment. Optimal deposition conditions were identified and related to a proposed nucleation and growth model.

The influence of deposition parameters on the properties of RF sputter deposited c-axis aligned crystalline (CAAC) IGZO was evaluated using both single parameter and design of experiment (DOE) analysis. Deposition temperature and oxygen partial pressure were found to be primary parameters determining CAAC alignment and crystallinity. CAAC is first formed at a deposition temperature of 185 o C, reaching optimal surface normal alignment at ~315 o C. Crystallinity and alignment increase rapidly with oxygen fraction up to 10%, then becoming nearly independent up to 50%. The Zn fraction and (Ga+Zn)/In ratio were identified as key parameters correlated to c-axis texture in the films. Zinc loss during deposition at high temperatures and low oxygen partial pressures correlated with poor CAAC alignment, while (Ga+Zn)/In ratio approaching an ideal 2.0 ratio exhibited improved CAAC crystallinity. Author KeywordsIGZO, c-axis alignment, thin film, sputtering, design of experiment (DOE).