Crystallinity and texturing of RF sputtered c-axis aligned crystal InGaZnO 4 (CAAC IGZO) thin films were quantified using X-ray diffraction techniques. Above 190 C, nanocrystalline films with an X-ray peak at 2h ¼ 30 (009 planes) developed with increasing c-axis normal texturing up to 310 C. Under optimal conditions (310 C, 10% O 2 ), films exhibited a c-axis texture full-width half-maximum of 20 . Cross-sectional high-resolution transmission electron microscopy confirmed these results, showing alignment variation of 69 over a 15 Â 15 nm field of view and indicating formation of much larger aligned domains than previously reported. At higher deposition temperatures, c-axis alignment was gradually lost as polycrystalline films developed. V C 2014 AIP Publishing LLC. [http://dx.
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.
Crystallinity and texture of c-axis aligned crystal indium gallium zinc oxide (CAAC IGZO) films deposited by RF reactive sputtering were studied and characterized over a range of deposition conditions. The characteristic CAAC (009) peak at 2θ=30 o was observed by X-ray diffraction, and nanocrystalline domain texture was determined using a general area detector diffraction system (GADDS). Highly ordered CAAC films were obtained near the InGaZnO4 composition at a substrate temperature of 310 o C and in 10% O2. High-resolution transmission electron microscopy (HRTEM) confirmed the formation of CAAC showing 2-3 nm domains aligned over 15 nm x 15 nm fields of view. Cross-section HRTEM of the CAAC/substrate interface shows formation of an initially disordered IGZO layer prior to CAAC formation, suggesting a nucleation mechanism similar to ZnO thin films.
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).
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