We investigated roles of hydrogen on physical properties of a-IGZO films and thin-film transistors (TFTs) by comparing standard and ultra-high vacuum (UHV) sputtering systems. It was confirmed that the impurity hydrogens come mainly from the residual gas in the deposition chamber and the molecules adsorbed to the surface of the sputtering target. It was found impurity hydrogen has unfavorable effects as follows; (i) enhances selective Zn desorption during film deposition, and (ii) weakens chemical bonds of the resulting film, causing temperature instability. On the other hand, the UHV a-IGZO films with less hydrogen had low density and exhibited structural instability, suggesting that some hydrogens would have a favorable effect to enhance structural relaxation rate and to form denser and more stable structures during film deposition at room temperature. The revealed hydrogen effects are discussed in relation to those in amorphous silicon and silicon dioxide.Amorphous oxide semiconductors represented by amorphous InGa-Zn-O (a-IGZO) have superior properties for thin-film transistors (TFTs) such as large electron mobilities > 10 cm 2 /(Vs), good uniformity, stability, and low-temperature fabrication process; 1 therefore, a-IGZO TFTs are used in large-area, high-resolution and/or highframe rate liquid-crystal displays (LCDs) and organic light-emitting diode displays (OLEDs). Although the high mobility is obtained for a-IGZO TFTs even fabricated at room temperature (RT) without thermal treatments, post-deposition thermal annealing e.g. at 300-400 • C is required to obtain satisfactory good uniformity and stability. [2][3][4][5] In particular, addition of appropriate amount of water in the annealing atmosphere produces further improved TFTs (wet O 2 annealing). 6 It is reported that the wet O 2 annealing reduced donor states and weak oxygen-metal chemical bonds, 6,7 the latter of which was confirmed by suppressed desorption of H 2 O and metal-related species in a lowtemperature region 100-300 • C. Unexpectedly, it also revealed that the wet O 2 annealing suppressed desorption of hydrogen although the wet O 2 annealing uses H 2 O in the annealing atmosphere. It has also been reported that a-IGZO films contain high-density impurity hydrogens at 10 20 -10 21 cm −3 , which exist mainly as -OH groups. 8,9 On the other hand, it has also been reported that post-deposition hydrogen treatments (e.g., thermal annealing in a hydrogen-containing atmosphere, 10 hydrogen plasma, 11-13 and proton implantation) 14 generate shallow donor states and increase free electrons and electronic conductivity, which is supported also by theoretical calculations; 15 therefore, hydrogen treatments e.g. by subsequent deposition of aSiN x :H have been proposed to fabricate co-planar and self-alignment structure TFTs. 11 To explain these results, we proposed a model that the impurity hydrogens in unannealed a-IGZO would work as shallow donors, but the generated free electrons are trapped and compensated by excess oxygens introduced during film depos...

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Origin of constant positive gate bias stress instability in amorphous In-Ga-Zn-O thin-film transistor is studied. Threshold voltage shift ( V th ) during the stress test exhibits two different behaviors: 1) a power function-type and 2) a logarithmic function-type depending on thermal treatment atmosphere and temperature. Thermal desorption spectroscopy indicated that the V th behavior changes from the log-function type to the power-function type as the amount of H 2 desorption increases. Furthermore, the recovery behavior of V th was not affected by gate bias. These results are explained by a diffusionlimited process of neutral hydrogen, which occurs within 2 nm in the vicinity of the channel-insulator interface.Index Terms-Amorphous In-Ga-Zn-O, thin-film transistor, threshold voltage instability, dry annealing, wet annealing, hydrogen desorption.

Epitaxial growth of 4H-SiC on 150 mm wafers with the recombination-enhancing buffer layer was studied. In order to accomplish the reduction of basal plane dislocations in the buffer layer to almost free level and assure its quality in production, non-destructive evaluation using photoluminescence method was investigated. Epitaxial wafers of which the buffer layer and the drift layer have more than 99% BPD free area in a 2.6 mm × 2.6 mm block evaluation were realized by optimizing the epitaxial growth conditions. Furthermore, very low surface defects density and excellent thickness and doping uniformity were achieved simultaneously.

Epitaxial growth of 4H-SiC on 150 mm wafers using 3 x 150 mm multi-wafer CVD has been investigated to realize extremely low defect density on the epitaxial layer in order to achieve stable fabrication of high current devices with large die size. By optimizing the epitaxial growth conditions as well as the improved procedures for the inside the furnace to remain cleaned stably for cumulative growth processes, we have demonstrated an extensive 99% defect free epitaxial inlayer in a 5 mm x 5 mm block evaluation which is having excellent doping and thickness uniformity simultaneously.