Cycle time effects on growth and transistor characteristics of spatial atomic layer deposition of zinc oxide
(Color online) (a) Schematic of the SALD head, showing the surface region that corresponds to a full ALD cycle. Shaded segments (red and blue on-line) correspond to reactive precursors, while the neighboring boxed segments are the inert purge gas. (b) An expanded view of one source and exhaust channel, with parabolic gas flow and entrainment illustrated.
(Color online) ZnO growth per cycle as a function of temperature for different pulse/purge times. The temperature at which each curve peaks depends upon the length of the cycle. The partial pressures of DEZn and H2O were 310 and 200 mT, respectively, for the data shown in this paper.
(Color online) ALD saturation curve for ZnO at 150 and 200 °C. In the solid and dashed curves, pulse/purge times are matched. The diamonds represent points that have precursor exposures of 2000 ms each and are plotted according to the length of the (matched) purge time.
(Color online) Sheet resistance as a function of pulse/purge time for 100-nm-thick ZnO layers grown at 150 and 200 °C, and also as grown at 200 °C with N-doping. All conditions show a decrease in resistance with increased pulse/purge time.
(Color online) Log of drain current vs gate voltage for TFTs grown at 200 °C with varying pulse/purge time for the ZnO. For all data Vd = 0.25 V, L = 47 μm, W = 400 μm, and t ox = 50 nm. (a) Without doping, (b) doped with nitrogen.
(Color online) Differential mobility extracted at Vg − V th = 14 V for TFTs grown with a range of pulse/purge times. The 200 °C data are from devices both with and without N-doping in the ZnO. The 150 °C TFTs were with undoped ZnO. Each data point represents an average taken from over 150 TFTs.
(Color online) XRD 2-theta scan over two 30-nm-thick ZnO layers, one grown with 25 ms pulse/purge and the other with 2000 ms pulse/purge. While overall showing similar polycrystallinity, the longer exposure time corresponds to a higher (002) peak, and relatively little contribution from (100) and (101) side peaks.
Effect on GPC and on resistivity of varying the purge time after exposure to 2 s of DEZn or water, at 200 °C.
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