Dielectric Properties of Thermal and Plasma-Assisted Atomic Layer Deposited Al[sub 2]O[sub 3] Thin Films

Abstract

A comparative electrical characterization study of aluminum oxide ͑Al 2 O 3 ͒ deposited by thermal and plasma-assisted atomic layer depositions ͑ALDs͒ in a single reactor is presented. Capacitance and leakage current measurements show that the Al 2 O 3 deposited by the plasma-assisted ALD shows excellent dielectric properties, such as better interfaces with silicon, lower oxide trap charges, higher tunnel barrier with aluminum electrode, and better dielectric permittivity ͑k = 8.8͒, than the thermal ALD Al 2 O 3 . Remarkably, the plasma-assisted ALD Al 2 O 3 films exhibit more negative fixed oxide charge density than the thermal ALD Al 2 O 3 layers. In addition, it is shown that plasma-assisted ALD Al 2 O 3 exhibits negligible trap-assisted ͑Poole-Frenkel͒ conduction unlike the thermal ALD Al 2 O 3 films, resulting in higher breakdown electric fields than the thermal ALD prepared films.Among various metal oxides with medium dielectric permittivity, Al 2 O 3 has been proposed as a promising and reliable candidate as an initial replacement for the conventional silicon oxide ͑SiO 2 ͒ as a gate oxide material in metal-oxide-semiconductor transistors because of its higher dielectric permittivity of ϳ8-9, low leakage current level, and high breakdown electric fields due to its large bandgap ͑8.8 eV͒. 1-3 Al 2 O 3 is known for its large band-offset with silicon, which is crucial for achieving low leakage currents through the devices. 4 Moreover, Al 2 O 3 has an excellent thermal and chemical stabilities, for instance, it remains amorphous until temperatures above 800°C. 5 Upon using atomic layer deposition ͑ALD͒, reactive chemistries can be used which ensure very good chemisorption and growth behavior on various substrates at low deposition temperatures. 3 It has been reported that Al 2 O 3 can be deposited on silicon with very small interfacial oxide layer thickness compared to other high-k oxides, 6 which makes it useful as an oxidation-barrier for the ALD processing of other high-k layers as well. 7 More than as a gate oxide, Al 2 O 3 is an important material for numerous application domains, for instance, to enhance the quantum efficiency of silicon in metal-insulator-semiconductor devices, 8,9 to encapsulate materials and devices that are sensitive to environments such as humidity, to enhance the Q-factor of silicon cantilevers, 10,11 to enable functionalization on hydrophobic graphene and carbon nanotube surfaces for the applications in nanoelectronics, 12,13 and to passivate surfaces of silicon solar cells. 14 Remarkable about ALD processed Al 2 O 3 is that the oxide can contain intrinsic negative fixed oxide charges 14 that are beneficial for the applications in charge-trap flash memory devices 15 and, in particular, high-efficiency silicon solar cells. 16,17 With the added value of ALD achieving good conformality in the high aspect-ratio features, high capacitance density metal-insulator-metal ͑MIM͒ capacitors have been realized for the integration of passive elements. 18,19 In this paper, we compare the dielec...

Quantum‐Tunneling Metal‐Insulator‐Metal Diodes Made by Rapid Atmospheric Pressure Chemical Vapor Deposition

“…Correspondingly, the AP‐CVD diodes demonstrated superior asymmetry and nonlinearity at 1.4 V in Figure b,c when the conduction mechanism changed from Poole–Frenkel to Fowler–Nordheim tunneling at the turn on voltage. These results indicate that the insulator deposition method has an impact on the barrier height and MIM diode properties, consistent with previous reports …”

“…These barriers are illustrated schematically in the insets of Figure . The forward Al 2 O 3 –Al barrier heights of 2.20 and 2.80 eV observed in the AP‐CVD and PEALD diodes, respectively, are consistent with previously reported values of 2.25 and 2.47 ± 0.36 eV that were obtained theoretically and a value of 2.0 ± 0.2 eV obtained from photoemission studies . The lower barrier height observed for the AP‐CVD diodes in this work is consistent with a previous study that indicated that thermal ALD of Al 2 O 3 , which is similar to the AP‐CVD process used here, resulted in a barrier two times smaller than that obtained with PEALD .…”

“…To understand the performance observed for the AP‐CVD diodes, the I–V curves are fitted to three different conduction mechanisms: Poole–Frenkel and Schottky emission for the low voltage range and Fowler–Nordheim tunneling for the high voltage range, in‐line with the appearance of these mechanisms in Al 2 O 3 films in previous reports . This allows the dominant conduction mechanisms for the AP‐CVD and PEALD diodes to be identified.…”

Highly transparent low capacitance plasma enhanced atomic layer deposition Al2O3-HfO2 tunnel junction engineering

“…12 This means that in addition to the removal of -CH 3 group by oxygen radicals, which happens during the first 20 s of exposure, the extended exposure may have formed a denser and amorphous Al-O-Al network, which is in agreement with the O/Al ratio. 13 Currents for Al 2 O 3 and HfO 2 films were plotted versus applied voltage in Figs. 2(a) and 3(a).…”

Ellipsometry and XPS comparative studies of thermal and plasma enhanced atomic layer deposited Al2O3-films

“…However characterizations based X-ray photoelectron spectroscopy (XPS) in dependence of the substrate temperature are not shown in that reviews. Furthermore to our knowledge there seems to be a lack in reports about dielectric parameters in dependence of the substrate temperature for PE-ALD as mostly comparisons are given at fixed temperatures [1,21] or only for T-ALD samples [22]. …”