Slow Trap Properties and Generation in Al₂O₃/GeO_x/Ge MOS Interfaces Formed by Plasma Oxidation Process

Abstract

For realizing Ge CMOS devices with a small equivalent oxide thickness (EOT) and a low density of fast interface states (D it), understanding of slow traps in Ge gate stacks and reduction of its density are one of the most crucial issues. For this purpose, we examine slow trap density and locations of Al2O3/GeO x /Ge MOS gate stacks, which are fabricated by plasma oxidation in this work. In Al2O3/GeO x /Ge MOS interfaces formed by preplasma oxidation (pre-PO) and postplasma oxidation (post-PO), slow trap density has been compared. Also, the slow trap density on the thickness dependence of GeO x and Al2O3 is systematically evaluated for the Al2O3/GeO x /Ge MOS gate stacks formed by pre-PO. It is found that near the conduction band edge of Ge, additional electron slow traps will be generated by using the post-PO process. Above all, in the Al2O3/GeO x /Ge MOS interfaces with pre-PO. The main slow traps can be located near the GeO x /Ge interfaces for the electrons and the Al2O3/GeO x interfaces for the holes, respectively.

Surface passivation of germanium by atomic layer deposited Al2O3 nanolayers

“…6b), an effect that can be attributed to enhanced diffusion of the oxygen species through the GeO x . In contrast to some earlier reports [27,29,62], this increasing GeO x interlayer with substrate temperature did not result in better surface passivation (Fig. 2).…”

“…ALD Al 2 O 3 is a known passivation layer for germanium (Ge) where it is mainly explored for application in MOSFETs [9,[26][27][28][29][30]. ALD of Al 2 O 3 as passivation layer on Ge has been shown to lead to the formation of a germanium oxide (GeO x ) interlayer [27,31,32], somewhat similar to the SiO x interlayer formed by ALD Al 2 O 3 on Si.…”

“…Most research with respect to ALD Al 2 O 3 on Ge was therefore aimed at understanding and engineering the GeO x layer between Ge and Al 2 O 3 [29-31, 39, 41-43]. It has been reported that D it can be lowered by a factor 10 to 100 by addressing this interlayer [26,29,30]. Especially plasma postoxidation of the Ge/Al 2 O 3 stack has proven successful ( D it ≤ 10 11 cm −2 eV −1 ) [26].…”

Trap Reduction through O3 Post‐Deposition Treatment of Y2O3 Thin Films Grown by Atomic Layer Deposition on Ge Substrates

“…The TMA treatment was carefully controlled to decrease the GeO bond density but increase the AlO bond density at the interface. [ 18 ] In another report on Y 2 O 3 film on n‐type Ge substrate, the film was annealed under the O 2 atmosphere for 10 min at 550 °C. By such O 2 annealing, a stable GeO 2 layer can be formed at the interface, and the defect density in the Y 2 O 3 film also decreased.…”

Atomic Layer Densification of AlN Passivation Layer on Epitaxial Ge for Enhancement of Reliability and Electrical Performance of High-K Gate Stacks

“…The presence of GeO x at the oxide/Ge interface suffers severely from the low conduction-band offset and the poor thermal stability . The diffusion of unstable interfacial GeO x into the high-K gate oxide at the process temperatures higher than 420 °C results in significant degradation of the device performance. , Thus, the interface passivation methods based on high-quality Ge oxides, Al 2 O 3 , oxynitride, and rare-earth oxides have been proposed and developed to attain stable oxide/Ge interfaces. − However, because oxygen is involved in these interface passivation methods, it is difficult to completely suppress the formation of unstable GeO x at the interface. In particular, the presence of interfacial GeO x is very critical to the reliability of Ge nMOSFET due to the high density of oxygen vacancies/interface traps at the energy levels near the Ge conduction band …”