Understanding the Mechanism of Electronic Defect Suppression Enabled by Nonidealities in Atomic Layer Deposition

Abstract

Silicon germanium (SiGe) is a multi-functional material considered for quantum computing, neuromorphic devices and CMOS transistors. However, implementation of SiGe in nano-scale electronic devices necessitates suppression of surface states dominating on electronic properties. The absence of a stable and passive surface oxide for SiGe results formation of charge traps at the SiGe -oxide interface induced by GeO x . In an ideal ALD process in which oxide is grown layer-by-layer, the GeO x formation should be prevented with selective surface oxidation (i.e. formation of an SiO x interface) by controlling oxidant dose in first few ALD cycles of the oxide deposition on SiGe. However, in a real ALD process, the interface evolves during entire ALD oxide deposition due to diffusion of reactant species through the gate oxide. In this work, this diffusion process in non-ideal ALD is investigated and exploited: the diffusion through the oxide during ALD is utilized to passivate the interfacial defects by employing ozone as a secondary oxidant. Periodic ozone exposure during gate oxide ALD on SiGe is shown to reduce the integrated trap density (D it ) across the band gap by nearly an order of magnitude in Al 2 O 3 (< 6×10 10 cm -2 ) and in HfO 2 (< 3.9×10 11 cm -2 ) by forming a SiO x rich interface on SiGe. Depletion of Ge from the interfacial layer (IL) by enhancement of volatile GeO x formation and consequent desorption from the SiGe with ozone insertion during ALD growth process is confirmed by electron energy loss spectroscopy (STEM-EELS) and hypothesized to be the mechanism for reduction of the interfacial defects. In this work, the nanoscale mechanism for defect suppression at SiGe oxide interface is demonstrated which is engineering of diffusion species in ALD process due to facile diffusion of reactant species in non-ideal ALD.

Post-metallization annealing and photolithography effects in p-type Ge/Al2O3/Al MOS structures

“…This partial elimination of the interface traps after PMA has been observed in several studies of p-type Ge MOS capacitors, indicating a universal origin of this effect. 12,15,16,31,32 In the following, we summarize the results of the electrical characterization and their interrelation with the corresponding structural main findings.…”

“…A plausible reconstruction is GeO x desorption, in addition to that caused by the scavenging action of Al gate. 32 This further implies that the GeO x interfacial layer grown during ALD is a defective layer that contains unsaturated bonds which are reflected in D it measurements. This GeO x layer is quite different with the one which is produced by the deliberate Ge reoxidation methods using oxygen plasma, oxygen or ozone.…”

Low Surface Recombination in Hexagonal SiGe Alloy Nanowires: Implications for SiGe-Based Nanolasers

“…The last columns show the surface recombination velocity ( S eff ) as determined on planar cubic germanium and silicon wafers. Surface passivation of cubic SiGe has been investigated by several authors; − however, surface recombination velocities of planar cubic SiGe are still very rarely reported in the literature and are therefore not given in the table. b Note that for cub-Si and cub-Ge the optimum growth conditions for a-Si:H regarding surface passivation are slightly different. c The native oxide is removed in situ by the PO x /Al 2 O 3 deposition process through a self-cleaning effect …”

“…The last columns show the surface recombination velocity ( S eff ) as determined on planar cubic germanium and silicon wafers. Surface passivation of cubic SiGe has been investigated by several authors; − however, surface recombination velocities of planar cubic SiGe are still very rarely reported in the literature and are therefore not given in the table.…”