Al2O3/Si0.7Ge0.3(001) & HfO2/Si0.7Ge0.3(001) interface trap state reduction via in-situ N2/H2 RF downstream plasma passivation

A novel method for passivating the interface between Si0.7Ge0.3 using an in-situ downstream RF plasma consisting of a nitrogen-rich mixture of H-2 and N-2 gases at 250 degrees C prior to atomic layer deposition (ALD) of Al2O3 and HfO2 was demonstrated. XPS spectra of the interface with Al2O3 indicated the presence of a nitride layer enriched in SiONx and depleted in Ge relative to the substrate. The electrical properties of this interface were characterized using I-V and variable frequency C-V measurements of MOS capacitors. The N-2/H-2 plasma passivation process produced a reduced density of interface trap states (D-it) and lower gate leakage compared with ex-situ HF clean and sulfur passivation for Al2O3 gate oxides. The lowered leakage current and Dit observed compared with HF(aq) or sulfur-passivated surfaces were consistent with enhanced oxide nucleation due to N-2/H-2 plasma passivation lowering carbon surface contamination and dangling bonds. TEM/EELS analysis of the interface was consistent with the presence of a thin interfacial nitride layer suppressing the formation of Ge-O bonds at the interface to form an SiOx-rich interlayer (IL).