Synthesis and characterization of DyScO films deposited on Si and Si-rich SiN by atomic layer deposition for blocking layer replacement in TANOS stack

In the view of improving standard TANOS stacks, a possible route is the replacement of Al2O3 blocking oxide with materials with higher dielectric constant κ, as this would increase the electric field across the tunnel oxide. A possible solution is to integrate rare earth scandates. Among the scandates, DyScO3 appears as an attractive material due to the reported high-κ value. Films with 10–30 nm nominal thickness were grown by atomic layer deposition (ALD) on Si substrates for process optimization and structural characterization. Sc(thd)3 and Dy(thd)3 were used as Sc and Dy precursors and O3 as oxidizing agent. First, Sc2O3 and Dy2O3 growth process was optimized by changing growth temperature (Tg) and ALD cycle. The best conditions for the deposition of the ternary DyScO films were found to be Tg=350 °C and Dy:Sc=1:1 pulsing ratio. Optimized films were also grown on Si-rich SiN for integration as blocking oxide. After deposition, films were subjected to rapid thermal annealing up to 1030 °C to check their thermal stability. Film thickness was checked by x-ray reflectivity, together with roughness and electron density. Film crystallinity was investigated by grazing incidence x-ray diffraction. Film uniformity and thermal stability were explored by time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profiles. Dielectric constant κ was extracted from capacitance-voltage (C-V) electrical measurements. As deposited amorphous DyScO films on silicon remain amorphous after annealing up to 900 °C. Film electron density reduces while thickness increases with annealing, surface roughness remaining at ∼1.5 nm. The measured Sc:Dy atomic ratio by total x-ray fluorescence analyses is 1.33 in the as deposited film. ToF-SIMS depth profiles showed that film uniformity and composition is not preserved at 900 °C, in films deposited on Si, as major Si diffusion affects the ternary oxide. Only at 600 °C the diffusion phenomena and film composition are preserved. The extracted DyScO dielectric constant is κ∼20 in films annealed at 600 °C on Si. When deposited on Si-rich SiN, DyScO uniformity remains well preserved up to 900 °C, with an improvement of the thermal stability with respect to deposition on Si. Si diffusion is evident at 1030 °C only. The κ-value extracted from C-V resulted to be κ∼20.