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 $∼1.5nm$⁠. 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 $κ∼20$⁠.