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 Al(2)O(3) blocking oxide with materials with higher dielectric constant kappa, as this would increase the electric field across the tunnel oxide. A possible solution is to integrate rare earth scandates. Among the scandates, DyScO(3) appears as an attractive material due to the reported high-kappa 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 O(3) as oxidizing agent. First, Sc(2)O(3) and Dy(2)O(3) growth process was optimized by changing growth temperature (T(g)) and ALD cycle. The best conditions for the deposition of the ternary DyScO films were found to be T(g)=350 degrees 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 degrees 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 kappa was extracted from capacitance-voltage (C-V) electrical measurements. As deposited amorphous DyScO films on silicon remain amorphous after annealing up to 900 degrees C. Film electron density reduces while thickness increases with annealing, surface roughness remaining at similar to 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 degrees C, in films deposited on Si, as major Si diffusion affects the ternary oxide. Only at 600 degrees C the diffusion phenomena and film composition are preserved. The extracted DyScO dielectric constant is kappa similar to 20 in films annealed at 600 degrees C on Si. When deposited on Si-rich SiN, DyScO uniformity remains well preserved up to 900 degrees C, with an improvement of the thermal stability with respect to deposition on Si. Si diffusion is evident at 1030 degrees C only. The kappa-value extracted from C-V resulted to be kappa similar to 20.