Molecular-beam Deposition of High-k Gate Dielectrics for Advanced CMOS

Summary

Advanced high-κ gate dielectric stacks directly deposited on Si or high mobility semiconductors such as Ge by MBE may offer the solution for aggressive scaling of future nanoelectronic devices. A new high-k dielectric, the pyrochlore La₂Hf₂O₇, has been systematically investigated. This material can be prepared on Si(001) in a cube-on-cube epitaxial mode at high temperature around 770°C forming ultimately clean interfaces with the substrate. At lower temperature the material is amorphous having leakage current four to five orders of magnitude lower than conventional SiO₂ with the same equivalent oxide thickness (EOT) of about 1 nm. Further scaling is expected to be difficult since only moderate values of the dielectric permittivity k around 18 can be obtained. On the other hand, HfO₂ prepared by MBD on Ge(001) substrates forms sharp interfaces and has a relatively high κ∼25 which is close to the expected bulk value. Low EOT values around 0.75 nm have been obtained at very low leakage current of 4.5 × 10⁻⁴ A/cm² at 1 V in accumulation. The observed low frequency behaviour of the high frequency (i.e 1 kHz) C-V curves in inversion was attributed to the high intrinsic carrier concentration in Ge due to the small energy band gap.