Atomic mechanism of flat-band voltage shifts by La2O3 and Al2O3 in gate stacks

Abstract

The origin of the flat-band voltage shifts for La- and Al-based oxide capping layers in high k metal gate stacks is studied by ab initio calculations on atomic models. Substitutional La, Al, Sr, and Nb at the HfO2–SiO2 interface create dipoles, which shift the flat band voltage in the experimentally observed direction, negative for La and Sr and positive for Al and Nb. The shift does not correlate with the metal’s valence, being opposite for La and Al, which rules out a vacancy model. The shift does correlate with the metal electronegativity/work function. It does not correlate with oxygen ion density, as this is not varied.

Dielectric dipole mitigated Schottky barrier height tuning using atomic layer deposited aluminum oxide for contact resistance reduction

“…12 This may be an intrinsic problem using these dielectrics as differences in screening from abrupt changes in dielectric permittivity are believed to also play a role in the formation of the interface dipole. 33,34 Therefore, another promising alternative is to use different dielectrics with larger interface dipoles and/or with smaller band-offsets such as TiO 2 . 12 Since dielectric permittivity and band gap are often inversely related, very high-j dielectrics such as SrTiO 3 may also prove promising if the interface dipole is found to be large due to the smaller band gap (and smaller tunnel barrier) associated with these dielectrics.…”

Band alignment at the SiO2/HfO2interface: Group IIIA versus group IIIB metal dopants

“…Sharia reported that substitution of Si with Al at the interface results in a smaller VBO [19]. They attribute the effect to the reduction of the interface screening to increasing density of oxygen vacancies caused by the Al [20] applied the image charge model to the SiO 2 /HfO 2 interface making the electrostatic arguments in an attempt to explain the effect of La doping. However, the applicability of this approach is not clear since the screening mechanism in the high k-materials is different from that in the metals.…”

“…Recently, the atomic structure of and band alignment at the un-doped and doped SiO 2 /HfO 2 interfaces have been studied theoretically by several groups using density functional theory (DFT) [18][19][20][21]. Sharia et al considered the un-doped [18] and Al-doped [19] SiO 2 /HfO 2 gate stacks.…”

“…For the Al-doped stack, it was found that Al prefers to substitute for Si rather than Hf, and that Al doping lowers the valence band offset. Robertson et al [20,21] The most important aspect of the SiO 2 /HfO 2 interface in the context of the effective work function is the microscopic picture of the band alignment. It was argued [18] that the dipole correction to the Schottky limit at the SiO 2 /HfO 2 interface can be split in two contributions: charge "spreading" across the interface and screening of this charge by polarizable oxygen ions.…”

Al 2 O 3 / NbAlO / Al 2 O 3 sandwich gate dielectric film on InP

“…Al 2 O 3 has widely used as blocking layer or capping oxide layer due to its wide gap and good thermal stability and easy introduction interface dipoles. 6 Nb 2 O 5 with a high permittivity of 50 was usually used in memory application. 7 film was signed as S2.…”