Study of La-Induced Flat Band Voltage Shift in Metal/HfLaO_x/SiO₂/Si Capacitors

Abstract

The flat band voltage in metal/HfLaO x /SiO 2 /Si capacitors has been investigated as a function of La concentration in HfLaO x . We have found that with an increase of La concentration, the flat band voltage shifts to the negative direction. Furthermore, we demonstrate that the flat band voltage in this system is determined by the La concentration at HfLaO x /SiO 2 interface. This result suggests that the flat band voltage shift is due to the dipole layer formed at the HfLaO x /SiO 2 interface rather than the Fermi-level pinning at the metal/HfLaO x interface.

Improving the electrical characteristics of MOS transistors with CeO2/La2O3 stacked gate dielectric

“…This leaves behind a oxygen vacancy in the dielectric and two electrons fall in the gate Fermi level [18]. However, based on a series of experiments on HfLaO x dielectric films, Yamamoto et al suggested that the flatband shift should not be due to the Fermi level pinning at the HfLaO x /metal interface [19]. In addition, the remote interaction between the Si substrate should also not be the origin for the La-induced V FB shift.…”

“…In addition, the remote interaction between the Si substrate should also not be the origin for the La-induced V FB shift. Instead, the flatband shift should be due to the dipole layer at the high-k/SiO 2 interface [19]. Dipoles can also be formed at the high-k/SiO 2 interfaces as a result of charge exchange between the high-k dielectric and the SiO 2 .…”

Integrations and challenges of novel high-k gate stacks in advanced CMOS technology

“…Recent researches performed in high-k gate stacks indicate that there are interface dipoles at either high-k/gate interface or high-k/substrate interface, depending on the dielectric and gate materials and the process the gate stacks have been proceeded [298,355,356]. Because of the presence of these interfacial dipole in high-k stacks, locating at either high-k/gate interface or high-k/substrate interface, the band alignments will be shifted correspondingly, resulting in the difference between effective work function and the vacuum work function, therefore the effective work functions of metals on dielectric are always different from their vacuum values, posing a significant concern in terms of the controlling of threshold voltage in MOSFETs.…”

“…The modulation of gate effective work function by alien capping layer on high-k or inserted layer below high-k will suffer from the effective oxides thickness (EOT) increasing. Therefore, as an alternative method, the doped high-k or alloyed metal gate can be applied, such as, HfLaO x [356], HfAlO x [361], and MoAlN x [368].…”

Anomalous positive flatband voltage shifts in metal gate stacks containing rare-earth oxide capping layers

“…This shift in our poly-Si capped devices agrees, in direction and magnitude, with previous reports on the effect of lanthanide oxide insertion into high-k/metal gate stacks on V FB . [4][5][6] However, the shift in V FB for devices without the poly-Si overlayer to the right by nearly 450 mV (relative to the poly-Si capped Gd 2 O 3 -contining device) is unexpected. To confirm this unexpected result, we have repeated the experiment three different times, where nearly a hundred devices were measured each time, covering different dielectric compositions and EOTs.…”