Defects in the interfacial layer of SiO2-HfO2 gate stacks: Depth distribution and indentification

The defects in the SIO
₂
interfacial layer (IL) in SiO
₂
-HfO
₂
gate stacks are studied using charge pumping (CP). To that aim, conventional CP curves and interface trap density vs. energy, D
_it
(E), profiles measured on these devices are compared with those recorded from state of the art (S-A) MOSFETs. By doing so, specific features in the results recorded from the devices with HfO
₂
are pointed out. Then, trap depth concentration, N
₁
(x), profiles, recorded from the Si- SIO
₂
interface towards HIO
₂
are reported. With regard to S-A MOSFETs, these profiles provide evidence of 1) a strong increase in N, towards HfO
₂
, 2) an impact of HfO
₂
on the trap properties up to the Si-SiO
₂
interface, and 3), a large increase in the minimum N, value. As the SiO
₂
-HfO
₂
interface is probed for the devices annealed at the lowest temperature, T
_A
, the profiles show a continuous increase of N
_t
from SiO
₂
to HfO
₂
. Then, the impacts on the trap profiles of both T
_A
, and the HfO
₂
thickness deposited, d
_HfO2
, are dealt with. A higher T
_A
yields SIO
₂
re-growth. This 1) pushes the increase of Nt observed towards HIO
₂
further away from the Si-SiO
₂
interface but 2) yields also to a deeper penetration of this increase in the IL. The first effect dominates. Also, it seems that increasing d
_HfO2
slightly increases the trap penetration into the IL. Finally, the two states of the P
_bo
center are identified in the trap depth concentration profiles. Their characteristics differ from those in S-A MOSFETs. They are correlated for the first time in fresh and fully processed devices with the interface trap densities measured in both parts of the silicon bandgap. By adjusting the experimental conditions, the N
₁
(x) profiles corresponding to the two P^ center levels can be drawn.