Deffect profiling in the SiO2/ Al2O3 interface using Variable Tcharge-Tdischarge Amplitude Charge Pumping (VT2ACP)

A Variable T
charge
-T
discharge
Amplitude Charge Pumping (VT
²
ACP) is used to profile defect in the SiO
2
and Al
2
O
3
separately in Flash Memory based devices. It is shown that by independently controlling the pulse low timing “discharging time” and high level timing “charging time”, the contribution of interface and bulk Al
2
O
3
traps can be separated. By using the ellipsometry and the measured intersection time t
charge
to trap in the high- k (∼60 μs), SiO
2
thickness of 0.87 nm and scanning rate of 0.19nm/dec is found. Using a slanted wafer, the result shows that in the case of thin SiO
2
(∼1nm) the trap density close to the substrate (short t
charge
) is one order of magnitude higher compared to thick SiO
2
(∼3nm). For t
SiO2
= 1.7nm all traps are in the SiO
2
or SiO
2
/Al
2
O
3
transition layer. Only for the thickest SiO
2
layers (2.7 and 3 nm) the trap density becomes low and constant. Additionally WKB-approximation is used to calculate the filling probability of the traps (f
T
), the modeled scanning rate nearly doubles to ∼0.29 nm/dec and 0.27 nm/dec for amorphous and crystalline, respectively. In summary, the method of trap energy/depth profiling by using VT
²
ACP allows scanning from ∼0.5nm up to 1.2nm in depth and 0.1 to 0.7eV in energy range above the E
c
^Si
band depending on sample used. The results show that there exist significant interaction between SiO
2
and Al
2
O
3
when processed with PDA 1000°C. For amorphous Al
2
O
3
(PDA 700°C) the impact of the precursor is not reflected in the SiO
2
trap density while for crystalline Al
2
O
3
no increase in trap density at 0.3eV above the E
c
^Si
band is observed.