82
Strain-Engineered MOSFETs
technology when source/drain length increases, and the same modelling
approach is applicable to the TSV-induced thermal stress effect.
With the assistance of the stress model, the impact of TSV thermal stress
on mobility variation may be predicted. Figure 3.20 shows the mobility variation with the distance from the TSV edge. The mobility varies significantly
inside the keep-out zone, while the stays stable out of the keep-out zone. To
keep devices unaffected from the thermal stress, the area of the keep-out
zone is required. More KOZ area reduces the impacts of thermal stress on
devices, ensuring the stable process variation. However, the keep-out zone
can be utilised with a stress-aware design approach if the mobility variation can be well modeled, illustrating the opportunities from a joint devicedesign perspective.
For an arbitrary criterion for KOZ, assuming equivalent to 10% change in
mobility, the area of KOZ surrounding the TSV has been calculated by Lu [19].
The effects of TSV diameter D f and wafer thickness on KOZ are shown in
Figures 3.21(a) and (b), respectively. It is seen that the diameter has a significant effect on the area of KOZ for p-MOSFET, increasing approximately with
the square of D f . Figure 3.21(b) shows that the area of KOZ for p-MOSFET
initially increases with the wafer thickness H, and then reaches a stable value
if the wafer thickness is greater than 5D f .
2
0
200
400
600
Distance from TSV (nm)
800 1000 1200 1400
4
6
8
10
r TSV = 700 nm
t ox = 150 nm
σ m = 1 GPa
12
14
Area
16
1.1
1.0
1.2
1.3
1.4
1.5
1.6
1.7
1.8
TSV Area (µm
2
)
Mobility Enhancement Factor
Mobility enhancement factor
FIGURE 3.20
Trade-off between TSV area and the influence of mobility enhancement factor. (After Wang,
C.-C., Predictive Modelling for Extremely Scaled CMOS and Post Silicon Devices, PhD thesis,
Arizona State University, 2011.)
Strain-Engineered MOSFETs
technology when source/drain length increases, and the same modelling
approach is applicable to the TSV-induced thermal stress effect.
With the assistance of the stress model, the impact of TSV thermal stress
on mobility variation may be predicted. Figure 3.20 shows the mobility variation with the distance from the TSV edge. The mobility varies significantly
inside the keep-out zone, while the stays stable out of the keep-out zone. To
keep devices unaffected from the thermal stress, the area of the keep-out
zone is required. More KOZ area reduces the impacts of thermal stress on
devices, ensuring the stable process variation. However, the keep-out zone
can be utilised with a stress-aware design approach if the mobility variation can be well modeled, illustrating the opportunities from a joint devicedesign perspective.
For an arbitrary criterion for KOZ, assuming equivalent to 10% change in
mobility, the area of KOZ surrounding the TSV has been calculated by Lu [19].
The effects of TSV diameter D f and wafer thickness on KOZ are shown in
Figures 3.21(a) and (b), respectively. It is seen that the diameter has a significant effect on the area of KOZ for p-MOSFET, increasing approximately with
the square of D f . Figure 3.21(b) shows that the area of KOZ for p-MOSFET
initially increases with the wafer thickness H, and then reaches a stable value
if the wafer thickness is greater than 5D f .
2
0
200
400
600
Distance from TSV (nm)
800 1000 1200 1400
4
6
8
10
r TSV = 700 nm
t ox = 150 nm
σ m = 1 GPa
12
14
Area
16
1.1
1.0
1.2
1.3
1.4
1.5
1.6
1.7
1.8
TSV Area (µm
2
)
Mobility Enhancement Factor
Mobility enhancement factor
FIGURE 3.20
Trade-off between TSV area and the influence of mobility enhancement factor. (After Wang,
C.-C., Predictive Modelling for Extremely Scaled CMOS and Post Silicon Devices, PhD thesis,
Arizona State University, 2011.)