214
Strain-Engineered MOSFETs
Stress distribution from source to drain regions of 45 nm n-MOSFETs for different cap layer thicknesses are shown in Figure 7.7. As shown in Figure 7.7(a),
the cap layer thickness increase results in higher tensile ε xx stress in the channel region. Tensile stress is larger at the centre of the channel. Figure 7.7(b)
shows the ε yy component stress distribution. The variation of channel stress,
both ε xx and ε yy , with nitride thickness is shown in Figure 7.8. Figure 7.9 shows
0.5
Tensile Strain ε xx
Compressive Strain ε yy
Caplayer ickness (μm)
0.4
0.3
0.2
0.1
0.0
–0.1
–0.2
0.05
0.10
0.15
0.20
0.25
0.30
Channel Stress ε
xx (GPa)
FIGURE 7.8
Effect of increasing silicon-nitride thickness on channel stress components in n-MOSFETs.
Caplayer thickness
Caplayer thickness
45 nm
75 nm
100 nm
200 nm
Caplayer thickness
200 nm
Caplayer thickness
100 nm
X component of
stress ε xx
Y component of
stress ε yy
400
350
300
150
100
250
200
50
0
–50
–100
–0.2
–0.3
–0.1
0
X-Coordinate (um)
(a) nMOS
0.1
100
50
0
–50
–100
–150
–200
–100
0.3
0.2
–0.2
–0.3
–0.1
0
X-Coordinate (um)
(b) nMOS
0.1
0.2
0.3
Channel Stress (MPa)
Channel Stress (MPa)
FIGURE 7.7
Effect of increasing silicon-nitride thickness on channel: (a) lateral stress ε xx components and
(b) vertical stress components ε yy .