In this thesis, we demonstrate the process strained silicon (PPS) induced stress distribution by the TCAD simulation. From stress induced energy level change, the mobility shift gives us another way to determine the stress in PMOS structure. Both of two methods tell us that the narrow device or a short gate to STI spacing (A) can provide enough evidence to make sure more increasing on the magnitude of the compressive stress.
By the Id/gm noise fitting method, we can extract the trap density and scattering factor. In the channel length direction, the experiment shows the STI induced stress can give more traps. However, in channel width direction, the large variation of the average trap density comes from the edge structure difference between the middle part. The I-V measurement also gives us the stress on narrow device is not the only reason for mobility change. Inverse narrow channel effect in Vth and mobility would be considered as the plausible origins for the narrow device. When we fabricate the narrow devices to increase the device number per area for cost-down, considering behavior of the narrow device in terms of the mobility, trap density, and Scattering factor should all be taken into account.
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Fig.1 the Energy band diagram illustration of a PMOSFET biased near the threshold point
Fig2 A schematic description of the charge distribution in the MOS structure.
Fig.3The schematic illustration of oxide traps exchange with the channel carriers causing a fluctuation in the surface potential.
Fig4The band diagram describe the tunneling transitions, (i) directly [7]
or (ii) using interface traps as stepping stones [8] from the Si to gate oxide
Fig.5 The STI structure induced stress in channel width (W) and channel length direction (L).
Device Structure
Channel Length L
Channel Width (W)
Gate to STI Spacing A
Surrounding STI Stress
Surrounding STI Stress
Surrounding STI Stress Surrounding STI Stress
Gate
Bulk Drain
Source
Fig.6The difference between id/gm and Vg-Vth fitting method. We can see that Vg-Vth is a straight line, instead id/gm is a curve .
0.2 0.3 0.4 0.5 0.6 0.7
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
ID/gm (V)
Vg (V) ID/gm by Ueff
Vg-Vth
ID(Vd=0.025)/gm ID(Vd=0.1)/gm
ID/gm BY Noise Extraction
ID/gm by Ueff Consider M*ID^2/2 Effect
Fig.7 Two different fitting method (Vg-Vth, Id/gm) on the same sample.
0.0 0.1 0.2 0.3 0.4 0.5 0.6
0.000001 0.000002 0.000003 0.000004 0.000005
Svg^0.5 (V/Hz^0.5)
Vg-Vth or ID/gm(V) Vg-Vth
ID/gm
PMOS WL=10um/1um
Two Curve use Same Svg Data Fit
Fig8 The contours of stress distribution across the whole device.
Fig.9 The stress distribution along the channel width.
-6 -4 -2 0 2 4 6
0 200 400 600 800 1000
Stress (MPa)
Width Dirction (um)
W=10um W=1um W=0.6um W=0.24um W=0.11um
Fig.10 Comparing our simulation result with Shih[18].
0.1 1 10
0 100 200 300 400 500 600
Stress silution(MPa)
Channel width(um) Our Simulaiton Simulation by Shih
Fig11 The separated stress in terms of the average edge stress and average flat region stress.
0.1 1 10
0 200 400 600 800
Stress (Mpa)
Channel width (um) Flat Stress Simulation Edge Stress Simulation
Table1The Measured long p- and n-channel MOSFET piezoresistance coefficients for (001) and (110) wafers compared to bulk Si
piezoresistance [15]
Fig.12 The Vth shfit due to gate to STI spacing (A) induced stress.
0.1 1 10
-0.28 -0.27 -0.26 -0.25 -0.24 -0.23
Vth(V)
Gate to STI Spacing (um)
Fig.13 The mobility shift due to gate to STI spacing (A) induced stress.
-1.1 -1.0 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 20
30 40 50 60 70
Mobility (cm^2/V-s)
Vg(V) A=0.21um A=0.495um A=2.4um A=10um
Fig .14 measured Svg0.5 varies Id/g at 25Hz with spacing A=10um.
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
0.000000 0.000002 0.000004 0.000006 0.000008
SVg^0.5 (V/Hz^0.5)
ID/gm(V) PMOS WL=10um/1um Gate to STI Spacing A=10um
Fig .15 measured Svg0.5 varies Id/g at 25Hz with spacing A=2.4um
0.0 0.1 0.2 0.3 0.4 0.5 0.6
0.000000 0.000002 0.000004 0.000006 0.000008
PMOS WL=10um/1um Gate to STI Spacing A=2.4um
SVg^0.5 (V/Hz^0.5)
ID/gm(V)
Fig .16 measured Svg0.5 varies Id/g at 25Hz with spacing A=0.495um
0.0 0.1 0.2 0.3 0.4 0.5 0.6
0.000000 0.000002 0.000004 0.000006
PMOS WL=10um/1um
Gate to STI Spacing A=0.495um
SVg^0.5 (V/Hz^0.5)
ID/gm
Fig .17 measured Svg0.5 varies Id/g at 25Hz with spacing A=0.21um.
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
0.000001 0.000002 0.000003 0.000004 0.000005 0.000006
0.000007 PMOS WL=10um/1um Gate to STI Spacing A=0.21um
SVG^0.5(V/Hz^0.5)
ID/gm(V)
Fig.18 The fittings used line for extracting the trap density Nt (cm-3eV-1) and scattering factor α (Vs/C)
0.0 0.1 0.2 0.3 0.4 0.5 0.6
0.000001 0.000002 0.000003 0.000004 0.000005 0.000006
Svg^0.5(V/Hz^0.5)
ID/gm(V) A=10um
A=2.4um A=0.495um A=0.21um
Fig.19(a) The trap density Nt(cm-3eV-1). (b) the scattering factor α variation. Varies gate to STI Spacing
1 10
1E18 2E18 3E18 4E18 5E18
Nt (cm-3 eV-1)
Gate to STI Spacing A(um)
0.1 1 10
2.0x104 4.0x104 6.0x104 8.0x104 1.0x105 1.2x105 1.4x105 1.6x105 1.8x105
Scattering Factor (Vs/C)
Gate to STI Spacing (um)
Fig.22(a)
Fig.22(b)
Fig 20 The Vth shift in narrow device, at L=1um,W=10,1,0.6,0.24, and 0.11um,
0.1 1 10
-0.26 -0.24
Vth (V)
Channel WIdth (um) PMOS Comapressive STI
Fig.21a The mobility varies gate voltage of five device (W=10,1,0.6,0.24,0,11um), L=1um.
0.1 1 10
PMOS Compressive L=1um At Vd=-0.5V
Predict Compressive Stress Mobility Change
-1.0 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2
Moblility (cm^2/ V-s)
Vg(V)
Fig 22a measured Svg0.5 varies Id/gm at 25Hz with W=10um.
Fig 22b The fitting line at 25Hz with W=10um
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Extraction frequency @ 25Hz
0 .0 0 .1 0 .2 0 .3 0 .4 0.5 0 .6 Average S vg^0.5 V s ID/gm
Fig 23a measured Svg0.5 varies Id/gm line at 25Hz with W=1um.
Fig 23b The fitting line at 25Hz with W=1um.
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Average SVg Vs ID/gm
Fig 24a measured Svg0.5 varies Id/gm at 25Hz with W=0.6um
Fig 24b The fitting line at 25Hz with W=0.6um
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Average SVg Vs ID/Gm
Fig 25a measured Svg0.5 varies Id/gm line at 25Hz with W=0.24um
Fig 25b The fitting line at 25Hz with W=0.24um
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Extraction Frequency @ 25Hz
0.0 0.1 0.2 0.3 0.4 0.5 0.6 Average SVG Vs ID/gm
Fig. 26a measured Svg0.5 varies Id/gm at 25Hz with W=0.11um
Fig. 26b The fitting line at 25Hz with W=0.11um
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Average SVg VS ID/Gm
Fig.27a The Trap density Nt variation in narrowing devices.
Fig.27b The scattering factor α variation in narrowing devices.
0.1 1 10
1E17 1E18
NT (cm-3 eV-1)
Channel Width(um)
0.1 1 10
5.0x104 1.0x105 1.5x105 2.0x105 2.5x105 3.0x105
Scattering Factor (Vs/C)
Channel WIdth (um)