MIT-IC lab testing

Polysilicon

Fall 2005 – M.A. Schmidt
Single Crystal Silicon
Figure removed for copyright reasons.
Please see: Figure 3-5 in Pierret, Robert, and Gerold Neudeck. Modular Series on Solid State Devices. Reading, MA: Addison-Wesley, 1982. ISBN: 0201052873.
Please see: Kamins, T. Polysilicon for Integrated Circuit Application. Norwell, MA: Kluwer Academic Publishers, 1988.
T. Kamins Kluwer
Fall 2005 – M.A. Schmidt 3.155J/6.152J – Lecture 5 – Slide 16
MOS Capacitor
t
A
C = ε A/t = εrεo A/t C* = C / A εr (SiO2) = 3.9
Fall 2005 – M.A. Schmidt
εo = 8.85 x 10-14 F/cm
3.155J/6.152J – Lecture 5 – Slide 17
MOS Capacitance Measurement
RS = 4.53 Rave Rave = ½ (R’+R’’)
Fall 2005 – M.A. Schmidt
3.155J/6.152J – Lecture 5 – Slide 9
N Square Resistor
L = Lmask + ∆L
W = Wmask + ∆W
N = Lmask/Wmask >>1
Fall 2005 – M.A. Schmidt 3.155J/6.152J – Lecture 5 – Slide 25
MOS Capacitance Measurement
Three measurements Cox Cmin VFB Produce tox ND Qf CFB
Fall 2005 – M.A. Schmidt
R. Pierret
Fall 2005 – M.A. Schmidt 3.155J/6.152J – Lecture 5 – Slide 13
Single Crystal Silicon
Figure removed for copyright reasons.
Please see: Plummer, J., M. Deal, and P. Griffin. Silicon VLSI Technology: Fundamentals, Practice, and Modeling. Upper Saddle River, NJ: Prentice Hall, 2000. ISBN: 0130850373.
L = W
R = RS
Fall 2005 – M.A. Schmidt 3.155J/6.152J – Lecture 5 – Slide 5
Number of Squares
R = 2RS
R = RS/2
R = RS/3
R = 8RS
Fall 2005 – M.A. Schmidt
R = 6.5RS
T. Kamins Kluwer
Fall 2005 – M.A. Schmidt 3.155J/6.152J – Lecture 5 – Slide 15
Polysilicon Resistivity vs Dopant
Use for lab report
Figure removed for copyright reasons.
Resistivity Ω-cm
Fall 2005 – M.A. Schmidt
Process
Mask
3.155J/6.152J – Lecture 5 – Slide 4
Concept of Sheet Resistivity
R = ρ L/A = (ρ/t) (L/W)
Sheet Resistivity (RS) Ω/sq # of Squares
I I
+
V
-
Eliminates the effect of contact resistance
Fall 2005 – M.A. Schmidt
3.155J/6.152J – Lecture 5 – Slide 11
Analysis of Resistivity

Semiconductor Resistivity(ρ)/Conductivity(σ)
Plummer
Fall 2005 – M.A. Schmidt 3.155J/6.152J – Lecture 5 – Slide 14
Poly Resistivity vs Dep. Temp.
re removed for copyright reasons.
Please see: Kamins, T. Polysilicon for Integrated Circuit Application. Norwell, MA: Kluwer Academic Publishers, 1988.
Oxide
n-Si
C* = C / A
Fall 2005 – M.A. Schmidt 3.155J/6.152J – Lecture 5 – Slide 19
MOS Capacitor in Accumulation
+ + + + + + + +
-
C* = Cox = εox / tox
Fall 2005 – M.A. Schmidt 3.155J/6.152J – Lecture 5 – Slide 20
0.2 1
Fall 2005 – M.A. Schmidt
10
100
1000
R’/R’’
3.155J/6.152J – Lecture 5 – Slide 8
Van der Pauw

Implement a symmetric structure

R’ = R’’ f(R’/R’’) = 1


1/ρ = σ = q(µnn + µpp) n >> p σ = qµnn n=N (doping density) µSi = f(N) µpoly << µSi
3.155J/6.152J – Lecture 5 – Slide 12

N-type


Single Crystal Silicon
Fall 2005 – M.A. Schmidt
3.155J/6.152J – Lecture 5 – Slide 24
Effect of Oxide Charge
+ + + + + + + +
+ + + +
- - - - -
A net shift in C-V curve:
Need to add more negative charge (voltage) to invert surface
+ -
VGB vac
iac Ref: A. Akinwande
Fall 2005 – M.A. Schmidt
3.155J/6.152J – Lecture 5 – Slide 18
MOS Capacitor
Poly
tox
+ - + - + - + - + - + - + - + + - + - + - + - + - + - + - + + - + - + - + - + - + - + - + + - + - + - + + - + - + - + - + - + - + + - + - + - + - + - + - + + - + - + - + - + - + - + + - + - + - +
xs xs,max
Rapid VGB Change
Flatband VGB
VT Inversion
VFB
Depletion Accumulation
Cs = εSi / xs
Fall 2005 – M.A. Schmidt 3.155J/6.152J – Lecture 5 – Slide 23
C-V
R = RS (L/W) = RS [Lmask/(Wmask +∆W)]
Used to determine the process ‘bias’ (∆W)
Fall 2005 – M.A. Schmidt 3.155J/6.152J – Lecture 5 – Slide 10
4-Point Probe
3.155J/6.152J Lecture 5:
IC Lab Testing