“LAYOUT” EFFECTS
HOW LAYOUTS CAN CHANGE CMOS
AND HOW DO CIRCUIT SIMULATIONS
ACCOUNT FOR THE CHANGE
BOB PEDDENPOHL
MODELING MANAGER
CYPRESS MODELING CENTER
LEXINGTON, KY
04/04/07
AGENDA (ACRONYM TEST)
BSIM BASICS, NEW FEATURES
BERKLEY SHORT CHANNEL IGFET MODEL
STI EFFECT OR LOD EFFECT
SHALLOW TRENCH ISOLATION OR LENGTH OF DIFFUSION
WPE
WELL PROXIMITY EFFECTS
OPC
OPTICAL PROXIMITY CORRECTION
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AGENDA
BSIM BASICS, NEW FEATURES
LENGTH-OF-DIFFUSION (LOD)
WELL PROXIMITY EFFECTS (WPE)
OPTICAL PROXIMITY CORRECTION (OPC)
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BSIM BASICS
SPICE SIMULATION OF MOS (ONLY APPROXIMATIONS!)
HAND CALC: Ids = width/length * Cox * Mobility * (Vgs – Vth - Vdsat) * Vds
SPICE CALC: Ids = w/l * 1/TOX * U0 * (Vgs – VTH0 – VDSAT) * Vds
TERMINOLOGY
SPICE MODEL PARAMETERS (BSIM3 PARAMETERS)
INSTANCE PARAMETERS
SIMULATION PARAMETERS (BIAS CONDITIONS)
MODEL EXAMPLE:
.model nshort.1 nmos
TOX = 4.19e-9
NETLIST EXAMPLE:
m1 d g s b nshort w =25 l=0.5 m=1 ad=50 pd=27..delvth0=0.0 sa=1.04 sb=1.04
v1 g s 1.8
v2 d s 0.9
v3 b s 0.0
COMMAND RUN EXAMPLE
spectre mynetlist.scs
WAVEFORM VIEWER TO REVIEW SPECTRE OUTPUT FILES
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BSIM3 VS BSIM4
WHAT ARE UPGRADES IN BSIM4?
LOD
WPE
RF MODELING IMPROVEMENTS
BSIM: http://www-device.eecs.berkeley.edu/~bsim3/
BSIM = BERKELEY SHORT-CHANNEL IGFET MODEL
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MODEL DEVELOPMENT PROCESS
SELECT “GOLDEN” WAFER
MEASUREMENT (DC, AC, TRAN)
EXTRACT WAFER CASE MODEL
RO MEAS = RO SIMS
CENTER TO EDR NOMINAL (TT)
SKEW MODELS (FF, SS, FS, SF)
QA & RELEASE TO DESIGN
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AGENDA
BSIM BASICS, NEW FEATURES
LENGTH-OF-DIFFUSION (LOD)
WELL PROXIMITY EFFECTS (WPE)
OPTICAL PROXIMITY CORRECTION (OPC)
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LAYOUT CHOICES & LOD

BEST VALUE FOR Sa, Sb? WHY BIGGER DIFFUSIONS?
Sa
Sb
Sa
Sb
Sa
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Sb
MEASURED DATA

VTH DUE TO STI STRESS
Sa, Sb Instance
params for LOD
Sa
Sb
Sa
Sb
Nmos VTH Variation Optical Effect and STI Effect
0.70
0.69
STI Effect
VTH
0.68
0.67
Site1
0.66
Site2
0.65
Site4
0.64
Proximity Effect
0.63
0.62
Width=7
P ro xB ars# 2
LOD=1.04
9
Width=7
P ro xB ars# 1
LOD=1.04
Width=7
P ro xB ars# 0
LOD=1.04
Width=7
P ro xB ars# 0
LOD=0.925
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Width=7
P ro xB ars# 0
LOD=0.68
Width=7
P ro xB ars# 0
LOD=0.28
LOD MODEL EQUATIONS
Sa
ELECTRICAL
PARAM
SPICE/MODEL EQN
(APPROX)
MODEL FITTING
CURVE
Vth
VTH0 + KVTH0
Vth vs Sa, Sb
Vth w/ Vbs
Vth + K2 + STK2
Vth@Vbs vs Sa, Sb
Ids_linear
(Ids vs Vds)
Mobility = U0 + KU0
Idslin vs Sa, Sb
Ids_sat
Vsat = VSAT + KVSAT
Ids vs Sa,Sb
Rout (Output
Resistance)
Rout = 1/Gds + STETA0
Rout vs Sa,Sb
STRESS MODEL PARAMETERS f(Sa,Sb)
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Sb
SPICE WITH LOD EFFECTS

BEST VALUE FOR Sa, Sb? WHY?
Sa
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Sb
Sa
Sb

NETLIST WITH LOD
m1 d g s b nshort w =25 l=0.5 m=1 ad=50 pd=27..delvth0=0.0 sa=1.04 sb=1.04

IDS SPICE APPROX WITH LOD
SPICE CALC: Ids = w/l * 1/TOX * (U0 + KU0) * (Vgs – VTH0 – VDSAT) * Vds

ALTERNATIVES TO MODELING?
 MODEL  INSTANCE PARAMETERS + MODEL PARAMETERS
 DRC  ENFORCE SINGLE SA, SB VALUE ALLOWED
 CORNER MODELS  PUT WIDER VARIATION INTO MODEL

ADVANTAGES/DISADVANTAGES?
 SIMULATION TIME & ACCURACY, MODEL DEVELOPMENT TIME
 SILICON AREA INCREASES
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AGENDA
BSIM BASICS, NEW FEATURES
LENGTH-OF-DIFFUSION (LOD)
WELL PROXIMITY EFFECTS (WPE)
OPTICAL PROXIMITY CORRECTION (OPC)
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WPE BACKGROUND
0.74
nwell
0.73
Vth
0.72
Wspc
0.71
0.7
0.69
Wspc
0.68
0.67
0
2
4
6
Wspc
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
WHAT’S THE CAUSE?

http://www.ieee-cicc.org/06-8-6.pdf
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RECALL PROCESSING STEPS
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NWELL IMPLANT EFFECTS CMOS
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
HIGH ENERGY ATOMS BOUNCE OFF PHOTORESIST

http://www.ieee-cicc.org/06-8-6.pdf (see paper diagrams)

WHY WPE NOW?

SPICE MODEL OF WPE

REFERENCE:
 HIGH ENERGY IMPLANTERS
 WANT DEEP IMPLANT  LOW RES PATH  SUPRESS BJT LATCHUP
 Vth = VTH0 + KVTHOWE*(sca+WEB*scb + WEC*scc)
 Vth@Vbs = K2 + K2WE * (sca + WEB*scb +WEC*scc)
 Mobility = U0 * (1+KU0WE*(sca + WEB*scb+WEC*scc)
 COMPACT MODEL COUNCIL WEBSITE
 BSIM4 MANUAL FROM BERKELEY WEBSITE
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SPICE WITH WPE EFFECTS nwell

INSTANCE PARAMS ALL FUNCTION Wspc
 Sca, scb, scc
Wspc
ELECTRICAL
PARAM
SPICE/MODEL EQN (APPROX)
MODEL FITTING
CURVE
Vth
VTH0 + KVTHOWE*(sca+WEB*scb + WEC*scc)
Vth vs sca,scb,scc
Vth w/ Vbs
Vth + K2 + K2WE * (sca + WEB*scb +WEC*scc)
Vth@Vbs vs sca,scb,scc
Mobility
U0 * (1+KU0WE*(sca+WEB*scb+WEC*scc)
IDS Lin vs sca,scb,scc

NETLIST WITH WPE
m1 d g s b nshort w =25 l=0.5 m=1 ad=50 pd=27..delvth0=0.0 sca=1.1 scb=0.5, scc=3
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
IDS SPICE APPROX WITH WPE

ADVANTAGES/DISADVANTAGES/ALTERNATIVES?
SPICE: Ids = w/l * 1/TOX * (U0 + f(KU0WE) * (Vgs – VTHO + f(KVTHOWE) – Vdsat) * Vds
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AGENDA
BSIM BASICS, NEW FEATURES
LENGTH-OF-DIFFUSION (LOD)
WELL PROXIMITY EFFECTS (WPE)
OPTICAL PROXIMITY CORRECTION (OPC)
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RF FET Modules Layout
With poly proximity bars
M=2
M=4
Standard Layout
Without poly
proximity bars
Is performance the same?
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OPC BACKGROUND
OPTICAL PROXIMITY CORRECTION (OPC)
DURING LIGHT EXPOSING OF PHOTORESIST FINAL SHAPES ON SILICON NOT
MATCH DRAWN SHAPES
BASED ON SURROUNDING ENVIRONMENT
With proximity bars
Standard Layout
Without proximity
bars
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MEASURED DATA

VTH DUE TO STI STRESS
Sa, Sb Instance
params for LOD
Sa
Sb
Sa
Sb
Nmos VTH Variation Optical Effect and STI Effect
0.70
0.69
STI Effect
VTH
0.68
0.67
Site1
0.66
Site2
0.65
Site4
0.64
Proximity Effect
0.63
0.62
Width=7
P ro xB ars# 2
LOD=1.04
20
Width=7
P ro xB ars# 1
LOD=1.04
Width=7
P ro xB ars# 0
LOD=1.04
Width=7
P ro xB ars# 0
LOD=0.925
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Width=7
P ro xB ars# 0
LOD=0.68
Width=7
P ro xB ars# 0
LOD=0.28
MEASURED DATA

VTH DUE TO PROXIMITY AND STI STRESS
Nmos VTH Variation Optical Effect and STI Effect
0.70
0.69
STI Effect
VTH
0.68
0.67
Site1
0.66
Site2
0.65
Site4
Proximity Effect
0.64
0.63
0.62
Width=7
P ro xB ars# 2
LOD=1.04
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Width=7
P ro xB ars# 1
LOD=1.04
Width=7
P ro xB ars# 0
LOD=1.04
Width=7
P ro xB ars# 0
LOD=0.925
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Width=7
P ro xB ars# 0
LOD=0.68
Width=7
P ro xB ars# 0
LOD=0.28
DRAWN NOT EQUAL FINAL
OPC “SIMULATION” TOOL  IN: LAYOUT, OUT: POLY SHAPES
Lcenter
Ledge
Ltrans
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W/L/M
Lcenter
Ledge
Ltrans
3/0.15/2
0.15
0.214
0.17
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M=2 AND M=4 COMPARISON
W/L/M
Lcenter
Ledge
Ltrans
3/0.15/2
0.15
0.214
0.17
3/0.15/4
(edge)
0.15
0.204
0.185
3/0.15/4
(center)
0.15
0.234
0.185

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SAME DRAWN L, BUT SILICON
VARIES
DESIGNING WITH OPC
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
NO SPICE MODEL EFFECT

RELY ON CLDRC, NOT PERFECT

ACCOUNT FOR IN YOUR DESIGN?
 L(DRAWN) = L(SI)
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MEASURED DATA

VTH DUE TO PROXIMITY AND STI STRESS
Sa
Sb
Sa
Sb
Nmos VTH Variation Optical Effect and STI Effect
0.70
0.69
STI Effect
VTH
0.68
0.67
Site1
0.66
Site2
0.65
Site4
Proximity Effect
0.64
0.63
0.62
Width=7
P ro xB ars# 2
LOD=1.04
25
Width=7
P ro xB ars# 1
LOD=1.04
Width=7
P ro xB ars# 0
LOD=1.04
Width=7
P ro xB ars# 0
LOD=0.925
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Width=7
P ro xB ars# 0
LOD=0.68
Width=7
P ro xB ars# 0
LOD=0.28
CONCLUSIONS

LOD/WPE IMPACT TRANSISTOR PERFORMANCE, ACCOUNT FOR BY:

NEW PHYSICAL EFFECTS RELY HEAVILY ON INSTANCE PARAMETERS OR
CLDRC
 MODEL  ACCURATE AT COST OF MODEL DEVELOPMENT
 DRC RULES  EASIER DESIGN KIT AT COST OF AREA
 INTERACTION OF THE MODEL WITH CAD TOOLS

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GOOD DESIGNER:
 LIMIT THESE EFFECTS AS MUCH AS POSSIBLE IN LAYOUT
 REVIEW MODELS TO ENSURE EFFECTS ARE INCLUDED
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APPENDIX
EXECUTIVE SUMMARY

PROBLEM STATEMENT
 TRANSISTOR PARAMETRIC SHIFTS DUE TO PROXIMITY EFFECTS
 PHOTO/ETCH: DENSE VS ISOLATED
 STI STRESS: POLY-STI EDGE SPACING

WHAT WAS DONE
 ELECT/OPTICAL CHAR OF DENSE VS ISOLATED ON L8
 PHOTO/ETCH VS STI STRESS CHAR ON S8

WHAT NEEDS TO BE DONE (TO BE FORMALIZED)
WHAT
LIST OF TEST STRUCTURES TO QUANTIFY IMPACT
TEST STRUCTURES MODELING TEST STRUCTURES
PLACEMENT ON L8/S8 FRAMES
WHO
SBJ
PED
JFE
OPC METHODOLOGY FOR ISO/DENSE CONSISTENCY FNG
TECHNOLOGY
MODELING
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TECHNIQUES FOR STRESS RELIEF
TDR RULES FOR MIN LOD, FIXED LAYOUT
METHODOLOGY UPDATE FOR STRESS PARAMETER
EXTRACTION IN BSIM4
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HRP
PED
MEASUREMENTS: COMPLETE MOS




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FET DC (VTH0, RDSW)
FET AC (CGDO,DLC)
DIODE DC (JS,JSW)
DIODE AC (CJ, CJSW)
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Stress Equations in Model
 Measurements done by SBJ
 As NMOS gets closer to STI Edge, VT Increases, IDS
and Gm Decrease
 As PMOS gets closer to STI Edge, |VT| Decreases,
IDS and Gm Increase.
 STI induced Stress degrades NMOS and enhances
PMOS characteristics (why enhanced?)
 More measurements are planned.
 Data is plotted for # of proximity bars and length of
diffusion (LOD).
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W=3.01 L=0.15 M2
 L = 0.158-0.008=0.15um at center
 L=0.222-0.008 = 0.214um at edge
 Transition region from edge before L
becomes 0.15um  0.17um
 Impact will be larger for W=1.65
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W=3.01 L=0.15 M4
 L = 0.158-0.008=0.15um at center
 L=0.232-0.008 = 0.234um at edge of
center two fingers
 L=0.212-0.008 = 0.204um at edge of
outer fingers
 Transition region from edge before L
becomes 0.15-0.155um = 0.185um
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