detailed placement for improved depth of focus and cd control
DESCRIPTION
Detailed Placement for Improved Depth of Focus and CD Control. Puneet Gupta 1 ([email protected]) Andrew B. Kahng 1,2 Chul-Hong Park 2. 1 Blaze DFM, Inc. 2 ECE Department, University of California, San Diego. Outline. OPC and SRAF: An Introduction The AFCorr Methodology - PowerPoint PPT PresentationTRANSCRIPT
Detailed Placement for Detailed Placement for Improved Depth of Focus and Improved Depth of Focus and
CD ControlCD Control
Puneet GuptaPuneet Gupta11
([email protected])([email protected])
Andrew B. KahngAndrew B. Kahng1,21,2
Chul-Hong ParkChul-Hong Park22 1 Blaze DFM, Inc.
2 ECE Department, University of California, San Diego
OutlineOutline
OPC and SRAF: An IntroductionOPC and SRAF: An Introduction The AFCorr MethodologyThe AFCorr Methodology AFCorr Placement PerturbationAFCorr Placement Perturbation Experiments and ResultsExperiments and Results SummarySummary
OPC (Optical Proximity Correction)OPC (Optical Proximity Correction)
Gate CD control is extremely difficult to achieveGate CD control is extremely difficult to achieve Min feature size outpaces introduction of new hardware solutionsMin feature size outpaces introduction of new hardware solutions
OPC = one of available reticle enhancement techniques OPC = one of available reticle enhancement techniques (RET) to improve pattern resolution(RET) to improve pattern resolution Proactive distortion of photomask shape Proactive distortion of photomask shape compensate CD compensate CD
inaccuraciesinaccuracies
Before OPC After OPCC.-H. Park et al., SPIE 2000
SRAF (Sub-Resolution AF)SRAF (Sub-Resolution AF)
SRAF = Scattering Bar (SB)SRAF = Scattering Bar (SB) SRAFs enhance process window (focus, exposure dose) SRAFs enhance process window (focus, exposure dose)
Extremely narrow lines Extremely narrow lines do not print on water do not print on water More SBs helps to enhance DOF margin and to meet the target CDMore SBs helps to enhance DOF margin and to meet the target CD
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
0.22
0.0 0.1 0.2 0.3 0.4 0.5 0.6
SB2 SB1 SB0
DOF
CD
SB=0
SB=2SB=1
Active
#SB = 0 #SB=1 #SB=2160 177 182CD (nm)
Layout (or Mask ) Design Process Margin (180nm)
Wafer structure (SEM)
SRAFs and Bossung PlotsSRAFs and Bossung Plots
Bossung plotBossung plot Measurement to evaluate lithographic manufacturability Measurement to evaluate lithographic manufacturability Maximize the common process windowMaximize the common process window Horizontal axis: Depth of Focus (DOF); Vertical axis: CDHorizontal axis: Depth of Focus (DOF); Vertical axis: CD
SRAF OPC SRAF OPC Improves process margin of isolated pattern Improves process margin of isolated pattern Larger overlap of process window between dense and isolated linesLarger overlap of process window between dense and isolated lines
-20
20
60
100
140
180
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
DOF (um)
CD
(n
m)
12
11.5
11
10.5
10
9.5
Bias OPC SRAF OPC
-20
20
60
100
140
180
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
DOF (um)
CD
(n
m)
12
11.5
11
10.5
10
9.5
OutlineOutline
OPC and SRAF: An IntroductionOPC and SRAF: An Introduction The AFCorr MethodologyThe AFCorr Methodology AFCorr Placement PerturbationAFCorr Placement Perturbation Experiments and ResultsExperiments and Results SummarySummary
Forbidden PitchesForbidden Pitches
Forbidden pitch lowers printability, DOF margin Forbidden pitch lowers printability, DOF margin and exposure marginand exposure margin
Typically based on tolerance of +/- 10% of CD Must avoid forbidden pitches in layout
-30
10
50
90
130
170
100 300 500 700 900 1100 1300 1500
pitch (nm)
CD
(n
m)
W/O OPC(Best DOF)W/O OPC(Defocus)
Bias OPC(Defocus)SRAF OPC (Defocus)
#SB=1 #SB=2 #SB=3 #SB=4
Allowable
Forbidden
Layout Composability for SRAFsLayout Composability for SRAFs
Small set of allowed feature spacingsSmall set of allowed feature spacings Two components of SRAF-aware methodologyTwo components of SRAF-aware methodology
Assist-correct librariesAssist-correct libraries Library cell layout should avoid all forbidden pitchesLibrary cell layout should avoid all forbidden pitches Intelligent library designIntelligent library design
Assist-correct placement Assist-correct placement THIS WORK THIS WORK Intelligent whitespace adjustment in the placerIntelligent whitespace adjustment in the placer
x+x x
Better than
OutlineOutline
OPC and SRAF: An IntroductionOPC and SRAF: An Introduction The AFCorr MethodologyThe AFCorr Methodology AFCorr Placement PerturbationAFCorr Placement Perturbation Experiments and ResultsExperiments and Results SummarySummary
AFCorrAFCorr: SRAF-Correct Placement: SRAF-Correct Placement
By adjusting whitespace, additional SRAFs can be inserted between cells Resist image improves after assist-aware placement
adjustment Problem: Perturb given placement minimally to
achieve as much SRAF insertion as possible
Cell boundaryForbidden pitch
Before AFCorr After AFCorr
Minimum Perturbation ApproachMinimum Perturbation Approach
Objective:Objective: Reduce forbidden pitch violationReduce forbidden pitch violation Reduce weighted CD degradation with defocusReduce weighted CD degradation with defocus Minimum perturbation: preserve timingMinimum perturbation: preserve timing
Constraint:Constraint: Placement site width must be respectedPlacement site width must be respected
How:How: One standard cell row at a timeOne standard cell row at a time Solve each cell row by Solve each cell row by dynamic programmingdynamic programming
Feasible Placement PerturbationsFeasible Placement Perturbations
Minimize Minimize i i ||
s.t. s.t. a-1a-1a a ++SSa-1a-1RP RP + S+ Saa
LPLP + (x + (xaa – x – xa-1a-1 – w – wa-1a-1) ) AF AFwi and xi = width and location of Ci
i = perturbation of location of cell Ci
AF = set of allowed spacingsRP, LP = boundary poly shapes with overlapping y-spans
- Overlap types: g-g, g-f, f-f
S = spacing from boundary poly to cell border
xxaaxxa-1a-1
SSa-1a-1RPRP
SSaaLPLP
WWa-1a-1
gategate
field
field
Vertical Forbidden PitchesVertical Forbidden Pitches
Handled in a way similar to horizontal overlapHandled in a way similar to horizontal overlap Usually field polyUsually field poly Typically, #vertical forbidden pitches < #horiz. F.P.Typically, #vertical forbidden pitches < #horiz. F.P.
Due to restricted design rules like single orientation polyDue to restricted design rules like single orientation poly
Row i-1
Row i
Cell under consideration
Dynamic Programming SolutionDynamic Programming Solution
perturbationweight αα, , ββ = weights for horizontal vs vertical forbidden pitches = weights for horizontal vs vertical forbidden pitches Slope = Slope = CD / CD / Pitch = CD degradation per unit space between AF values Pitch = CD degradation per unit space between AF values AFAFii = closest assist-feasible spacing ≤ HSpace = closest assist-feasible spacing ≤ HSpace Overlap_weight = overlap length weighted by relative importance of printability Overlap_weight = overlap length weighted by relative importance of printability
for gate-to-gate, gate-to-field, and field-to-fieldfor gate-to-gate, gate-to-field, and field-to-field
COST (1,b) = | xCOST (1,b) = | x11-b| -b| // subrow up through cell 1, location b// subrow up through cell 1, location bCOST (a,b) = COST (a,b) = (a) |(x(a) |(xaa -b)| + -b)| +
MINMIN{X{Xaa-SRCH ≤ i ≤ X-SRCH ≤ i ≤ Xaa+SRCH}+SRCH} [COST(x [COST(xa-1a-1,i) + ,i) + ααHCost(a,b,a-1,i) HCost(a,b,a-1,i)
+ + ββVCost(a,b)]VCost(a,b)] // SRCH = maximum allowed perturbation of cell location// SRCH = maximum allowed perturbation of cell location
HCost = horizontal “forbidden-pitch cost” = sum over horiz-HCost = horizontal “forbidden-pitch cost” = sum over horiz- adjacencies of adjacencies of
[slope(j) |HSpace –AF[slope(j) |HSpace –AF jj| * overlap_weight]| * overlap_weight] s.t. AFs.t. AFj+1j+1 > HSpace > HSpace AF AFj j
VCost = vertical forbidden pitch costVCost = vertical forbidden pitch cost
OutlineOutline
OPC and SRAF: An IntroductionOPC and SRAF: An Introduction The AFCorr MethodologyThe AFCorr Methodology AFCorr Placement PerturbationAFCorr Placement Perturbation Experiments and ResultsExperiments and Results SummarySummary
Experimental FlowExperimental Flow
Forbidden pitch
SB OPC
- SB Insertion- Model-based OPC (Best DOF model)
Lithography modelgeneration
(Best & Worst DOF)
Benchmark design
Placement
Assist CorrectedGDS
Route
Typical GDS
Route
Post-Placement
OPCed GDSs
- Delay - GDSII size- OPC Run Time- # Forbidden pitch- # SB - # EPE
Experiments
Experimental SetupExperimental Setup KLA-Tencor’s KLA-Tencor’s ProlithProlith
Model generation for Model generation for OPCproOPCpro Best focus/ worst (0.5 micron) defocusBest focus/ worst (0.5 micron) defocus
Calculating forbidden pitchesCalculating forbidden pitches Mentor’s Mentor’s OPCproOPCpro, SBar , SBar SVRFSVRF
OPC, SRAF insertion, ORC (Optical Rule Check)OPC, SRAF insertion, ORC (Optical Rule Check) Cadence Cadence SOC EncounterSOC Encounter
Placement & RoutePlacement & Route Synopsys Design ComplierSynopsys Design Complier
SynthesisSynthesis
Experimental MetricsExperimental Metrics SB Count
Total number of scattering bars or SRAFs inserted in the design
Higher number of SRAFs indicates less through-focus variation and is hence desirable
Forbidden Pitch Count Number of border poly geometries estimated as
having greater than 10% CD error through-focus EPE Count
Number of edge fragments on border poly geometries having greater than 10% edge placement error at the worst defocus level
Results: Increased SB CountResults: Increased SB Count
SB count increases as utilization decreases due to increased whitespace
#SB increases after AFCorr placement
0
50000
100000
150000
200000
250000
300000
90 80 70 60 50
Utilization(%)
# T
ota
l SB
0
10000
20000
30000
40000
50000
60000
70000
80000
90000
# S
B D
iffe
ren
ce
SB difference (130)SB difference (90)SB w/o AFCorr(130)SB w AFCorr(130)SB w/o AFCorr(90)SB w AFCorr(90)
Results: Reduced F/P and EPEResults: Reduced F/P and EPE
Forbidden pitch count (border poly only) 81%~100% in 130nm, 93%~100% in 90nm
EPE Count (border poly only) 74%~95% in 130nm, 83%~96% in 90nm
60
70
80
90
100
90 80 70 60 50
Utilization(%)
Red
uct
ion
(%
)
EPE (130)
EPE (90)F/Pitch (130)
F/Pitch (90)
Impact on Other Design MetricsImpact on Other Design Metrics
Impact : Data size < 1%, OPC run time < 2%, Cycle time < Impact : Data size < 1%, OPC run time < 2%, Cycle time < 4%4%
Other impacts are negligible compared to large improvement Other impacts are negligible compared to large improvement in printability metricsin printability metrics
Utilization(%)Utilization(%) 9090 8080 7070
Flow:Flow: OrigOrig AFCorrAFCorr OrigOrig AFCorrAFCorr OrigOrig AFCorrAFCorr
130nm130nm #EPE#EPE 48904890 47214721 59755975 562562 42764276 1515
R/T (s)R/T (s) 78217821 79027902 78767876 79347934 79137913 79737973
GDS (MB)GDS (MB) 48.948.9 48.948.9 48.848.8 48.948.9 48.248.2 48.448.4
Delay (ns)Delay (ns) 4.24.2 4.64.6 4.54.5 4.74.7 4.54.5 4.64.6
90nm90nm #EPE#EPE 75237523 12621262 48134813 532532 21312131 107107
R/T(s)R/T(s) 62116211 63276327 63226322 64316431 64826482 64996499
GDS(MB)GDS(MB) 43.143.1 43.343.3 43.243.2 43.343.3 43.243.2 43.343.3
Delay(s)Delay(s) 2.72.7 2.72.7 2.62.6 2.62.6 2.42.4 2.52.5
OutlineOutline
OPC and SRAF: An IntroductionOPC and SRAF: An Introduction Forbidden Pitch Extraction Forbidden Pitch Extraction The AFCorr MethodologyThe AFCorr Methodology Experiments and ResultsExperiments and Results SummarySummary
SummarySummary AFCorr is an effective approach to achieve
assist feature compatibility in physical layout Up to 100% reduction of forbidden pitch and Up to 100% reduction of forbidden pitch and
EPEEPE Relatively negligible impacts on GDSII size, Relatively negligible impacts on GDSII size,
OPC runtime, and design clock cycle timeOPC runtime, and design clock cycle time Compared to huge improvement in printabilityCompared to huge improvement in printability
Ongoing researchOngoing research Developing “correct-by-construction" standard-cell
layouts which are always AFCorrect in any placement
Thank You!
NotationNotation
W = cell width; W = cell width; RP, LP = Boundary poly geometriesRP, LP = Boundary poly geometries S = Spacing from boundary poly to cell borderS = Spacing from boundary poly to cell border O = Parallel adjacencies between poly features (g-f, g-g, f-f)O = Parallel adjacencies between poly features (g-f, g-g, f-f) Example:Example: S Sa-1a-1
RP2 RP2 + (x+ (xa-1a-1 – x – xaa – w – wa-1a-1) + S) + SaaLP3LP3 should be assist-correct should be assist-correct
A