spie (2005) vol. 5755_16 tea systems, inc. terrence e. zavecz – tea systems inc. march 3, 2005...
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SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
Terrence E. Zavecz – TEA Systems Inc.http://www.TEAsystems.com
March 3, 2005
Full-Field feature profile models in process control
Contact [email protected]
(+01) 610 682 4146
SPIE (2005) Vol 5755 - 16 SPIE (2005) Vol 5755 - 16
March. 2005 Models for reticle performance Page -2-SPIE (2005) Vol. 5755_16
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• Introduction Physical Process Window description and Perturbations
• The Best Focus Feature Contour Formalization Removal of metrology and exposure systematic error Examples
• Duty Cycle• BARC• High k1 applications
• Full-Field Process Window Optimum Field Response
• With tool defocus removed• Depth of Focus & Focus Contours
• Application to Full-Wafer responses Formalization Addressing Film and Feature systematic Exposure tool artifacts
• Final Note Exposure artifact influence on the Process Window
• Conclusions
• Introduction Physical Process Window description and Perturbations
• The Best Focus Feature Contour Formalization Removal of metrology and exposure systematic error Examples
• Duty Cycle• BARC• High k1 applications
• Full-Field Process Window Optimum Field Response
• With tool defocus removed• Depth of Focus & Focus Contours
• Application to Full-Wafer responses Formalization Addressing Film and Feature systematic Exposure tool artifacts
• Final Note Exposure artifact influence on the Process Window
• Conclusions
Models for Reticle Performance
March. 2005 Models for reticle performance Page -3-SPIE (2005) Vol. 5755_16
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Two-variable process window
• The number of un-Collapsed lines visible in a group were rated from SEM photos ranging from 0 to “7”
• Results are shown for an 80 nm feature width
mn
SN
n nm
M
m
FE
EaCD
10
0
BCD
Collapsed line
March. 2005 Models for reticle performance Page -4-SPIE (2005) Vol. 5755_16
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Properties of the PW Surface
a00 Feature size at optimum dose and focus
a10 The dose sensitivity or change of features size with dose being inversely proportional to exposure latitude.
a20 Rate of change of dose sensitivity with dose
a02 Defocus sensitivity of the feature
a12 Dose & defocus coupling
mn
SN
n nm
M
m
FE
EaCD
10
0
C. Ausschnitt et al SPIE 5378 p38-47
C. Mack et al SPIE 5038-39
C. Ausschnitt et al SPIE 5378 p38-47
C. Mack et al SPIE 5038-39
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CD-SEM with PW CD vs Dose
CD vs Focus
Optimum Focus(for this case)
deFocus1. CD vs Dose is not
linear
2. Surface “fit” quality can vary!
March. 2005 Models for reticle performance Page -6-SPIE (2005) Vol. 5755_16
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Why “Process Window” fit-quality varies?
• Primary disturbances causing CD Uniformity (CDU) variations grouped upon their sources.
Reticle Scanner Track & Process
Effective Focus
Wafer flatness
Device topography
Substrate
BARC coat
Resist Film coat
PEB Temp & Time
Develop
Exposure Dose
Slit Uniformity
Focus SetUp
Chuck Flatness
Up-Down Scan
CDUEffective Dose
Scan Linearity
CD’s
Flatness
Transmission
March. 2005 Models for reticle performance Page -7-SPIE (2005) Vol. 5755_16
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Best Focus – Feature Contour
• Derive CD @ Dose & Best Focus
• Relationship functional for Feature Widths Side Wall Angle (SWA) Resist & BARC thickness Line Edge Roughness
01* 1
01
mn
SN
n nm
M
m
FE
Eam
F
CDBest Focus (for Critical Dimension or CD)
Set derivative = 0 & solve for “F”
CD @ Best Focus
March. 2005 Models for reticle performance Page -8-SPIE (2005) Vol. 5755_16
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Dose Response of Best Focus (BF) & CD
• Feature vs Dose Will be near-linear if feature profiles are well resolved
• Best Focus vs Dose Slope should be ~0 if lens is near aberration free and
films do not influence focus response
Best Focus
Dose
March. 2005 Models for reticle performance Page -9-SPIE (2005) Vol. 5755_16
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Example #1 – Duty cycle• 140 nm contacts
• 3 sets of pitch
• CD-SEM measured
p240
p550
p420
TCL=140nmcontact
Best Focus
March. 2005 Models for reticle performance Page -10-SPIE (2005) Vol. 5755_16
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Example 2: BARC Performance
• The ARC 3 data has a lower CD vs dose, reducing it’s sensitivity to dose A greater target dose to obtain CD size of 80 nm A strong sensitivity of best focus to the dose
Best Focus Size_at_BF DoF DoseMean: 0.1230 79.2 0.5420 25Max: 0.1230 79.2 0.5420 25Min: 0.1230 79.2 0.5420 25
Best Focus Size_at_BF DoF DoseMean: 0.1040 79.2 0.5200 23.5Max: 0.1040 79.2 0.5200 23.5Min: 0.1040 79.2 0.5200 23.5
ARC3 at Best DoseNo ARC at Best Dose
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Example #3; Pushing the envelope
• Dose values are arbitrary• At 80 nm, we are driving the imaging capabilities of the lens• Note response of BF to scan & lens aberrations• Response is caused by wavefront asymmetry and results in
feature line edge asymmetry
Site 15 Site 30
Response for 80 nm, 193 litho process
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Consider the Process Window
• A CD-SEM based data sample of the process window
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Scatterometry Process Window Side Wall AngleWhat can we learn?
Dose= 18 19 20 21 22 23 24
Focus-0.24
-0.16
-0.08
0.0
+0.08
+0.16
+0.24
Process Window
• Exposures• 193nm litho process for 100nm
features– AT1100 scanner, 0.75NA with annular
illumination– 90nm gratings at 1:1 with full field
coverage– 240nm resist on 78nm Barc on Si
• OCD metrology: NI, rotating polarized light (Nano9030)
• diffractive optical metrology (scatterometry) - outputs spectral intensity changes of 0th order diffracted light intensity
Weir PW Software from TEA Systems
March. 2005 Models for reticle performance Page -14-SPIE (2005) Vol. 5755_16
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Optimal BCD Image
• BCD values as estimated for the reticle• Across-field Focus and metrology errors removed by process• Note that these values include both reticle offsets and exposure/lens aberrations
BCD Contour Plot
X (slit) location (mm)
Y (
scan
) lo
cati
on (
mm
)
BCD Vector Plot
mn
SN
n nm
M
m
FE
EayxFR
1),(0
0
mn
SN
n nm
M
m
FE
EayxFR
1),(0
0
100 nm 1:1, 90nm TCD100 nm 1:1, 90nm TCD
March. 2005 Models for reticle performance Page -15-SPIE (2005) Vol. 5755_16
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Optimum Field Response thru Dose
• BCD summarizes natural feature size response @ best Focus for each dose
• DoF computed when in control
Best Focus BCD4 (nm) DoF DoseMean: 0.0070 104.1780 18.0
Max: 0.0810 110.6640 18.0Min: -0.1570 100.6540 18.0IFD: 0.2380 10.0100 18.0
Mean: 0.0180 94.3450 0.0530 19.0Max: 0.0830 99.8950 0.0530 19.0Min: -0.1340 91.0560 0.0530 19.0IFD: 0.2170 8.8390 0.0000 19.0
Mean: 0.0330 84.4540 0.3560 20.0Max: 0.0940 88.9940 0.5970 20.0Min: -0.0740 81.4100 0.1710 20.0IFD: 0.1680 7.5840 0.4260 20.0
Mean: 0.1080 72.8100 0.6260 21.0Max: 0.9820 77.6260 0.6400 21.0Min: -0.1050 30.3330 0.5230 21.0IFD: 1.0870 47.2940 0.1170 21.0
Best Focus BCD4 (nm) DoF DoseMean: -0.0390 65.3970 0.0160 22.0
Max: 0.2880 70.2900 0.0210 22.0Min: -0.2800 61.7610 0.0110 22.0IFD: 0.5680 8.5290 0.0100 22.0
Mean: -0.0840 56.2490 23.0Max: -0.0320 59.1160 23.0Min: -0.1570 53.4410 23.0IFD: 0.1250 5.6740 23.0
Mean: -0.0570 46.2440 24.0Max: 0.0210 47.9520 24.0Min: -0.1340 43.7280 24.0IFD: 0.1550 4.2230 24.0
Best Focus BCD4 (nm) DoF DoseMean: -0.0390 65.3970 0.0160 22.0
Max: 0.2880 70.2900 0.0210 22.0Min: -0.2800 61.7610 0.0110 22.0IFD: 0.5680 8.5290 0.0100 22.0
Mean: -0.0840 56.2490 23.0Max: -0.0320 59.1160 23.0Min: -0.1570 53.4410 23.0IFD: 0.1250 5.6740 23.0
Mean: -0.0570 46.2440 24.0Max: 0.0210 47.9520 24.0Min: -0.1340 43.7280 24.0IFD: 0.1550 4.2230 24.0
March. 2005 Models for reticle performance Page -16-SPIE (2005) Vol. 5755_16
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Metrology & Process Independent CharacteristicsFocus
Uniformity
Depth of Focus Uniformity
March. 2005 Models for reticle performance Page -17-SPIE (2005) Vol. 5755_16
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CD-SEM ReticleMEF+ = 4.3292
Optimized BCD from Wafer
Nanometrics ReticleMEF+ = 4.305813
Validation; wafer vs Reticle 5754-110 Poster5754-110 Poster
March. 2005 Models for reticle performance Page -18-SPIE (2005) Vol. 5755_16
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BCD, TCD, SWA @ Best Focus/Dose
March. 2005 Models for reticle performance Page -19-SPIE (2005) Vol. 5755_16
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BARC modeled wafer uniformityDusa et al. SPIE Vol. 5378-11 Dusa et al. SPIE Vol. 5378-11
March. 2005 Models for reticle performance Page -20-SPIE (2005) Vol. 5755_16
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T3 (PR)
TCD
SWABARC
Derived variable distributions across the wafer
BCD
March. 2005 Models for reticle performance Page -21-SPIE (2005) Vol. 5755_16
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BCD & TCD Size vs PhotoResist
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BARC Thickness & SWA
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Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 1.5- + - + - + -
+ - + - + - + Reticle Scan Direction
+
-
Scan Direction Artifacts
March. 2005 Models for reticle performance Page -24-SPIE (2005) Vol. 5755_16
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Profile variation with Focus
Bottom CD
Slope
Top CD- + - + - + -
+ - + - + - +
Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 +1.5Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 +1.5 Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 +1.5Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 +1.5
- + - + - + -
+ - + - + - +
Scan direction
Process window
Lens After cleaningLens Before cleaning
See Poster: 5754-87See Poster: 5754-87
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Slope vs Dose across the slit
5 18 19 6
Lens After cleaningLens Before cleaning
9 10 11 12
Up +ScanUp +Scan
Down -ScanDown -Scan
March. 2005 Models for reticle performance Page -26-SPIE (2005) Vol. 5755_16
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Reticle Scan Removed
Bottom CD
Slope
Top CD
Reticle scan-stage component removed.
Provides view of lens perturbations
- + - + - + -
+ - + - + - +
Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 +1.5Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 +1.5
- + - + - + -
+ - + - + - +
Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 +1.5Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 +1.5
Lens After cleaningLens Before cleaning
March. 2005 Models for reticle performance Page -27-SPIE (2005) Vol. 5755_16
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Lens Slit Removed
Bottom CD
Slope
Top CD- + - + - + -
+ - + - + - +
Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 +1.5
Lens After cleaningLens Before cleaning
- + - + - + -
+ - + - + - +
Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 +1.5
Lens aberrations removed.
Provides view of scan uniformity
Scan speed nonlinearity start/end of scan
- + - + - + -
+ - + - + - +
- + - + - + -
+ - + - + - +
March. 2005 Models for reticle performance Page -28-SPIE (2005) Vol. 5755_16
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FR(x,y) @ Best FocusCD response after field focus
errors are removed.
TopCD
BottomCD
Slope
-Down + Up-Down + Up
Lens After cleaningLens Before cleaning-Down + Up-Down + Up
March. 2005 Models for reticle performance Page -29-SPIE (2005) Vol. 5755_16
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A Note: Exposure artifacts & the model
• Be aware of scan artifacts such as stage scan direction perturbations
mn
SN
n nm
M
m
FE
EaCD
10
0
mn
m mFaCD
0
March. 2005 Models for reticle performance Page -30-SPIE (2005) Vol. 5755_16
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Summary• Process Window surface models
The algorithm history extends through several formats Extended to Dose Response of Features independent of metrology & Field
focus Best Focus vs Dose
• Plot yields additional information on process response and extensibility
• Full-Field Process Window Provides the optimum feature response across the field Traceable directly to reticle measurements Can be extended to Depth of Focus and deFocus contours
• Full Wafer Response Implements Best Feature response of the Full-Field Process Window Models were shown for addressing wafer-systematic perturbations
• Scanner-specific field models shown in paper 5754-110 Systematic feature response perturbations
• Response to Film and and exposure tool artifacts Final Note
• Exposure tool induced perturbations can directly influence the accuracy of the process window calculation
SPIE (2005) Vol. 5755_16
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End of Presentation – Thank You
• Please visit posters: “Feature profile control and the influence of scan artifacts”
• 5754-87
“Models for reticle performance and comparison of direct measurement ” • 5754-110
Visit us at:
http://www.TEAsystems.comBARC
Uniformity
March. 2005 Models for reticle performance Page -32-SPIE (2005) Vol. 5755_16
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SPIE (2005) Vol. 5755_16
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Background and additional slides
March. 2005 Models for reticle performance Page -34-SPIE (2005) Vol. 5755_16
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(2)
Formalization of the Spatial Signatures
• - IFp(x,y): IntraField periodic signature reticle component and a systematic –within-wafer, periodic
component describing the scanner field (slit and scan signatures)
• - Wp (x,y): feature response variability This component is primarily a result of the “whole-wafer-at-a-
time” process steps, characteristic to resist and track.
• - DD (x,y): Die-to-Die variability variations in discrete scanning disturbances such as effective
dose, the incidental focus or scan direction.
• - r: the residual component
(1)•Feature Response to process disturbance “m” • is the sensitivity coefficient
Ref. 2: Mircea Dusa et al, “Intra-wafer CDU characterization … ”, Proc. SPIE (2004), Vol. 5378-11
Most complex signature
March. 2005 Models for reticle performance Page -35-SPIE (2005) Vol. 5755_16
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Component Analysis of MEF
• Definition MEF = Mask Error Function
• In terms if IntraField Periodic SignatureIFp(x,y) = IFReticle+IFSlit, scan aberrations + IFeffective Dose,Focus + IFResist + IFflare,scatter +Ifscatter
MEF
Objective: Identify the MEF Components of IFp
Reduction) *CDmask (
CDresist MEF
March. 2005 Models for reticle performance Page -36-SPIE (2005) Vol. 5755_16
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IntraField (IFp) Signature
• IFslit Perturbations
Lens aberrations Flare, scatter, proximity etc. Photoresist artifacts
• IFScan Reticle Stage Distortions: effective dose
• scan speed Effective Focus
• Stage pitch, yaw tilt• travel height-offset
• IFReticle
Effective feature width
Photomask Processing
rIFIFIFyxIF ticleScanSlitp Re),(
4
01 j
jj
n
ColumnScan ryaIF
IFslit= Lens Aberrations
4
0
)(n
nn
Rowsjslit xaxWLIF
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Lens-Slit Model, Row offsets
• Modeled offset of each slit position• Repeatability of each reticle scan’s travel• Contributing about 1 nm of noise to BCD
error budget
Focus offsets
4
0
)(n
nn
Rowsj xaxWL
•Lens-slit model is applied to every row of every field of the wafer. Results are summarized on the right.
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Right-side average
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Average Field
March. 2005 Models for reticle performance Page -41-SPIE (2005) Vol. 5755_16
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BCD Raw Data
March. 2005 Models for reticle performance Page -42-SPIE (2005) Vol. 5755_16
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Modeled BCD-RET across wafer
March. 2005 Models for reticle performance Page -43-SPIE (2005) Vol. 5755_16
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Profile Response @ Best Focus (Before)
Bottom CDUP+ Scan Best Focus Size_at_BF DoF
Mean: 0.0580 157.5 0.1610Max: 0.3280 175.2 0.2070Min: -0.1170 146.5 0.1330IFD: 0.4450 28.7 0.0740
Down - Bottom CDScan Best Focus Size_at_BF DoF
Mean: 0.0300 158.6 0.2010Max: 0.5630 185.5 0.3870Min: -0.2120 143.5 0.1200IFD: 0.7750 42.0 0.2670
Top CDUp+ Best Focus Size_at_BF DoFMean: 0.0740 131.1 0.1870
Max: 0.1570 151.3 0.2600Min: 0.0000 113.3 0.0930IFD: 0.1570 38.0 0.1670
Top CDDown - Best Focus Size_at_BF DoF
Mean: 0.0320 129.8 0.2240Max: 0.1460 149.2 0.4000Min: -0.1010 100.6 0.1200IFD: 0.2470 48.6 0.2800
SlopeDown - Best Focus Size_at_BF DoF
Mean: 0.0030 87.6 0.2130Max: 0.0490 89.4 0.3530Min: -0.0330 85.5 0.0200IFD: 0.0820 3.8 0.3330
SlopeUp + Best Focus Size_at_BF DoF
Mean: 0.0240 87.8 0.2570Max: 0.0580 89.2 0.3270Min: -0.0220 86.8 0.1600IFD: 0.0800 2.4 0.1670
UP +Scan Down -ScanLens before cleaning
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Profile Response @ Best Focus (After)
Up + Best FocusBottomCD
at BF DoFMean: 0.0080 171.6 0.3850
Max: 0.0870 183.2 0.4000Min: -0.0710 163.5 0.3330IFD: 0.1580 19.8 0.0670
Up + FocusSlope Slope DoF_SlopeMean: 0.0180 87.6 0.2150
Max: 0.1190 88.7 0.4000Min: -0.0700 86.4 0.0470IFD: 0.1890 2.3 0.3530
Down - FocusSlope Slope DoF_SlopeMean: 0.0340 87.5 0.1480
Max: 0.1530 88.9 0.3470Min: -0.0520 86.5 0.0270IFD: 0.2050 2.4 0.3200
Down - FocusBCDBottomCD
at BF DoF_BCDMean: 0.0160 174.0 0.3350
Max: 0.0750 216.8 0.4000Min: -0.0400 157.3 0.1470IFD: 0.1150 59.5 0.2530
Up+ Best Focus Top CD DoFMean: 0.0010 142.5 0.3810
Max: 0.0710 159.0 0.4000Min: -0.0460 121.2 0.3130IFD: 0.1170 37.8 0.0870
Down - Best Focus Top CD DoFMean: -0.0240 144.2 0.3720
Max: 0.0640 173.0 0.4000Min: -0.1870 119.7 0.2330IFD: 0.2510 53.3 0.1670
Lens After cleaningUP +Scan Down -Scan
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Focus Uniformity
-Down + Up-Down + Up
BottomCD
TopCD
Slope
Lens After cleaningLens Before cleaning
BottomCD
Calculated fromTopCD
Slope
-Down + Up-Down + UpCalculated
from
March. 2005 Models for reticle performance Page -46-SPIE (2005) Vol. 5755_16
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DoF Variation
TopCD
BottomCD
After Clean• Both features plot to the same scale• Note however there is a problem with the lower left
corner of the field with a shallow DoF Partially hidden here by the scale
-Down + Up-Down + Up
Lens After cleaningLens Before cleaning
-Down + Up-Down + Up
March. 2005 Models for reticle performance Page -47-SPIE (2005) Vol. 5755_16
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Lens-Slit Uniformity
• The piston BCD value of each columns yield a representation of the BCD perturbation caused by the lens.
• This is the Average Field• Variation show is caused by the 8 focus-
shifted fields• Slit contributes about 2 nm to error budget
March. 2005 Models for reticle performance Page -48-SPIE (2005) Vol. 5755_16
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Average Field BCD Scan Profile
• Boxplot across Reticle Scan shown• Reticle & Wafer errors removed• The right-side (bottom) of the scan’s
mid-points has been averaged and transposed to the left-side (top) graph. Note the left-right pitch of the reticle-
scan’s travel accounting for approximately 1 nm of variation
Right-side average
March. 2005 Models for reticle performance Page -49-SPIE (2005) Vol. 5755_16
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Slit Wobble
• Slit-wobble is contributing about 1.25 nm to error budget
• Tilt contributes 3 nm to budget
March. 2005 Models for reticle performance Page -50-SPIE (2005) Vol. 5755_16
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IntraField Process Window
• W(x,y) = Feature Response located at (x,y) on reticle
• Process window reduction
• Site #8 Soft data-sport Easily corrected and handled
• Site #6 response Reticle Error Lens and/or scan aberrations
(MEF)
Site #8
Site #6
mn
SN
n nm
M
m
FE
EayxW
1),(0
0
mn
SN
n nm
M
m
FE
EayxW
1),(0
0
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Models for reticle performance• Introduction
• Formalized MEF derivation Influence of process and exposure Method of analysis
• Phase I Evaluation of effective focus & dose Full-profile response Characterization
• SEM, OCD
MEF calculation from SEM & OCD
• Phase II Full wafer response Process variation analysis ARC volatility Response wrt theory of CD vs Arc
• Summary• Process perturbation to feature profile error budget
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Focus uniformityDose = 20 21 (isofocal) 22 23
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Experimental conditions• Exposures
• typical 193nm litho process for 100nm features– AT1100 scanner, 0.75NA with annular illumination– 90nm gratings at 1:1 with full field coverage– 240nm resist on 78nm Barc on Si
• OCD metrology: NI, rotating polarized light (Nano9030)• diffractive optical metrology (scatterometry) - outputs spectral intensity changes of
0th order diffracted light intensity
• modeled grating parameters– bottom CD; – resist thickness (Tr) and Sidewall Angle (SWA)– bottom arc thickness (Tbarc)– mean square errror (MSE)
• Calculate BCD at optimum focus and dose Weir PW Software from TEA Systems Determine BCD surface across field with removal of focus errors
R R R R RTE TM TE TM( ) cos ( ) sin ( ) cos( ) sin ( ) cos ( ) 4 4 2 22
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Center slit response
• Determine Best focus for each site from 1st order derivative of each BCD vs Focus curve
mn
SN
n nm
M
m
FE
EayxW
1),(0
0
mn
SN
n nm
M
m
FE
EayxW
1),(0
0
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Analysis of Reticle-free CD’s
• Wafer 177 New metrology tool Fixed focus with selected sites
at +/-1% dF and +/-2% dF as shown
• Measured BCD, BARC, SWA & Photoresist
• 121 (11x11) points per field
Measured field sites
Layout with Focus offsets (in um) shown
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BCD as measured
Wafer damaged area
Bad site measurement
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BCD with Reticle errors removed
• BCD variation from film, focus and exposure variations
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BCD-RET vs PhotoResist
• RET has been removed
• Typical CD vs photoresist thickness curve Illustrates the Photoresist ablation from exposure & develope
March. 2005 Models for reticle performance Page -59-SPIE (2005) Vol. 5755_16
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BCD-RET vs BARC
• This is for the field edges.
March. 2005 Models for reticle performance Page -60-SPIE (2005) Vol. 5755_16
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SWA vs BARC
• As expected, BARC thickness has a strong influence on the profile
March. 2005 Models for reticle performance Page -61-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
PW spatial viewTarget
• 90 nm feature
• +/- 10% EL
Dose= 18 19 20 21 22 23 24
Focus-0.24
-0.16
-0.08
0.0
+0.08
+0.16
+0.24Focus Dose= 18 19 20 21 22 23 24
-0.24 7 7 7-0.16 7 7 7 7 7-0.08 7 7 7 7 7 7 7
0 7 7 7 7 7 7 70.08 7 7 7 7 7 7 70.16 7 7 7 7 70.24 7 7 7
Focus Dose= 18 19 20 21 22 23 24-0.24 7 7 7-0.16 7 7 7 7 7-0.08 7 7 7 7 7 7 7
0 7 7 7 7 7 7 70.08 7 7 7 7 7 7 70.16 7 7 7 7 70.24 7 7 7
March. 2005 Models for reticle performance Page -62-SPIE (2005) Vol. 5755_16
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Focus-response Field Center
• Center-site of exposure for each dose
March. 2005 Models for reticle performance Page -63-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
Dose Response at best focus
• Optimum CD vs Dose curve for entire field• Focus errors across slit have been removed• Dose response is now linear
This assumes a flat field since focus is optimized at each individual site
CD vs Dose at Best Focus
BCD = -8.2515D + 256.98
60.065.070.075.080.085.090.095.0
100.0105.0110.0
18.0 18.5 19.0 19.5 20.0 20.5 21.0 21.5 22.0 22.5 23.0 23.5 24.0
Dose
BC
D3
(n
m)
March. 2005 Models for reticle performance Page -64-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
Center Slit: Focus & DoF Response • DoF = red
• Best Focus = blue
Feature @ ResidualsDose Site Best Focus Best Focus DoF Offset Slope Quadratic Sigma20.0000 13.0000 -0.0350 95.1576 0.2910 95.4140 14.9460 228.5280 1.945020.0000 14.0000 -0.0720 94.1776 0.1130 95.4230 37.0100 308.2390 1.391020.0000 15.0000 -0.0970 91.0807 0.3820 93.0710 40.2300 195.2410 1.452020.0000 16.0000 -0.0500 90.0853 0.0000 90.4680 15.2480 151.9880 0.992020.0000 17.0000 -0.0490 90.4063 0.4340 90.9160 21.3040 233.8330 1.721020.0000 18.0000 -0.0270 90.8636 0.5180 91.0340 13.3960 284.3020 2.7540
-0.120
-0.100
-0.080
-0.060
-0.040
-0.020
0.000
12 13 14 15 16 17 18 19
Location on slit
Bes
t F
ocu
s (u
m)
0.00
0.10
0.20
0.30
0.40
0.50
0.60
Do
F (
um
)
•Each site exhibits a unique value for optimum focus & Depth of Focus (DoF)
•Use Feature Size, independent of focus, to determine MEF
13 14 15 16 17 18
March. 2005 Models for reticle performance Page -65-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
BCD final (nm)
• Reticle values have been removed from the BCD metrology• Note residual of reticle image on gossly overexposed 24 mj column
Dose= 18 19 20 21 22 23 24
Focus-0.24
-0.16
-0.08
0.0
+0.08
+0.16
+0.24
Invalid data
March. 2005 Models for reticle performance Page -66-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
BCD Final Field
• BCD values as estimated for the reticle• Across-field Focus and metrology errors removed by process• Note that these values include both reticle offsets and exposure/lens aberrations
March. 2005 Models for reticle performance Page -67-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
Average Hitachi Field
March. 2005 Models for reticle performance Page -68-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
Nanometrics OCD Measured Reticle
• Nanometrics OCD Direct measurement of Reticle 400 nm patterns
X (slit) location (mm)
Y (
scan
) lo
cati
on (
mm
)
March. 2005 Models for reticle performance Page -69-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
Reticle Scan Model
• Field-by-field Reticle-Scan Model
• Wafer model removed
6
1
),(m
mmxjj ycWLyxW
March. 2005 Models for reticle performance Page -70-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
Reticle-scan piston
• BCD Piston (offset) term for each modeled scan (column)
• Note the locations of the focus shifts and the corresponding shift in average field value Reaction may actually be more scan-
direction dependant
March. 2005 Models for reticle performance Page -71-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
Models for reticle performance• Introduction
• MEF Formaization Influence of process and exposure Method of analysis
• Phase I Evaluation of effective focus & dose Full-profile response Characterization
• SEM, OCD
MEF calculation from SEM & OCD
• Phase II Full wafer response Process variation analysis ARC volatility Response CD vs Arc
• Summary• Process perturbation to feature profile error budget
March. 2005 Models for reticle performance Page -72-SPIE (2005) Vol. 5755_16
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BARC modeled wafer uniformity
March. 2005 Models for reticle performance Page -73-SPIE (2005) Vol. 5755_16
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BCD vs BARC
• All exposures
March. 2005 Models for reticle performance Page -74-SPIE (2005) Vol. 5755_16
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Residuals to modeled wafer
March. 2005 Models for reticle performance Page -75-SPIE (2005) Vol. 5755_16
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Average Field BCD Slit Profile
• Boxplot across slit & Scan shown
March. 2005 Models for reticle performance Page -76-SPIE (2005) Vol. 5755_16
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Row and Slit profile
• Nano-Day1 Data
• Slit & Scan signatures of tool
• Estimate of reticle errors Includes reticle plus focus & exposure perturbations
Slit Signature
Scan Signature
March. 2005 Models for reticle performance Page -77-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
Lens Slit Model – slit wobble
• BCD-RET data showing slit tilt or “wobble” during the scan sequence
March. 2005 Models for reticle performance Page -78-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
BCD Reticle-Scan Tilt & Curvature
• High BCD values at end of scan are most likely due to the slit-scan speed changes.
• Reticle-scanning is responsible for 1.7 nm of the BCD budget.
SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
Layouts for Figures in Text
March. 2005 Models for reticle performance Page -80-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
• W(x,y) = Feature Response located at (x,y) on reticle
• Process window reduction
• Site #8 Soft data-sport Easily corrected and handled
• Site #6 response Reticle Error Lens and/or scan aberrations
(MEF)
Site #8
Site #6
March. 2005 Models for reticle performance Page -81-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
mn
SN
n nm
M
m
FE
EayxW
1),(0
0
mn
SN
n nm
M
m
FE
EayxW
1),(0
0
March. 2005 Models for reticle performance Page -82-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
Dose Response at best focus
• Optimum CD vs Dose curve for entire field• Focus errors across slit have been removed• Dose response is now linear
This assumes a flat field since focus is optimized at each individual site
CD vs Dose at Best Focus
BCD = -8.2515D + 256.98
60.065.070.075.080.085.090.095.0
100.0105.0110.0
18.0 18.5 19.0 19.5 20.0 20.5 21.0 21.5 22.0 22.5 23.0 23.5 24.0
Dose
BC
D3
(n
m)
March. 2005 Models for reticle performance Page -83-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
Average Field BCD Scan Profile
• Boxplot across Reticle Scan shown• Reticle & Wafer errors removed• The right-side (bottom) of the scan’s
mid-points has been averaged and transposed to the left-side (top) graph. Note the left-right pitch of the reticle-
scan’s travel accounting for approximately 1 nm of variation
Right-side average
March. 2005 Models for reticle performance Page -84-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
Analysis of Reticle-free CD’s
• Wafer 177 New metrology tool Fixed focus with selected sites
at +/-1% dF and +/-2% dF as shown
• Measured BCD, BARC, SWA & Photoresist
• 121 (11x11) points per field
Measured field sites
Layout with Focus offsets (in um) shown
March. 2005 Models for reticle performance Page -85-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
BCD as measured
Wafer damaged area
Bad site measurement
March. 2005 Models for reticle performance Page -86-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
BCD with Reticle errors removed
• BCD variation from film, focus and exposure variations
March. 2005 Models for reticle performance Page -87-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
BCD-RET vs PhotoResist
• RET has been removed
• Typical CD vs photoresist thickness curve Illustrates the Photoresist ablation from exposure & develope
March. 2005 Models for reticle performance Page -88-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
BCD-RET vs BARC
• This is for the field edges.
March. 2005 Models for reticle performance Page -89-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
Lens-Slit Model, Row offsets
• Modeled offset of each slit position• Repeatability of each reticle scan’s travel• Contributing about 1 nm of noise to BCD
error budget
Focus offsets
4
0
)(n
nn
Rowsj xaxWL
•Lens-slit model is applied to every row of every field of the wafer. Results are summarized on the right.
March. 2005 Models for reticle performance Page -90-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
Focus offsets
4
0
)(n
nn
Rowsj xaxWL
March. 2005 Models for reticle performance Page -91-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
Lens Slit Model – slit wobble
• BCD-RET data showing slit tilt or “wobble” during the scan sequence
March. 2005 Models for reticle performance Page -92-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
Slit Wobble
• Slit-wobble is contributing about 1.25 nm to error budget
• Tilt contributes 3 nm to budget
March. 2005 Models for reticle performance Page -93-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
SWA; Residuals to wafer modelNote fine structure, due to scan?
March. 2005 Models for reticle performance Page -94-SPIE (2005) Vol. 5755_16
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Mean Field ValuesBCD TCD SWA
T2(ARC) T3 (PR) MSE
March. 2005 Models for reticle performance Page -95-SPIE (2005) Vol. 5755_16
TEA Systems, Inc.
Raw MSE & PR
Best Focus Size_at_BF DoF DoseMean: 0.1230 79.2 0.5420 25Max: 0.1230 79.2 0.5420 25Min: 0.1230 79.2 0.5420 25
Best Focus Size_at_BF DoF DoseMean: 0.1040 79.2 0.5200 23.5Max: 0.1040 79.2 0.5200 23.5Min: 0.1040 79.2 0.5200 23.5
ARC3 at Best DoseNo ARC at Best Dose
Site 15 Site 30
Dose= 18 19 20 21 22 23 24
Focus-0.24
-0.16
-0.08
0.0
+0.08
+0.16
+0.24
Process Window
CD-SEM SWA - Scatterometry
• BCD values as estimated for the reticle• Across-field Focus and metrology errors removed by process• Note that these values include both reticle offsets and exposure/lens aberrations
BCD Contour Plot
X (slit) location (mm)
Y (
scan
) lo
cati
on (
mm
)
BCD Vector Plot
mn
SN
n nm
M
m
FE
EayxFR
1),(0
0
mn
SN
n nm
M
m
FE
EayxFR
1),(0
0
100 nm 1:1, 90nm TCD100 nm 1:1, 90nm TCD
Best Focus BCD4 (nm) DoF DoseMean: 0.0070 104.1780 18.0
Max: 0.0810 110.6640 18.0Min: -0.1570 100.6540 18.0IFD: 0.2380 10.0100 18.0
Mean: 0.0180 94.3450 0.0530 19.0Max: 0.0830 99.8950 0.0530 19.0Min: -0.1340 91.0560 0.0530 19.0IFD: 0.2170 8.8390 0.0000 19.0
Mean: 0.0330 84.4540 0.3560 20.0Max: 0.0940 88.9940 0.5970 20.0Min: -0.0740 81.4100 0.1710 20.0IFD: 0.1680 7.5840 0.4260 20.0
Mean: 0.1080 72.8100 0.6260 21.0Max: 0.9820 77.6260 0.6400 21.0Min: -0.1050 30.3330 0.5230 21.0IFD: 1.0870 47.2940 0.1170 21.0
Best Focus BCD4 (nm) DoF DoseMean: 0.0070 104.1780 18.0
Max: 0.0810 110.6640 18.0Min: -0.1570 100.6540 18.0IFD: 0.2380 10.0100 18.0
Mean: 0.0180 94.3450 0.0530 19.0Max: 0.0830 99.8950 0.0530 19.0Min: -0.1340 91.0560 0.0530 19.0IFD: 0.2170 8.8390 0.0000 19.0
Mean: 0.0330 84.4540 0.3560 20.0Max: 0.0940 88.9940 0.5970 20.0Min: -0.0740 81.4100 0.1710 20.0IFD: 0.1680 7.5840 0.4260 20.0
Mean: 0.1080 72.8100 0.6260 21.0Max: 0.9820 77.6260 0.6400 21.0Min: -0.1050 30.3330 0.5230 21.0IFD: 1.0870 47.2940 0.1170 21.0
Best Focus BCD4 (nm) DoF DoseMean: -0.0390 65.3970 0.0160 22.0
Max: 0.2880 70.2900 0.0210 22.0Min: -0.2800 61.7610 0.0110 22.0IFD: 0.5680 8.5290 0.0100 22.0
Mean: -0.0840 56.2490 23.0Max: -0.0320 59.1160 23.0Min: -0.1570 53.4410 23.0IFD: 0.1250 5.6740 23.0
Mean: -0.0570 46.2440 24.0Max: 0.0210 47.9520 24.0Min: -0.1340 43.7280 24.0IFD: 0.1550 4.2230 24.0
Best Focus BCD4 (nm) DoF DoseMean: -0.0390 65.3970 0.0160 22.0
Max: 0.2880 70.2900 0.0210 22.0Min: -0.2800 61.7610 0.0110 22.0IFD: 0.5680 8.5290 0.0100 22.0
Mean: -0.0840 56.2490 23.0Max: -0.0320 59.1160 23.0Min: -0.1570 53.4410 23.0IFD: 0.1250 5.6740 23.0
Mean: -0.0570 46.2440 24.0Max: 0.0210 47.9520 24.0Min: -0.1340 43.7280 24.0IFD: 0.1550 4.2230 24.0
CD-SEM ReticleMEF+ = 4.3292
Optimized BCD from Wafer
Nanometrics ReticleMEF+ = 4.305813
Focus Uniformity
Depth of Focus Uniformity
T3 (PR)TCD SWABARCBCD
Bottom CD
Top CD- + - + - + -
+ - + - + - +
Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 +1.5Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 +1.5
- + - + - + -
+ - + - + - +
Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 +1.5Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 +1.5
Lens After cleaningLens Before cleaning
Slope
Bottom CD
Slope (SWA)
Top CD- + - + - + -
+ - + - + - +
Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 +1.5
Lens After cleaningLens Before cleaning
- + - + - + -
+ - + - + - +
Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 +1.5
Scan speed nonlinearity start/end of scan
- + - + - + -
+ - + - + - +
- + - + - + -
+ - + - + - +
mn
SN
n nm
M
m
FE
EaCD
10
0
mn
m mFaCD
0