Copyright 2001, Society of Photo-Optical Instrumentation Engineers This poster was presented at SPIE as presentation number 4346-72 and is made available as an electronic reprint with permission of SPIE. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.

Multiple Pitch Transmission and Phase Analysis of Six Types of Strong Phase-Shifting Masks

John S. Petersena, David J. Gerolda, and Marc. D. Levensonb

aPetersen Advanced Lithography, Inc. 8834 N. Capital of Texas Highway, #304, Austin, TX 78759

bM.D. Levenson Consulting19868 Bonnie Ridge Way, Saratoga, CA 95070

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PSM Topography and Dual Trenches

A perfectly manufactured phase-shifting mask has an intensity imbalance between the shifted and unshifted intensity peaks.Adding a dual trench corresponding to a global phase shift of πradians can equalize the peaks.

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More important, however, is the behavior of the shifted and unshifted peaks through focus.Note that the dual trench has shifted the intensity peaks apart.The peak equalization is therefore stymied out of focus.This means is an insufficient model.

Phase Error

defocus = -0.5 um

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best focus

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00.20.40.60.8

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λπφ /)1(2 −=∆ nt

J. S. Petersen, et.al., SPIE Vol. 3564, p. 288 (1998)

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Variations on the Theme

Additive

Side Chrome

Dual TrenchUndercut

Selective Biasing

Dual Trench w/ Undercut

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Imaging Comparison: Uncompensated SCAA vs. 2 Common Corrections

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Aeria l Image Intens ity

Horizontal Position (nm)

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Ae ria l Ima ge Inte ns ity

Horizonta l Pos ition (nm)

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Horizonta l Pos ition (nm)

Defocus(microns)

100 nm L/S pattern imaged at 248 nm with NA=0.744, σ=0.2, k1=0.3. ProMAX/2D & PROLITH/2

E-Fi

elds

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ial I

mag

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SCAAM Dual-trench Undercut

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Alternating PSM Topography Design

Build x-z slice of AltPSMUsing “geometric” phase depth

(based on bulk n & k parameters)

Simulate EMF @ 300nm pitch

Extract phase and transmission errors

Study aerial image using PROLITH and grayscale maskComplete?

Adjust mask topographyMinimized? NoYes

Export grayscale mask (intensity

and phase below mask) to PROLITH

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EMF Simulator Z-step Choice

Simulator �accuracy� = �(grid size)! Test: Standing wave size in homogeneous index = 1,0

slab! Results:

" ProMAX - errors reduce with finer grid to at least 500 steps/λ" TEMPESTp � errors reduce to limit of 73 steps/ λ

(3.4nm @248nm)" But step size limit does NOT predict simulator accuracy" Convergence criteria differ, thus error magnitudes must be

evaluated with user�s topographies on each simulator

Phase-shift error due to grid quantization! Round all mask file coordinates to intended step sizes ! Evaluate (actual � desired) phase-shift! Choose z-step trading off phase error (0-0.5deg)

vs. run-time and simulator accuracy

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Phase – Transmission Error Calculators

Analyze diffraction orders! ProMAX: built-in analysis based on Ferguson[1] method

" Implemented by C. Mack and modified to handle other than 1:1 duty

! TEMPESTp: Export orders and apply Peng[2] equations" Assumes equal line/space. For masks with unequal

line/space, the Peng approach was used to extract phase but not transmission.

[1] R.A. Fergusen, A.K. Wong, T.A. Brunner, and L.W. Leibmann, �Pattern-Dependant Correction of Mask Topography Effects for Alternating Phase-Shifting Masks�, Proc. SPIE 2440, 349-360 (1995)[2] Peng, Song, �Through-Focus Image Balancing of Alternating Phase Shifting Masks�, Proc. SPIE vol. 3873, p.328-336

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Transmission error vs Pitch

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Optimize topography corrections @ 300nm pitch for phase and transmission

Apply these corrections across pitch

Study printability (aerial image, F/E, etc.)

Uncorrected (“geometric”) mask, 248nm 100nm line

Procedure, cont.

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Ph err vs pitch (nm)

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ph, uncorrected, space x=0ph uc100 (p176.4, dt0)ph bias40 (p181, dt0)ph bias40 ARC15 p181ph bias40 ARC25 p181ph SCAA uncorrectedph SCAA ARC15ph SCAA ARC25

Phase Errors Across Pitch

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Trans err vs Pitch

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rr trans, uncorrected, space x=0tr uc100 (p176.4, dt0)tr bias40 (p181, dt0)tr bias40 ARC15 p181tr bias40 ARC25 p181tran SCAA uncorrectedtran SCAA ARC15tran SCAA ARC25

Transmission Errors Across Pitch

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-Conditions for each mask type fixed by optimization at 100/200nm line/space-100nm line masks ranked by overall performance across pitch using normalized power in central diffraction orders as figure of merit.

Correction Type Ph Tr Ph Tr Ph Tr Ph Tr Ph Tr Ph TrSCAA (1) 2.0 0.033 1.1 0.005 -0.2 0.002 0.2 0.008 0.3 0.002 0.1 0.000Asym. Bias (2) -2.3 -0.041 -0.4 -0.004 0.0 0.000 0.2 -0.013 0.6 -0.002 0.9 0.001SCAA (uncorrected) 3.9 0.031 1.2 0.005 -0.2 0.024 0.6 0.018 0.2 0.009 0.1 0.002

AsymBias (4) -0.6 -0.064 0.4 -0.026 0.3 -0.018 0.5 -0.022 0.8 -0.010 0.9 -0.001Additive (uncorrected) -3.8 0.120 -1.7 0.031 -1.4 0.001 -0.2 -0.002 -0.3 0.004 0.1 0.001

Additive (6) -3.6 0.099 -0.2 0.029 0.2 0.001 1.7 0.002 1.4 0.006 1.9 0.005Undercut (7) -2.1 -0.047 -0.2 0.003 0.3 -0.023 -2.7 -0.003 -1.5 0.001 -2.3 0.008Dual-trench + Undercut (8) -8.8 -0.008 -1.2 -0.060 1.2 -0.007 3.0 -0.024 4.3 -0.015 5.8 -0.007

Phase only (9) -4.1 -0.195 0.7 -0.136 -0.3 -0.108 -1.2 -0.068 -0.4 -0.046 -0.5 -0.017None -3.3 -0.205 1.3 -0.147 0.4 -0.117 -0.6 -0.077 0.2 -0.056 0.0 -0.025Dual-trench (11) 12.4 0.037 0.3 -0.007 -2.2 0.025 -5.2 0.000 -5.6 0.005 -7.9 0.000

Pitch 500nm Pitch 1100nmPitch 200nm Pitch 250nm Pitch 300nm Pitch 400nm

KEYGOOD

OKPOOR

Phase: |Effective phase - 180deg|0-.5

0.5-1.5>1.5

Transmission: |(shiftedspace tran - unshifted space tran)|0-.025

.025-.05>.05

Phase and Transmission Results

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Across Pitch RangePhase Trans power sum*

SCAA (1) 2.2 0.033 0.00002Asym. Bias (2) 3.2 0.043 0.00004SCAA (uncorrected) 4.1 0.033 0.00006AsymBias (4) 1.6 0.063 0.00007Additive (uncorrected) 3.9 0.122 0.00014Additive (6) 5.4 0.098 0.00017Undercut (7) 3.0 0.055 0.00017Dual-trench + Undercut (8) 14.6 0.054 0.00051Phase only (9) 4.8 0.177 0.00076None ("geometric") 4.6 0.180 0.00089Dual-trench (11) 20.3 0.043 0.00123

*Power sum = Σ (P0 / 2P1)npitch 1

pitch n

P0 = power in central diffraction orderP1 = power in 1st diffraction order

(2P1 because of two first orders)

! Ranking by diffraction order power:

! Mask Conditions after optimization for 100-200 line-space, λ=248nm1: SCAA, 15nm ARC2: Asym Bias, 181deg phase, 40nm bias3: SCAA, no correction4: Asym Bias, 15nm ARC, 40nm bias5: Additive, uncorrected6: Additive, 182 deg phase

7: Undercut (UC), 100nm UC, 176.4deg phase8: Dual-trench + Undercut, 225nm+20nm 173.8deg phase9: Phase only, 179.7deg phase10: Geometric (no correction)11: Dual-trench, 270nm DT 172.5deg phase

Notes on Mask EMF Results

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AltPSM MEEF Comparison

Masks: SCAA (15nm CrO3 ARC) and Asymmetric Bias (+40nm bias, 181deg phase). Two best masks chosen from earlier table ranking across pitch performance.Input variation: ±40nm mask CD variation for the two best altPSM masksSimulation outline:! Construct ProMAX masks that have wafer line dimensions of

90nm, 100nm and 110nm with 300nm pitch! Run EMF simulations! Export �grayscale� (intensity and phase slice) masks to

PROLITH 7.0 and simulate focus-exposure. Monitor CD, sidewall angle, resist loss and image placement.

! Port FE matrix results to ProDATA and analyze process window using line CD and image placement as responses.

� CD limits 90 to 110nm� Image placement |�5nm to 5nm|

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NILS Comparison of SCAA with 15nm ARC and Asymmetric Bias

NILS through focus for 300nm pitch both mask types are identical.Image CD for SCAA is least sensitive to focus.

Simulation ConditionsPROLITH 7.00.63 NA, 248nm 0.30 sigma

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Asymmetric Bias Process Window MEEF for 300nm Pitch

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F 0.03E 56.02

Group1Doc: Untitled1

Simulation ConditionsPROLITH 7.00.63 NA, 248nm 0.30 sigma304nm UV113 on 20nm CD11+62.5nm AR-5Klarity ProData PW analysis

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90nm 210nm LS

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110nm 190nm LS

%EL=5% Lower LimitP= Image Placement Spec of |-5nm to 5nm|

300nm Pitch

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S CAA 110 190S CAA 100 200S CAA 90 210S CAA 110 190 PS CAA 100 200 PS CAA 90 210 POverlap

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SCAA 100 200SCAA 100 200 POverlapF 0.00

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SCAA 90 210SCAA 90 210 POverlap

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Group5Doc: Untitled1

90nm 210nm LS

100nm 200nm LS

110nm 190nm LS

SCAA Process Window MEEF for 300nm Pitch

300nm Pitch

Simulation ConditionsPROLITH 7.00.63 NA, 248nm 0.30 sigma304nm UV113 on 20nm CD11+62.5nm AR-5Klarity ProData PW analysis

%EL=5% Lower LimitP= Image Placement Spec of |-5nm to 5nm|

MEEF Comparison SummaryFor the two best altPSM mask types, SCAA with 15nm Top ARC and 40nm Asymmetric Bias: ! Similar MEEF of 0.9! Common process window of

0.3µm with 2% Exposure Latitude (%EL) for ±40nm mask CD variation.

! Production process requires less than ±40nm mask CD variation.

For SCAA performance within a single line:! 90nm and 100nm lines have 12 to

14% more DoF than AsymBias! 110nm lines have 2.4% more DoF

than AsymBias110nm line performance is limited by image placement for both masks, but AsymBias is the worst.

Type Line Size 300nm Pitch

ES=100nm CD @ ES=100nm

MEEF EPWCenter DoF w/X% EL Phase Error

Tran Error

SCAA+15nm ARC 90.0 92.0 51.6 1.95 5 +0.25 -0.005

SCAA+15nm ARC 100.0 54.2 98.0 0.88 55.0 2 5 -0.21 0.002

SCAA+15nm ARC 110.0 109.0 59.3 1.67 5 -0.64 0.012

SCAA+15nm ARC Common 55.0 0.3 2

AsymBias 90.0 91.0 52.7 1.73 5 +0.21 -0.013AsymBias 100.0 56.5 97.0 0.90 57.3 1.75 5 -0.02 0.000AsymBias 110.0 109.0 61.5 1.63 5 +0.52 -0.005AsymBias Common 56.0 0.3 2

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Conclusion

SCAA with 15nm ARC performed best across pitch regarding phase and transmission errors at the mask plane, followed closely by the asymmetric biased mask (with 40nm bias each side of shifted space and 181deg design phase shift)All mask types except SCAA required EMF simulation for topography optimizationEMF mask optimization requires systematic simulator setup and gridquantization to bound designed-in errors from desired phase, and to optimize simulator accuracyNILS through focus @ 300nm pitch for best SCAA and biased mask types are identical, whereas Image CD through focus is better for SCAAFor best SCAA and biased masks, each has similar MEEF of 0.9! Common process window of 0.3µm with 2% Exposure Latitude

(2% due to large line change chosen, +/- 10nm at wafer, +/- 40nm at mask)! Even with small MEEF, both mask types require less than ±40nm mask

CD variation for a production process! 110nm line performance is limited by image placement for both masks,

but AsymBias is the worst

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Acknowledgements

Chris Mack, FINLE Technologies, a division of KLA-Tencor, for ProMAX development and consulting

Tom Pistor, Panoramic Technologies for TEMPESTp