non-traditional molecular resist designs: cationic...

2009 International Symposium on Extreme Ultraviolet Lithography

1

Non-Traditional Molecular Resist Designs: Cationic Polymerization

1

Todd R. Younkin, Wang Yueh, Steve PutnaIntel Corporation

Richard Lawson1, Laren M. Tolbert 2, Clifford L. Henderson1*1School of Chemical & Biomolecular Engineering

2 School of Chemistry and BiochemistryGeorgia Institute of Technology

* Corresponding Author: [email protected]



2Non-Traditional Molecular Resist Designs• Single Component Molecular Resists

– Show improved LER, reasonable resolution, but unexpectedly poor sensitivity

O

O

OCH3

S OO

ON

O

O

O

O

• Negative Tone Molecular Resists Based on Cationic Polymerization– Showed excellent resolution, sensitivity, and LER under e-beam

• Single component MR are still under investigation, but negative tone has shown better performance so far – more cycles of learning in negative tone

O

O

OOO

O

O

O

O

O

O

O

O

O

OO

OO

2-Ep 3-Ep 4-Ep


3

• Potential advantages of cationic polymerization CARs – Superior mechanical strength – high MW cross-linked film – Superior environmental stability – highly stable cationic chain propagation

controls conversion– Intrinsic diffusion control – active cation directly attached to growing

chain/network– No outgassing of resist – zero mass loss process

3Cationic Polymerization as an Imaging Mechanism

H+ -MXnO

R+

kHO

R

H-MXn

O

R+

kI

HOO

R-MXn

O

R+

kPn HOO

RO

R -MXn

n

R

R

Negative Tone Molecular Resists can meet sensitivity and resolution requirements for 22 nm patterning and below.

• The imaging mechanism is different from conventional CARs – instead of a diffusing/reacting photoacid, the photoacid protonates an epoxide which forms an active cation that carries out the reaction


4Pattern Collapse Behavior

• Special patterns were developed to precisely determine the stress that lines undergo during development and rinse

• The superior mechanical strength of 4-Ep leads allows it to withstand higher stresses than conventional resist polymers

⎟⎟⎠

⎞⎜⎜⎝

⎛−⎟

⎠⎞

⎜⎝⎛=

21

2 11cos6SSW

Hc θγσ

0

2

4

6

8

10

12

14

16

18

20

40 60 80 100Feature Width (nm)

Crit

ical

Stre

ss (M

Pa)

ESCAP4-Ep

O

O

O

O

O

O

O

O


5Environmental StabilityDirect Base Addition Effect on 4-Ep

• Even high base loadings (1:1 PAG:base) have little effect on epoxide cross-linking

N

TOA

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 5 10 15 20Dose (mJ/cm2)

NR

T

0 TOA1:2.33 TOA:PAG1:1.00 TOA:PAG

DUV Contrast PEB 60 oC

• Conventional CARs regenerate the acid after each deprotection reaction

• Acid is rapidly converted to initiated active cation in epoxides that is not reactive to base


6Last Year’s Status of Epoxide Resist Work• Investigation of MR core and degree of functionality effects was conducted• All compounds show excellent resolution, sensitivity, and LER.• Higher functionality compounds show better sensitivity

O

O

OOO

O

O

O

O

O

O

O

O

O

OO

OO

2-Ep 3-Ep 4-Ep

25 nm 1:1

100 nm

35 nm 1:1

60 nm

35 nm 1:1

60 nm

75 µC/cm2 (100keV)t = 50 nm

LER = 2.8 nm

50 µC/cm2t = 110 nm

LER = 2.3 nm

50 µC/cm2t = 70 nm

LER = 2.3 nm

6

50 nm 1:1

60 nm


7Benchmarking Against A Commercial System

• 4-Ep shows superior resolution and LER to SU-8

• Swelling appears to be main failure for SU-8 – periodic failure direct indication

• Higher cross-link density and rigidity of network in 4-Ep and other epoxide resists as comapred to SU-8 results in more favorable imaging

55 nm 1:2

O

O

O

O

O

O

O

O

O

O

O

O

O

O

O

O

O

O

O

O

O

O

O

O

SU-8

4-Ep

35 nm 1:1

60 nm

35 nm 1:1

60 nm

50 nm 1:270 nm 1:1


88Contrast and E0 Behavior for 1st Gen. Epoxides

• E-beam: γ = 1.2 (4-Ep), 1.3 (3-Ep), 1.5 (2-Ep)• EUV: γ = 2.3 (4-Ep) vs. 1.3 (2-Ep)• Bigger potential problem is E0 is virtually zero

– Any tool flare or noise can have significant effect on patterning

5 mol% TPS-SbF6, PEB = 90oC 1 min., MIBK dev.

100 keV e-beam EUV

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 20 40 60 80Dose (µC/cm2)

NR

T

4-Ep3-Ep2-Ep

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 2 4 6 8 10Dose (µC/cm2)

NR

T

4-Ep2-Ep


9Intrinsic Capability vs. Realistic Imaging:E-beam vs. EUV

• Esize @ PSI = 8 mJ/cm2 for PEB = 90oC (Dose-to-Mask = 24.7 mJ/cm2 March 08 at PSI)

• LER (3σ) = 4.9 nm at PSI (larger than e-beam)• Imaging performance degraded further under ALS exposure• Relatively low contrast and low E0 in 1st Gen. epoxide resists

degrade imaging performance in low NILS and high flare imaging

E-beam, 35 nm 1:1 PSI EUV 32 nm 1:1 ALS EUV 32 nm 2:1

O

O

O

O

O

O

O

O4-Ep


10

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 5 10 15 20Dose (mJ/cm2)

NR

T

0 NH4Tf1:3 NH4Tf:PAG1:1 NH4Tf:PAG

Contrast and E0 Control:Finding Additives for Polymerization Control

• What will act to quench a cationic polymerization? A strong nucleophile such as a triflate anion can act as a chain termination agent.

DUV Contrast PEB 60oC

-34

Added to 4-Ep

Strong nucleophiles can limit polymerization but reduce contrast.


11

• Addition of strong nucleophile shows significant effect in quenching • Only want to terminate polymerization outside the exposed region• A photo-decomposable nucleophile would satisfy these requirements

• TPS-Tf added to 4-Ep formulation• Triflic acid acts like chain transfer agent – regenerating the initial

photoacid

Photo-Decomposable Nucleophiles (PDN)

exposed

unexposedPDN


12Photo-Decomposable Nucleophile – TPS-Tf• Has benefits of nucleophilic quencher with less drawbacks• Contrast improved (γ0 = 0.49, γ1:4 = 1.14, γ1:2 = 1.13) • Most importantly – shift E0 away from zero• 4-Ep.0, 4-Ep.25, 4-Ep.50 = % loading of TPS-Tf/TPS-SbF6

DUV Contrast PEB 90oC

Sb-F F

FFF

FS+ SO

O

-O CF3S+

TPS-TfTPS-SbF6

0

0.2

0.4

0.6

0.8

1

0 5 10 15 20Dose (mJ/cm2)

NR

T

4-Ep.04-Ep.254-Ep.50


1313PDN Enhances EUV Performance of Epoxides

• Modified resist formulation, 1:2 TPS-Tf:TPS-SbF6• Esize = 15 mJ/cm2 (Dose-to-Mask = 45 mJ/cm2 July 08)• LER (3σ) = 4.0 nm for 50 nm lines, 4.5 nm for 25 nm lines• 22 nm lines show modulation but limited by pattern collapse

50 nm 30 nm 25 nm 22 nm

No PDN Best


14EUV Resist Testing: Mask & Tool EffectsALS Mask Effect on Patterning at 45 nm

• 4-Ep.50 10 mJ/cm2 PEB 60 °C, 60 sec.• Mask has large effect on pattern quality and pattern sizing• Dark vertical cleave shows best resolution and patterning

Bright Resolution

Dark Resolution

Pseudo Dark Resolution

Dark Vertical Cleave


154-Ep.50 on Dark Vertical Cleave (DVC)45 nm 1:1

30 nm1:1 1:1.5 1:2

25 nm1:1 1:1.5 1:2

• Resolution down to 25 nm 1:2 – limited either due to bridging defects or pattern collapse

• 70 nm thick resists – ~ 10.75 mJ/cm2

25 nm1:1


164-Ep.50 Rotated Dipole DVC – 12 mJ/cm2

• Resolution down to 25 nm 1:2, 25 nm 1:1 collapse• Under ALS, resolution can still be achieved, but LER is

significantly worse.

45 nm 1:1 25 nm 1:2


17Next Generation Designs – Base Developed• New designs allow for greatly improved contrast and aqueous

base development

Epoxides

Molecular Glass Core

Base Solubilizing Group

• The most important result toward improving EUV performance of these systems – shift of E0 away from zero.

0

0.2

0.4

0.6

0.8

1

0 10 20 30 40 50Dose (mJ/cm2)

NR

TPEB 60°CPEB 90°C

DUV Developed in 0.26N TMAH


18New Design Cross-Linking Mechanism

• An additional catalytic cycle (reaction pathway) opens when carboxylic acids are added to the epoxide compounds.

• Rates: Reaction B > Reaction A >> Equilibrium C• Equilibrium C may slow the overall reaction and could potentially

act like an acid trap at low doses.


1919Exploring New Functional Groups

• Appears capable of achieving resolution to 15 nm and below

• Currently limited by pattern collapse or e-beam tool limitations

• LER (3σ) = 3.0 nm

OO

O O

O O

35 nm 1:1 25 nm 1:2 20 nm 1:2 15 nm 1:3


2020Summary• Epoxide functionalized molecular resists show promise to satisfy

patterning requirements for 22 nm node EUV and below– Resolution: 25 nm 1:1 and below (EUV and e-beam)– Sensitivity: 8-15 mJ/cm2 (EUV); 30-75 µC/cm2 (e-beam on ultra-low

backscatter substrates)– LER (3σ): 4.0-4.8 (EUV); 2.3-3.0 (e-beam)

• Several new polymerization control agents were developed that allow for even higher resolution and contrast for all similar systems

• New designs allow development in both aqueous base and organic solvent with improved contrast

4-Ep PSI25 nm 1:115 mJ/cm2LWR: 5-6 nmO

O

O

O

O

O

O

O


212121

• Harun Solak, Vaida Auzelyte, and Anja Weber at PSI for EUV exposures

• Patrick Naulleau, Brian Hoef, Lorie Mae Baclea-An, Simi George, and Gideon Jones at ALS for EUV exposures

Acknowledgements

EUV 25 nm 1:1


Additional Slides


23Effect of PAG Loading on 4-Ep

• Increasing the PAG loading only acts to shift the dose-to-size, but provides no improvement to LER

5 mol % 10 mol % 15 mol %

8.3 mJ/cm2LER: 4.9 nm



non-traditional molecular resist designs: cationic...

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