The road towards single digit nanometer resolution ...euvlsymposium.lbl.gov/pdf/2015/Oral_Tuesday/Session5_EUV Resist … · Large Scale Facility with Nanotechnology Infrastructure

Elizabeth Buitrago1, O. Yildirim2, R. Fallica1, Andreas Frommhold3, C. Verspaget2, N. Tsugama2,

R. Hoefnagels2, G. Rispens2, M. Meeuwissen2 M. Vockenhuber1 and Y. Ekinci1

1Paul Scherrer Institute, Switzerland 2ASML, Netherlands

3University of Birmingham, UK

The road towards single digit nanometer resolution

patterning in mass production: State-of-the-art EUV

resists platforms

Outline

EUV Interference lithography

XIL-II: EUV-IL tool at PSI

Diffraction grating mask fabrication

EUV resist challenges

State-of-the-art resist platforms:

Positive tone organic chemically amplified resist (CAR)

Negative tone Sn-based resist

Negative tone chemically amplified molecular resist

Conclusions

Slide 2

EUV-IL

XIL-II beamline at Swiss Light Source (SLS):

EUV lithography: 13.5 nm wavelength

Undulator source:

Spatially coherent beam

Temporal coherence: Δλ/λ=4%

Diffractive transmission gratings written

with EBL on S3N4 membranes (~100 nm)

Diffracted beams interfere

Interference pattern printed in resist

Slide 3 m

gp

2sin2

p: period on wafer

g: grating period on mask

m: diffraction order

Advantages of EUV-IL

Stable source: Swiss light synchrotron source (SLS)

Stable interferometer

Infinite depth of focus: Mask-to-wafer (0.3-10 mm)

High resolution:

Theoretical limit = 3.5 nm

Current limit = 7 nm modulation down to 6 nm

Limited by resists and mask writing/quality

Well defined image: pitch independent areal image

Large area for cross-section analysis

Low-cost technique for resist testing

Slide 4

Large Scale Facility with Nanotechnology Infrastructure

Slide 5

Swiss Light Source Laboratory for Micro and Nanotechnology

XIL-II: EUV-IL@SLS

XIL-II: EUV-IL @ PSI

Slide 6

On-site clean room:

Spin-coater, wet-bench, hot-plates, microscope,

developer, optical thickness measurement

In clean room environment with amine filters.

Control

room

Process

room

Exposure

room

Mask Fabrication

Slide 7

direct patterning

two lithography steps

relatively fast, simple process

Silicon nitride membrane, 100 nm

Electron beam lithography HSQ gratings

Masking gratings with PMMA

Cr/Au seed evaporation and liftoff

Au electroplating of photon-stop

Si Si 3 N

4 HSQ PMMA Au

(Fallica et al., MNE 2015) Mask: 11, 12, 13, 14, 16, 18 nm HPs

EUV Chemically Amplified Resist (CAR)

Challenges-Future Resolution (R, HP in nm), line width roughness (LWR, 3σ in nm) and sensitivity

(S, dose in mJ/cm2) cannot be improved simultaneously

RLS trade-off

Higher photon density better LWR high dose (S)

Small Blur better resolution (R) high dose (S)

Larger Blur lower roughness (L) loss of resolution (R)

Low power EUV sources high sensitivity resists required to get high throughput

CARs research and development still dominate, impending need for further R&D and

exploration of state-of-art resist platform alternatives

XIL powerful method in development of EUV resists (CAR and non-CAR)

Different state-of-art EUV resists platforms tested under same process conditions (Mask, UL, resist

thickness, etc., when possible)

Slide 8

Slide 9 Different CAR Resists Compared, HP= 16 nm

HP=16nm-UL1(15nm thk), R1(20nm thk)




29.8mJ/cm2 32.7mJ/cm2 34.5mJ/cm2 36.0mJ/cm2 37.9mJ/cm2 39.6mJ/cm2 41.7mJ/cm2 43.5mJ/cm2 47.8mJ/cm2

36.4mJ/cm2 38.1mJ/cm2 40.0mJ/cm2 41.9mJ/cm2 44.0mJ/cm2 46.1mJ/cm2 48.4mJ/cm2 50.7mJ/cm2

19.4mJ/cm2 20.2mJ/cm2 21.4mJ/cm2 22.3mJ/cm2 23.5mJ/cm2 24.5mJ/cm2 25.8mJ/cm2 26.9mJ/cm2

34.6mJ/cm2 36.2mJ/cm2 38.0mJ/cm2 39.8mJ/cm2 43.8mJ/cm2 46mJ/cm2 50.6mJ/cm2 48.1mJ/cm2

High exposure latitude (EL) for both HP 16 and

18 nm ≥ 24% for all CAR resists

Comparable Z-factors @ 25 nm LRS trade-off

(figure of merit)

UL1R3 has smallest BE = 21mJ/cm2

Name BE (mJ/cm2) EL (%)

LWR (nm) z-factor

UL1R1-25nm 38.4 34.1 6.6 3.4E-08 UL1R1-20nm 43.4 27.4 8.7 6.7E-08 UL1R2-25nm 43.0 24.0 6.4 3.6E-08 UL1R3-25nm 21.0 26.5 6.2 1.6E-08

𝑍 = 𝐵𝐸 × 𝐿𝐸𝑅 2 × 𝐻𝑃 3

Slide 9

CARs 14 and 13 nm HP comparison

Slide 10




HP=13nm-UL1(15nm thnk), R1(25nm thk)

36.6mJ/cm2 38.3mJ/cm2 40.3mJ/cm2 42.1mJ/cm2

37mJ/cm2 38.8mJ/cm2 42.7mJ/cm2 47mJ/cm2

20.7mJ/cm2 21.6mJ/cm2 22.8mJ/cm2

44mJ/cm2

35mJ/cm2 36.9mJ/cm2 38.4mJ/cm2 40.5mJ/cm2

Well resolved patterning down to 13 nm for all CARs.

Small EL ≥ 4.5% @ HP14 for all highly performing CARs

tested and up to 9.7% (UL1R3)

UL1R3 has smallest BE = 22.6mJ/cm2, low LWR (6.7nm)

and high EL down to 14 nm HP (9.7%)

Small EL (3-6%) @ HP13 nm for all except for UL1R3

due to significant pinching, necking and pattern collapse.

UL1R1 @ 20 nm thickness has high EL≥6.5% for

HP=13nm but LWR is high = 11.3 nm

Elevated LWR values also due to bad SEM contrast

extremely thin resist layers

Name HP BE (mJ/cm2) EL (%)

LWR (nm) z-factor

UL1R1-25nm 14 40.1 4.0 7.5 3.1E-08 UL1R1-20nm 14 43.5 8.7 9.6 5.6E-08 UL1R2-25nm 14 44.4 4.5 7.1 3.0E-08

UL1R3-25nm 14 22.6 9.7 6.7 1.4E-08 UL1R1-25nm 13 47.5 3.2 7.9 3.2E-08 UL1R1-20nm 13 58.2 6.5 11.3 8.1E-08

UL1R2-25nm 13 64.5 6.1 8.6 5.2E-08 UL1R3-25nm 13 24.8 0 6.1 1.0E-08

11nm HP, different CARs- Ultimate resolution

Slide 11


HP=11nm-UL1(15nm thk), R2(25nm thk) HP=11nm-UL1(15nm thk), R3(25nm thk)


56.7mJ/cm2 51.2mJ/cm2

40.8mJ/cm2 30.4mJ/cm2

All resists @ 25 nm thickness

are resolved with some

pattern collapse and bridging

down to 11 nm HP.

UL1R1 @ 20 nm thickness

only modulation can be seen

at the dose range tested

Patten collapse still limits

resolution and EL for CARs

Negative tone Chemically Amplified

Molecular Resist: xMT

Slide 12

Resin: Polymer matrix with functional

side-groups, the bulk of the resist

Photo acid generator (PAG):

photoactive compounds that produce

an acid product after interaction with

secondary electrons/photons

Quencher: base neutralizes acid,

improves contrast of the resist (~2%

of PAG)

Solvent: ~90% removed by bake

Crosslinker: to form crosslinks with

the xMT molecule as it cannot do this

by itself. Historically this comes from

previous fullerene-based resists that

are very hard to functionalize with

epoxies

(Frommhold et al., SPIE 2015) Cleaner formulation process, does not require extensive purification

processes to obtain good resists in comparison to Fullerene based resist.

Molecular Resin Crosslinker

PAG Quencher

xMT-0614:

0.2:2:1 xMT:CL06-14:TPS SbF6 PAG + 5% Quencher

Slide 13

PAG Quencher Molecular Resin (xMT) CL06-14

TPS SbF6: triphenyl sulfonium hexafluoroantimonate

xMT-0801:

0.2:2:1 xMT:CL08-01:TPS SbF6 PAG + 5% Quencher

Molecular Resin (xMT) CL08-01 PAG Quencher

(Frommhold et al., SPIE 2015)

2 different crosslinker (CL) molecules tested, same mixing ratio

HP=16nm-Carbon Underlayer(15nm thk)-xMT-0801(25nm thk)

HP=16nm-Carbon Underlayer(15nm thk)-xMT-0614(25nm thk)

Slide 14

Molecular Resists (xMT) compared HP=16 nm



Both xMT materials show well resolved line-spaces down to 16 nm HP.

High exposure latitude (EL) for HP 16 and 18 nm 15% > for both xMT

resists. LWRs as low as 3.1 nm.

xMT-0801 shows low best energy (BE or dose-to-size) ~ 26.6 mJ/cm2

for 16 nm HP. LWRs, overall comparable.

Name BE (mJ/cm2) EL (%) LWR (nm) z-factor

xMT-0614 32.1 17.6 4.3 1.5E-08 xMT-0801 26.6 23.6 5.3 1.2E-08

11nm 12nm HP=14nm

Carbon Underlayer(15nm thk)-xMT-0801(25nm thk)

Carbon Underlayer(15nm thk)-xMT-0614(25nm thk)

Slide 15

Molecular Resists (xMT) compared HP=14 nm and below

xMT-0614 shows well resolved line-spaces down to 12 nm HP with slight

bridging and pattern collapse.

xMT-0801 can resolve down to 12nm HP as well but has prevalent pattern

collapse even at 14 nm HP

xMT-0801 has still lower BE @ 25.9 mJ/cm2 @ 14 nm HP.

No EL <16 nm HP for either due to bridging and pattern collapse

High potential to expand EL down to 11 nm HP features, pattern mitigation

strategy needs to be explored

Great potential for high resolution patterning @ 13 nm HP and below!

13nm 39.5mJ/cm2

11nm 43.2mJ/cm2

12nm 34.9mJ/cm2

30.2mJ/cm2

HP=14nm

13nm 30.9mJ/cm2 41mJ/cm2

36mJ/cm2

Name HP BE (mJ/cm2)

LWR (nm) z-factor

xMT-0614 14 33.4 4.8 1.3E-08 xMT-0801 14 25.9 6.1 1.1E-08 xMT-0614 13 32.5 5.0 8.5E-08 xMT-0801 13 42.7 4.7 1.0E-08 xMT-0614 12 45.2 7.2 2.1E-08

xMT-0801 12 42.9 7.3 2.0E-08

31.6mJ/cm2

Sn-based Resist

Slide 16

Inpria YA

negative tone

organo-oxo molecule

stable after exposure

Sn-based

forms SnO2

high absorption (Sn)

L* = radiation sensitive

ligand

(Fallica et al., MNE 2015)

Sn-based Resist- 16 and 14 nm HP

Slide 17

HP=16nm-YA(25nm thk)


30mJ/cm2 35.6mJ/cm2 38.8mJ/cm2 42.3mJ/cm2 46.1mJ/cm2 54.8mJ/cm2 59.7mJ/cm2 70.9mJ/cm2 77.3mJ/cm2


Two different thicknesses of same resist tested (25, 32 nm).

Super high EL >30% down to 14 nm HP nm for thin resist, EL

decreases to ~13.8% for thick resist @ 14 nm HP

BE increases (54.969 mJ/cm2 @ 16 nm HP) with thickness.

But LWR decreases drastically (2.91.4 nm @ 16 nm HP)with

increasing thickness (as expected).

Thickness HP BE (mJ/cm2) EL (%)

LWR (nm) z-factor

25 nm 16 54.9 31.3 2.9 9.3E-09 32 nm 16 68.9 31.4 1.4 2.8E-09 25 nm 14 67.3 31.8 3.0 8.5E-09 32 nm 14 75.2 13.8 1.7 3.0E-09

Sn-based Resist-ultimate resolution

EL reduced to 11.8% for HP 13 nm (25 nm thickness), super high

for this HP.

12 and 11 nm HPs are well resolved and even small EL ~2% is

possible @ 25 nm thickness for 12 nm HP

Even @ 32 nm thickness 12 and 11 nm HP also look very

promising but pattern collapse limits the EL. Slide 18

HP=12nm-YA(25nm thk) HP=11nm-YA(25nm thk)

HP=12nm-YA(32nm thk) HP=11nm-YA(32nm thk) 74.2mJ/cm2 58.0mJ/cm2 63.2mJ/cm2 68.8mJ/cm2 74.9mJ/cm2

58.1mJ/cm2 63.3mJ/cm2 69.0mJ/cm2 75.2mJ/cm2 45.4mJ/cm2 49.4mJ/cm2 53.9mJ/cm2 58.7mJ/cm2 64.0mJ/cm2 69.7mJ/cm2 76.0mJ/cm2

Thickness HP BE (mJ/cm2) EL (%)

LWR (nm) z-factor

25 nm 13 77.7 11.8 3.3 9.3E-09 32 nm 13 85.0 4.1 1.5 2.0E-09 25 nm 12 86.8 2.4 3.6 9.7E-09

Sn-based resist can be

resolved down to 10 nm HP

with minimum pattern collapse

@ 22 nm thickness.

Thickness reduction is feasible

for this resist due to superior

etch resistance.

Low LWR and high EL at HPs ≤

14 nm makes this resist very

interesting for future high

volume manufacturing needs.

Slide 19

Sn-based Resist-ultimate resolution, 10 nm HP


* Different mask used for this exposure

Z-factor used as global resist performance figure of merit, measure of the RLS trade-off-relationship

Each state-of-the-art resist platform shows different high performance characteristics: BE, EL, LWR, R, z-values comparable for all resists

Slide 20

Z-factors compared for different state-of-art resist platforms @

different HPs

𝑍 = 𝑆𝑒𝑛𝑠𝑖𝑡𝑖𝑣𝑖𝑡𝑦, 𝐵𝐸 × 𝐿𝐸𝑅 2 × 𝐻𝑃 3

Constant Z intersecting smallest Z per HP

Patterning down to 11 nm and 10 nm HP can be done, several resist platforms need to

be further explored for HVM.

EUV photons can do it

EUV-sensitive materials available (CAR and non-CAR)

Tools available for testing

Each state-of-the-art resist platform shows different high performance characteristics, z-

values comparable for all resists

CAR: UL1R3 (25 nm thk) resist demonstrated to be highly performing with high EL > 9.7%, low BE=22.6

mJ/cm2 and low LWRs ~ 6.7 nm down to 14 nm HP.

Sn-based resist (25 nm thk) also high performing with super high EL down to 13 nm ~ 11.8%, and low LWR

~ 3.3 nm

xMT resist with further optimization to widen EL has potential for 14 and 13 nm HP, has low LWR~5nm and

low BE ~ 35 mJ/cm2

Pattern collapse still limiting performance of most resists research ongoing.

Sn-based resist pattern collapse can be mitigated by use of thinner resist due to superior

etch resistance

Conclusions

Slide 21

Acknowledgments

Slide 22

XIL-II team

Members of LMN and SLS

Collaborators

http://www.psi.ch/sls/xil

We thank all of our resist and underlayer suppliers

Thank you for your attention!



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The road towards single digit nanometer resolution ...euvlsymposium.lbl.gov/pdf/2015/Oral_Tuesday/Session5_EUV Resist … · Large Scale Facility with Nanotechnology Infrastructure