factors affecting the “non-cleanables measurement of...

Factors affecting the “non-cleanables”

measurement of resist outgas testing:

interpreting the null results

1

S. Hill, N. S. Faradzhev, B. Berg, T. B. Lucatorto

NIST, Gaithersburg, MD, 20899 USA

M. Barclay, H. Fairbrother

Johns Hopkins University, Baltimore, MD 21218, USA

D. Alvarado, M. Upadhyaya, Y. Kandel, G. Denbeaux

CNSE, State University of New York, Albany 12203,USA

Special Thanks to Tonmoy Chakraborti , SEMATECH

EUVL Symposium, Toyama, Oct. 10, 2013

ASML Resist-Outgas Testing Protocol at NIST

(1) Determine E0 (2) Co-expose witness sample & resist-

coated 200 mm wafer to E0 in 1 hr.

(3) Measure C-thickness with

spectroscopic ellipsometry

and scale to 300 mm wafer (4) Clean C with atomic H

<3nm

(5)

Measure amount

of residual non-C

{S, P, F, I, Cl, …}

with XPS.

2

• Referred to as “non-cleanables,” yet no resist has ever failed due to non-C

residuals.

• Typically XPS does not detect atomic concentrations significantly above

background levels of S.

• F is rarely observed (in contamination spot) despite being common resist

component.

• Resist developers may avoid elements like iodine with high PAG quantum

efficiency due to potential contamination risk.

• Systematic study of actual contamination threat posed by non-C outgas

species is needed.


EUV/e-beam exposure of polymer films

Spin coat

Ru-MLM substrate

1) Spin coat <10 nm film of polymer onto Ru-cap MLM substrate & characterize

2) Perform EUV/e-beam exposures with varying dose

3) Characterize changes with spectroscopic ellipsometry (SE) and XPS

4) Subject to atomic-H (AH)

5) Characterize with SE and XPS

SE & XPS

EUV AH cleaning

SE & XPS Analyze native

film SE & XPS

1 2 3 4 5

3

S-containing: (C10H18S)n

Poly(3-hexylthiophene)

P3HT or

Repeat to determine cleaning rate

F-containing: (C2H2F2)n

Polyvinylidene fluoride

PVDF


EUV interaction with P3HT and PVDF

4

XPS

• ~ 40% of S is rapidly desorbed by EUV (<10 J/mm2)

• ~60% of S is resistant to desorption by highest doses

• No evidence of C desorption

P3HT: (C10H18S)n

WS

outgas

test dose

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S is partially desorbed by EUV


Consistent with x-ray-induced desorption of F but not S during XPS measurements

(observed by EIDEC and confirmed in collaboration with NIST)

5

F is strongly desorbed by EUV S is partially desorbed by EUV

PVDF: (C2H2F2)n

XPS

P3HT: (C10H18S)n

WS

outgas

test dose

• ~50% of F is rapidly desorbed by low doses

• F continues to desorb with increasing dose


• ~ 40% of S is rapidly desorbed by EUV (<10 J/mm2)

• ~60% of S is resistant to desorption by highest doses


EUV interaction with P3HT and PVDF

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outgas

test dose


Compare EUV & e-beam desorption of F from PVDF

• Dose response from correlation of XPS maps and dose distributions across exposure spots

• Similar trends in EUV and e-beam data suggest two-step desorption process

• Electrons appear to desorb F ~100x more efficiently than EUV

• Does this mean that e-beam-based outgas tests are inherently insensitive to F contamination?

6

Slower second reaction:

Cross sec. ~ 5×10-20 cm2

Fast initial reaction:


Slower second reaction:


Fast initial reaction:


PVDF exposed to EUV PVDF exposed to 2keV e-beam

Johns Hopkins Univ. NIST


7

XPS

EUV interaction with PVDF

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PVDF: (C2H2F2)n

F:C before AH cleaning


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• The presence of F significantly slows overall cleaning rate of PVDF

• Areas exposed to high EUV doses have lower F:C ratios and hence clean fastest

Atomic-H cleaning of PVDF: C removal

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XPS

PVDF: (C2H2F2)n


EUV-deposited C


9

Atomic-H cleaning of PVDF: F removal

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XPS

PVDF: (C2H2F2)n



• F is removed by AH at very slow rate

• The amount of F detected in XPS portion of outgas test could be artificially lowered by

Excessively long AH cleaning times (cleaning until all C is gone)

Witness sample intensity much higher than that expected on lowest-intensity NXE optic

10

• AH removed all P3HT after first short cleaning interval

• AH cleaning rate for P3HT (S:C~10%) is at least as fast as typical EUV-deposited C.

• S is removed at least as quickly as C and does not affect C cleaning rate

AH cleaning of P3HT (S-containing polymer)

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XPS

PVDF: (C2H2F2)n


P3HT lower bound

EUV-deposited C


[email protected]

Studying the effectiveness of cleaning

• After over 100 customer samples, none have failed the non-

cleanables specification

• We did more in depth measurements of one sample – it started

with 15 nm of contamination growth

Measured XPS of the contamination spot PRIOR to cleaning

Partially cleaned multiple times with XPS after each clean cycle to

measure the composition within the contamination, during cleaning, and

after cleaning

XPS XPS XPS XPS

Partial clean Partial clean Partial clean

ellipsometry ellipsometry ellipsometry ellipsometry

Atomic hydrogen cleaning

EUVL Symposium, Toyama, Oct. 10, 2013 11

[email protected]

Composition between cleaning steps

• Primarily carbon contamination spot, after cleaning primarily ruthenium substrate

• Oxygen is present in the contamination, but at a higher level on the ruthenium substrate

carbon ruthenium

oxygen

thickness

0

2

4

6

8

10

12

14

16

18

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25

Thic

kne

ss (

nm

)

Ato

mic

co

nce

ntr

atio

n (

%)

Cleaning time (hours)

Nitrogen, sulfur, silicon


[email protected]

Composition between cleaning steps

• Sulfur is present in both the contamination spot and the final cleaned ruthenium surface

• Sulfur in contamination is elemental, in/on ruthenium surface is sulfur oxide

thickness

0

2

4

6

8

10

12

14

16

18

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 5 10 15 20 25

Thic

kne

ss (

nm

)

Ato

mic

co

nce

ntr

atio

n (

%)

Cleaning time (hours)

silicon

nitrogen

sulfur

5 - 130929A_CG150_CG151_CG103.104.spe: 130929A_CG150_CG151_CG103 PHI

2013 Oct 1 Al mono 64.9 W 200.0 µ 45.0° 224.00 eV 1.8187e+004 max 6.73 min

S2p/9/1

1551601651701751.73

1.74

1.75

1.76

1.77

1.78

1.79

1.8

1.81

1.82x 10

4 5 - 130929A_CG150_CG151_CG103.104.spe

Binding Energy (eV)

c/s

1 - CG103 & CG106.102.spe: CG103 & CG106 PHI

2013 Apr 15 Al mono 44.6 W 200.0 µ 45.0° 224.00 eV 3.8033e+003 max 6.73 min

S2p/3/1

1551601651701752200

2400

2600

2800

3000

3200

3400

3600

3800

40001 - CG103 & CG106.102.spe

Binding Energy (eV)

c/s

Sulfur in

contamination

primarily

elemental

Sulfur on

witness plate

in partially

oxidized state


Summary

14

• S-containing polymers and outgas contamination appear to clean at rate

similar to pure EUV-deposited C.

• Atomic-H cleaning rate of C is significantly slowed by presence of F.

• F is rarely observed in outgas testing because it is efficiently desorbed by

EUV & electrons not because it is efficiently cleaned by atomic H.

• Electrons desorb F (from polymer PVDF) ~100x more efficiently than EUV

• Is e-beam outgas testing inherently insensitive to F contamination?

• NIST and EIDEC systems use EUV on witness sample and have reported small

amounts of F (< 1 atomic %) before AH cleaning.

• Has F ever been seen in any e-beam test?


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