solid immersion and evanescent wave lithography … · evanescent wave lithography at numerical...

16
Center for Nanolithography Research Solid Immersion and Evanescent Wave Lithography at Numerical Apertures > 1.60 Bruce Smith Y. Fan, J. Zhou, L. Zavyalova, M. Slocum, J. Park, A. Bourov, E. Piscani, N. Lafferty, A. Estroff Rochester Institute of Technology Center for Nanolithography Research

Upload: doanhuong

Post on 30-Aug-2018

233 views

Category:

Documents


0 download

TRANSCRIPT

Center for Nanolithography Research

Solid Immersion andEvanescent Wave Lithographyat Numerical Apertures > 1.60

Bruce SmithY. Fan, J. Zhou, L. Zavyalova, M. Slocum, J. Park, A. Bourov,

E. Piscani, N. Lafferty, A. Estroff

Rochester Institute of TechnologyCenter for Nanolithography Research

Center for Nanolithography Research

Outline

The imaging limits of materials

Pushing the limits of immersion lithography

The solid immersion lens

Solid immersion lithography (SIL)

Evanescent wave lithography (EWL)

Imaging 26nm at 1.85NA

Center for Nanolithography Research

“glass”

media

photoresist

substrate

“glass”

media

photoresist

substrate

Material and Optical Limitations

NA = ni sin θ

1. Sin θ increases slowly at large angles (sin 68°=0.93)

2. Hyper-NA will be forced upon material refractive index

3. Resolution will become a function of the lowest index (fluid, optics, photoresist).

nmn62to

n52

(0.93)nm)0.30)(193nto(0.25

sinθnλkhp

iiii

1min ===

Center for Nanolithography Research

Technology Limits in Media

Fused silica (n=1.56) Sapphire (n=1.92)

TIR @θc = sin-1(nL/nH)

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90

Angle (degrees)

Ref

lect

ance

32°

TM

Air (1.00)H20 (1.44)

HIF (1.54)SIL (1.70)

67° 58°49°

TE

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90

Angle (degrees)

Ref

lect

ance

32°

TM

Air (1.00)H20 (1.44)

HIF (1.54)

67° 58°49°

TE

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90

Angle (degrees)

Ref

lect

ance

TM

Air (1.00) H20 (1.44)HIF (1.54)

SIL (1.56)

90°84°68°

TE

40°

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90

Angle (degrees)

Ref

lect

ance

TM

Air (1.00) H20 (1.44)HIF (1.54)

90°84°68°

TE

40°

TIR from Snells’ Law:

θc = sin-1(nL/nH)

Center for Nanolithography Research

Numerical Aperture1.3 1.4 1.5 1.6 1.7 1.8 1.9 2

Half-Pitch (nm) k1=0.25 37 34 32 30 28 27 25 24k1=0.30 45 44 39 36 34 32 30 29

Angle in media Water (1.44) 65° 76°HIF (1.55) 57° 65° 75°HIF2 (1.65) 52° 58° 65° 76°Photoresist (1.70) 50° 55° 62° 70°HI PR (1.85) 45° 49° 54° 60° 67° 77°Fused silica (1.54) 58° 65° 77°Sapphire (1.92) 43° 47° 52° 56° 62° 70°

Technology Limits in Media

TIR

Center for Nanolithography Research

Impact of Angle in Photoresist Simple Approximations

0

0.2

0.4

0.6

0.8

1

1.2

0 20 40 60 80

Angle in resist (degrees)

Unp

olar

ized

mod

ulat

ion

0

1

2

3

4

5

6

7

Abs

orpt

ion

scal

ing

0

5

10

15

20

25

30

35

0 20 40 60 80Angle in resist (degrees)

DO

F sc

alin

g ⎥⎦⎤

⎢⎣⎡

θsin1

2⎥⎦⎤

⎢⎣⎡

θcos 1

AbsorptionModulation

Oblique absorption requires low k photoresistParaxial DOF scales with 1/sin2(θ)Angles above 30° (0.85 NA) require attentionOblique reflection becomes an issue > 30°

Polarization and absorption Depth of focus

0.85

NA

1.20

NA

0.85

NA

1.20

NA

Center for Nanolithography Research

A Solid Immersion Lens

znnsin

n/

upper

lowerupper

e)z(A⎟⎟⎟⎟

⎜⎜⎜⎜

+⎥⎥

⎢⎢

⎟⎟⎠

⎞⎜⎜⎝

⎛−−

=αθ

λπ

21222

- A high index solid immersion lens is placed in close proximityto an image plane

- “Dry imaging for NA values > 1.0- Used in optical storage applications

- Energy coupled into the thin film decays exponentially:

nupper = lensnlower = airz = gap

Center for Nanolithography Research

Solid Immersion LithographySapphire SIL Breadboard

Sapphire Properties:- Hexagonal, single-crystalline Al2O3- n = 1.92, birefringence ~8x10-3

- Equilateral prism at 60° is 1.67NA- Designed for NA 1.05~1.92- MgF2 is ideal AR layer

Polarized ArF beam

Grating mask

Zero-order block

Turning mirrors

Sapphire prism

prism

Challenges:- Gap and gap control- Birefringence- CAR resist diffusion length limit- Resist/BARC process optimization

cylinder

Center for Nanolithography Research

Laser Detector Laser

Optical Coupling in the Prism

(a) Baseline (no wafer). (b) Reflection (with wafer).

(a) Before pressure is applied. (b) After pressure is applied.

Detector

Center for Nanolithography Research

NA=1.66

0

0.2

0.4

0.6

0.8

1

0 10 20 30 40 50Air gap thickness (nm)

Ref

lect

ance

TheoreticalMeasurement

Immersion solid (sapphire), N0=1.92 Air gap, N1=1.00, d1=0~50 nm

Resist, N2=1.71-0.399i, d2=78 nm BARC, N2=1.70-0.1i, 92 nm

Substrate Nsub=0.87-2.76i

Resist assembly

Estimation of Gap Thickness- Reflectance measurement

used to estimate gap thickness.

- Gap controllable from 0-50nm- 12nm air gap utilized.

Center for Nanolithography Research

1.42NA, 34nm 1.60NA, 30nm 1.66NA, 29nm

Solid Immersion Lithography at the Resist Limit

ILSim simulations

Center for Nanolithography Research

Beyond the Resist LimitEvanescent Wave Coupling

nuppersinθ = NAmax

nlowersinθ

NA = nisinθHomogeneous

propagation

Evanescent region

higher n

θc

nlower- low

Homogeneous propagation

Evanescent region

nupper- hi

thin film

znnsin

n22/12

upper

lower2upper

e)z(A⎟⎟⎟⎟

⎜⎜⎜⎜

α+⎥⎥⎥

⎢⎢⎢

⎟⎟⎠

⎞⎜⎜⎝

⎛−θ

λ

π−

=

Energy coupled into the thin film decays exponentially:

Center for Nanolithography Research

1.85NA, 26nm

Evanescent Wave LithographyBeyond the Resist Limit - 26nm hp at 1.85NA

NA (1.85) has been pushed higher than the index of the resist (1.70).Image pattern depth of <10 nm.Sets the stage for new material

development toward 25nm.Potential with TSI and hard-

mask imaging layers.

Center for Nanolithography Research

Gap Requirements / TolerancesAssume 50% intensity loss across the image – no loss in modulation

1% gap ∆ results in ~0.5-1% intensity ∆ at 1.70NA – dose control issue

znnsin

n22/12

upper

lower2upper

e)z(A⎟⎟⎟⎟

⎜⎜⎜⎜

α+⎥⎥⎥

⎢⎢⎢

⎟⎟⎠

⎞⎜⎜⎝

⎛−θ

λ

π−

=

010

203040

506070

8090

1.65 1.70 1.75 1.80 1.85 1.90

Numerical ApertureG

ap (n

m) f

or 5

0% in

tens

ity

10

20

30

40

50

60

70

80

1.0 1.1 1.2 1.3 1.4 1.5 1.6

Gap Index

Gap

(nm

) for

50%

inte

nsity

28nm hp at 64° in sapphire HIF2 gap for 0.25k1

Water

HIF2 28nm hp

27nm hp

Center for Nanolithography Research

Implications of SIL andEvanescent Wave Lithography

1. SIL / EWL is useful for determining the ultimate limits of optical lithography in the 25nm regime.

2. NA possible beyond the fluid index.

3. Higher index photoresists may not be necessary if top-surface imaging (TSI) can be employed.

4. SIL may be feasible if small fluid gaps can be maintained.

Center for Nanolithography Research

Numerical Aperture1.3 1.4 1.5 1.6 1.7 1.8 1.9 2

Half-Pitch (nm) k1=0.25 37 34 32 30 28 27 25 24k1=0.30 45 44 39 36 34 32 30 29

Angle in media Water (1.44) 65° 76°HIF (1.55) 57° 65° 75°HIF2 (1.65) 52° 58° 65° 76°Photoresist (1.70) 50° 55° 62° 70°HI PR (1.85) 45° 49° 54° 60° 67° 77°Fused silica (1.54) 58° 65° 77°Sapphire (1.92) 43° 47° 52° 56° 62° 70°

Can be achieved with immersion lithography

May be possible with SIL / EWL

Not likely

Technology Limits in Media

Acknowledgements

SRC, DARPA/AFRL, Sematech, ASML, Photronics, TOK, JSR, Rohm and Haas, Brewer, NYSTAR, Corning Tropel