Lithography for Silicon-based and Flexible Electronics · 2011-03-12 · Lithography for Silicon-based and Flexible Electronics Christopher K. Ober Materials Science & Engineering

Lithography for Silicon-based and Flexible Electronics

Christopher K. OberMaterials Science & Engineering

Cornell [email protected]

2

Smaller is BetterMoore’s Law after 40 Years

http://www.chips.ibm.com/gallery/p-n2.htmlhttp://www.intel.com/research/silicon/mooreslaw.htm

• Microprocessors with thousands of transistors operating at a few MHz

• Feature sizes of ~ 0.5 µm

• Now few GHz

• Feature sizes of ~ 100 nm

3

International Technology Roadmap for Semiconductors

4

Sowing the Seeds of Nanotechnology

Richard Feynman, “There is plenty of room at the bottom” (1959)

But…….Gutenberg laid the foundation for microlithography when he invented the printing press (~1450)

5

Expose (193 nm or 157 nm) (seconds)

Resist

WaferCoat & Bake

Mask

Positive

Develop (seconds)

Negative

Typical exposure, bake and development times are in seconds!

Strip

(PEB) Post-Exposure Bake (seconds)

Etch (Plasma)

Lithography: the printing press made small

6

Making the Pattern

• Crosslinking• Chain scission• Polarity change

h ν

h ν

h ν

The March to Smaller Dimensions

193 nmImmersion

?

Photoresist

• Photosensitive material used for transferring pattern to substrate

• Has to– Adhere to substrate– Undergo radiation induced solubility change– Possess etch resistance– Be developable in aqueous base (or other solvent)– Disappear when not wanted

9

Limitations of Polymeric Photoresists

Resolution• High molecular weight• Molecular weight distribution

SwellingResidual stress

• Adhesion (collapse)• Distortion

Line width roughness (LWR)

Silicon

resist polymer

http://www.xraylith.wisc.edu

Topics

• High resolution DUV lithography• Without chemical amplification• 193 nm immersion• 157 nm lithography

• E-beam lithography• EUV Lithography• Thick film lithography• Future directions in lithography

• Imprint lithography• Ink jet printing

11

Resists without Chemical Amplification

• Established technology– Mostly used as electron-beam resists– Was original basis of DUV resists

• High resolution (no acid diffusion problems)• Sub 30 nm feature sizes possible• Problem: Low sensitivity! How to improve?

– Currently low sensitivities are traded for high resolution

12

Electron Beam Lithography

• Characterized by expensive systems and long write times– Typically used for mask making or MEMS devices

e-

13

PMMA

+

O

E-Beam

• Excellent resolution (<30 nm) + Contrast

• Low sensitivity (800µc/cm2 @ 100kV)

• How to improve sensitivity?

-copolymerize with MAA for 4x increase in sensitivity

E-beam Technology Group, Stanford Nanofabrication Facility

14

E-Beam Sensitivity of PMMA Analogues

Copolymer Sensitivity (15 kV, µC/Cm2)

PMMA 40

X = Me, Y = COOH 35

X = Me, Y = CN 12

X = Me, Y = Me 14

X = Cl, Y = COOMe 12

X = CN, Y = H 12

• Stability of Radical intermediates seems most important factor

• From ‘Introduction to Microlithography’ p. 202

15

Styrene Monomers

insensitive neg. tone resist

insensitive pos. tone resist

Highly sensitive Negative tone

Sensitivity

‘Introduction to Microlithography’, p 207

E-beam Resists

17

Improving the Sensitivity of Chain Scission Resists

• Electron withdrawing groups or copolymerization with appropriate Chromophore

PMMA-phenyl isopropyl ketone (PIPK)

(ZEP Photoresist) resolution of 20nm possible

•Note: Both examples result in more stable radical intermediates

C.Pittman et al J.Electrochem soc., 1981, 1759,

K. Sugita et al, Polymer J., 1993, 25, 1059

18

IBM Terpolymer Resist• High sensitivity (7 µC/Cm2 at 15 kV)• Positive-tone resist based on chain scission

Moreau, W, et al. J. Vac. Sci. Technol. 1979, 16(6) 1989

19

Poly (1-Butene Sulphone)

• Very sensitive, but poor dry etch resistance!

+

• Again, favorable decomposition route. Note release of neutral species.

R-SO2-R [RSO2R]+ RSO2+ + R R+ + SO2

20

Overcoming poor etch resistance…

• Use poly(2-methylpentene sulfone) as a sensitizer with Novolac resin:

• Bowdon M. J., et al, J. Electrochem. Soc. 1981, 128, 1304

• Variation: Ito, H., et al, J. Electrochem. Soc. 1988, 135(6), 1504

21

• Silicon-containing resistsOvercoming poor etch resistance…

Fox12™ (hydrogen silsesquioxane) PDMS-PVMS

• Crosslink upon e-beam exposure• Very low sensitivities, but high resolution (~20 nm)

22

Epoxy Resists• Negative tone rendered insoluble by radiation induced ring opening and

X-Linking, classic example: COP (Bell Labs)

Thompson, L.F. et al, Polym. Eng. Sci, 1974, (14) 7, 529

23

Epoxy Resists – Molecular glass

• Calix[4]arene derivative, negative-tone by epoxy ring opening

Ruderisch, A.; Sailer, H.; Schurig, V.; Kern, D. P., Microelectron. Eng. 2003, (67-68) 292.

• Other Derivatives:

24

Olefin-co-CO Copolymers

+Propylene-CO

Ethylene-CO

• Propylene-CO much more sensitive: Decomposition more favorable

S.G. Bond et al, Polymer, 1994, 35, 451

25

Photosensitive polyimidesiloxane

Jeng, S.; Xu, M.; Liu, P. L.; Kwok, H. S.; Lee, C. J. MRS Symposium Proceedings 1990, (167), 111.

• Crosslinks upon UV exposure, dose of 100mJ/cm2

26

Key Concepts

• To Improve Sensitivity:

(1) Build in bonds capable of cleavage (2) Ensure stability of intermediates(3) Release of neutral species, i.e. SO2

CNF NanoCourses

CORNELL NANOSCALE FACILTY • CORNELL NANOSCALE FACILITY • CORNELL NANOSCALE FACILITY • CORNELL NANOSCALE FACILITY

E-Beam Resists and Processing

Positive resists PMMA Toray EBR-9 PBS ZEP Photoresists as e-beam resists

Negative resists COP Shipley SAL NEB-31

Multilayer systems Low/high molecular weight PMMA PMMA/copolymer Trilayer systems

CNF NanoCourses


Poly(methyl methacrylate) (PMMA)

The most popular e-beam resist Extremely high-resolution Easy handling Excellent film characteristics Wide process latitude Usually dissolved in a solvent (e.g. anisole) Exposure causes scission of the polymer chains Solvent developer dissolves exposed (lighter molecular weight)

resist

CNF NanoCourses


PMMA Characteristics

Positive acting Several viscosities available, allowing a wide range of resist

thickness Not sensitive to white light Developer mixtures can be adjusted to control contrast and

profile Appropriate processing results in undercut profile for liftoff Poor dry etch resistance No shelf life or film life issues

CNF NanoCourses


Spin-Speed Characteristics for PMMA,

Thicker films

CNF NanoCourses


P(MMA-MAA) Copolymer Resist

Higher sensitivity than PMMA Can be exposed at a lower dose Faster Less contrast.

Most useful in Bi-level resists with PMMA, to produce undercut profiles useful in liftoff processing

Characteristics Positive acting Several viscosities available, allowing a wide range of resist thickness Not sensitive to white light Developer mixtures can be adjusted to control contrast and profile Poor dry etch resistance No shelf life or film life issues

32

UV Lithography

• Only optical lithography can provide the information output needed for high volume production

• Industry loves this and will keep pushing it as long as it can go

33

Azo resists

34

Azo Absorbance

35

Azo Patterning

UV Stepper Tool (248/193 nm)

• Canon FPA-5500iZ step-and-repeat i-line stepper for 300 mm is a mix-and-match companion for the company's 300 mm scanners, the FPA-5000ES3 (KrF) and the FPA-5000AS2 (ArF). The tool can be easily converted to or from 200 mm wafer size and can be used for patterning less-critical IC layers. The unit includes the same third-generation platform as the company's 300 mm scanners.

DNQ Resists

Introduction to Microlithography, 2nd Ed., L. Thompson, C.G. Willons, M. J. Bowden, eds., ACS Books, Washington, 1994.

Interactions of Photoactive Molecule with Matrix

10

100

1000

10,000

R0

Rp

hν

Dissolution Rate(≈/s)

+

+

DNQ / Novolak Photoresists

*Courtesy George Barclay (Shipley)

OH

Limited Light Sources

R = k1λ/NA

Changing Wavelengths

248 nm

248 nm365 nm

193 nm

157 nm

EUV (13 nm)

X-ray

Resists with Chemical Amplification

Resist Components• Polymer• Solvent• Photoacid Generator (PAG)• Additives (e.g. DI,plasticizer)

Positive Chemically Amplified Photoresist Chemistry

0.12µm

0.40µm

PAG

hv H+


Photoacid Generator (PAG) Classes

Non-Ionic PAGsHalogenated Compounds:

Sulfonate Esters/Sulfones:

Ionic PAGsOnium Salts:


Positive Photoresist Technology

Differential in Aqueous Base Solubility - Deprotection Chemistry

Dis

solu

tion

Rat

e

40 A/sec

30,000 A/sec

+ H+


130 °C

Development Trends in MicrolithographyArchitectures


45

Photoresists for ArF (193 nm) Lithography

• The current state-of-the-art in the microelectronics industry.

• Capable of producing features as small as 65 nm.

Nikon Precision, Inc.

46

Resist Transparency at 193 nm

• Aromatic groups are highly absorbing at 193 nm wavelength– Phenolic groups used for 248 nm lithography cannot

be used here• Methacrylate groups are transparent

– Low plasma etch resistance• Alicyclic groups are transparent

– Plasma etch resistance similar to aromatics

Kunz RR, Allen RD, Hinsberg WD, Wallraff GM.. Proc. SPIE 1993; 1925: 167-175. Takechi S, Kaimoto Y, Nozaki K, Abe N. J. Photopolym. Sci. Technol. 1992; 5: 439-445

47

First 193 nm Photoresist

• Excellent transparency• Excellent solubility• Poor etch resistance

Poly(t-butyl methacrylate - methacrylic acid)

Kunz RR, Allen RD, Hinsberg WD, Wallraff GM.. Proc. SPIE 1993; 1925: 167-175.

48

Alicyclic Structures Improve Etch Resistance

• Norbornene group adds etch resistance• Maleic anhydride group adds solubility• Carboxylic acid leads to film swelling during

development

Cycloolefin-maleic anhydride (COMA) resist

Allen RD, Wallraff GM, DiPietro RA, Kunz RR. J. Photopolym. Sci. Technol. 1994; 7: 507-516.Allen RD, et al. J. Photopolym. Sci. Technol. 1995; 8: 623-636.

49

Swelling?

• Prior to dissolution, exposed film swells as the aqueous developer enters– Large dissolution/swelling front

• Ultimate resolution is mechanically hampered due to swelling

• Swelling can be controlled by adjusting compositions

Varanasi PR, et al. Proc. SPIE 2005; 5753 , 131.

50

Hexafluoroisopropanol Groups

• Similar pKa to that of phenolic groups– Good dissolution

• Fluorinated groups have high transparency at 193 nm.• Less prone to cause swelling compared to carboxylic

acid.

Ito H, Seehof N, Sato R, Nakayama T, Ueda M. Synthesis and evaluation of alicyclic backbone polymers for 193 nm lithography. in ACS Symp Series 706, Micro- and nano-patterining polymers Ito H, Reichmanis E, Nalamasu O, Ueno T. ed. American Chemical Society, 1998; chap 16, 208-223.

51

Current examples

• Adamantyl groups further add etch resistance• Lactone groups increase solubility• Long aliphatic chains further reduce swelling

Varanasi PR, et al. Proc. SPIE 2005; 5753 , 131.

52

Silsesquioxanes

• Transparent at 193 nm• Silicon drastically increase etch resistance• Standard resist chemistries added for solubility

Ito, H, et al. Proc. SPIE 2005; 5753 , 109.

R=

53

Increasing NA: Immersion ArF Lithography

• Placing a fluid with a higher refractive index than air (n=1) increases depth of focus and ultimate resolution– Water: n=1.45 @ 193 nm

ASML. Brewer Science ARC Symposium, Albany, Oct 28, 2004

54

Immersion Lithography

• Issues:– Film swelling due to water– Water must be ultra-pure,

free of bubbles– Leaching of resist

components into water must be controlled

55

Immersion Lithography

• Solutions:– Transparent topcoat over resist to reduce

interaction between resist and water– Engineer resist platforms to increase

hydrophobicity– Use PAGs and additives that do not strongly

segregate to the surface.

Houlihan, F, et al. Proc. SPIE 2005; 5753 , 78.

248 to 193 to 157 Dilemma

248 nm Resists– Aromatic, phenolic structures– Acids as base soluble groups

193 nm Resists– No aromatics - cycloaliphatic structures for etch resistance

157 nm Resists– No aromatics, no acids– Fluoropolymers and activated alcohols for base solubility

57

Absorbance of Polymers at 157 nm

Kunz, R.R; Bloomstein, T. M; ,Hardy, D. E; Goodman, R. B; Downs, D.K; Curtin, J.E, Proc SPIE 3678:13 (1999)

“Fluoropolymers and Polysilsesquioxanes”

Challenges for NGL Resists for 157 nm Imaging

Requirements Targets Strategies

Transparency A < 2 µm–1 Hydrofluorocarbon>30% fluorination

Acidic group forbase solubility

Etch resistance

Imaging group

pKa ~ 10 Fluorocarbinols

Comparable toNovolac system

Alicyclicstructures

Cleavable by PAG* Alkoxy alkyl ethers

*PAG: Photochemical acid generator

59

Structural Elements for CA 157 nm Resist Design

Back Bone (Transparency)

Etch Resistance

Developer Selectivity

Protecting Group

Hydorofluorocarbon

Alicylic with Electron

attracting group

Fluoro Carbinol

Alkoxy ethers

Patterson, Kyle; Somervell, Mark; Willson, C. Grant. The challenges in materials design for 157nm photoresists, Solid State Technology (2000), 43(3), 41

Design

Sub Elements Example

60

157 nm Resist Based on CO/NBHFA Vinyl Addition Polymer

VUV Spectra of NBHFA Polymers

70/30 blend of vinyl addition

copolymer with CO Polymeric DI

VUV Spectra of CO Polymers

CO norbornene terpolymer

performance

Reduced OD

Higher contrast with Dissolution Inhibitor

First Commercial Resist [PNBHFA with 20 mol % t-BOC + CO DI – Clariant]

Absorption reduced by acetal Protecting and geminal CF3 group

Hung, R.J;Tran, H.V;Trinque, B.C; Chiba, T;Yamada, S; Sanders, D.P; Connor, E. F; Grubbs, R.H; Klopp, J; Fréchet, J.M.J; Thomas, B.H; Shafer, G.J; DesMarteau, D.D; Conley, W; Willson, C.G Proc SPIE, 4345, 385 (2001)

Trinque, B. C; Osborn, B. P; Chambers, C.R; Hsieh, Y-T; Corry, S; Chiba, T; Hung, R. J; Tran, H,V; Zimmerman, P; Miller, D; Conley, W; Willson C G Proc SPIE 4690, 58 (2002)

61

Tetrafluoroethylene (TFE) based 157 nm Resist

VUV absorbance of spectra of fluoropolymer with TFE in the background with those without TFE

Cross-section SEMs of the 100 nm lines of a resist containing TFE as a co monomer. Resist thickness was 157 nm, A = 2.3 µm-1and the OD = 0.36

Crawford, M. K; Feiring, A. E; Feldman, J; French, R.H; Periyasamy, M; Schadt, F.L III;, Smalley, R.J; Zumsteg, F.C; Kunz, R.R; Rao, V; Liao, L; Holl, S. M Proc SPIE 4345, 428,2001

Lower absorptionLower hydrophilicityLower dry etch resistantSpecial Condition for polymerization

62

All Acrylate and Acrylate/NBHFA Copolymers for 157 nm

Poly(methyl 2-trifluoromethylacrylate) [PMTFMA] an e-beam resistPMTFMA Absorption at 157 nm 3.1/µmReplacement of CH3 to CF3 Reduces the OD to three to four timesFacile copolymerization with NBHFACopolymer of acrylate/NBHFA reduces the absorption of polymer to OD of 2.6 -2.7/µmLiphophilic and insoluble in TMAH – Maximum NBHFA is 40 mol %Blending of NBHFA increases the hydrophilicity and reduces the OD to 2.0/µm

Matsuzawa, N; N; Mori ,S;Yano, E; Okazaki, S; Ishitani, A; Dixon, D. A Proc SPIE 3999, 375, 2000Ito, H;Truong, H.D; Okazaki, M; Miller, D.C; Fender, N; Breyta, G; Brock, P.J; Wallraff, G.M; Larson, C.E; Allen, R.D Proc

SPIE 4690,18, 2002

VUV-VASE Spectra

140 160 180 200 220 240 260 280 300

0.0

0.5

1.0

1.5

2.0

2.5

3.0A

bsor

banc

e, µ

m-1

Wavelength, nm

2.03 µm–1

@ 157 nm

– After exposure, the resist was soluble in 0.262 N TMAH Y. C. Bae*, K. Douki, T. Yu, J. Dai, D. Schmaljohann, H. Koerner, C. K. Ober*, W. Conley, “Tailoring Transparency of Imageable Fluoropolymers at 157 nm by Incorporation of Hexafluoroisopropyl Alcohol to Photoresist Backbones”, Chem Mater., (2002), 14(3), 1306-1313.

157 nm Resist Performance

0

0.2

0.4

0.6

0.8

1

1 10 100Dose(mJ/cm2)

Thi

ckne

ss

THPMA=40mol%

THPMA=30mol%

THPMA=20mol%

Version 4

– Clearing dose: ~16 mJ/cm2

– Better contrast with more THPMA– Higher dose with more THPMA: requires more PAG

PAB: 115 oC/ 90 sec; PEB: 90 oC / 90 secPAG: 1 wt% TPSNf; 0.26 N TMAH for 60 sec

A: 2.4 µm-1

A: 1.6 µm-1

<ISSUE> • Top rounding (too absorbing @ 157 nm)

<ISSUE>• obtained mostly homopolymer of methacrylate

• Only latent image @ 248nm• Low Tg• Poor dissolution contrast

<ISSUES>

157nm Resist Strategies

Vohra, V.; Douki, K.; Kwark, Y.; Liu, X.; CKO; Bae, Y. C.; Conley, W.; Miller, D.; Zimmerman, P. Highly transparent resist platforms for 157-nm microlithography: an update. Proceedings of SPIE-The International Society for Optical Engineering (2002), 4690 84-93.

66

157 nm Lithography

130 nm 1:5 L/S

80 nm L/S

R ~ 5 nmEUV

A=2.5µm-1

Y. C. Bae, C. K. Ober et al.“Tailoring Transparency of Imageable Fluoropolymers at 157 nm by Incorporation of Hexafluoroisopropyl Alcohol to Photoresist Backbones”, Chem Mater., (2002), 14(3), 1306-1313.

hν

PAG

A Matter of Scale

Carbon Nanotube

Photoresist (150 nm)

Intel 4004 Patterned atoms

HumanHair

Red blood cells

Dimensions (nm)

Virus

NGL Lithography

• Extreme UV (EUV)– 13 nm radiation

• Ion projection lithography (IPL)– Less likely than a couple years ago

• SCALPEL– Projection e-beam/high res. E-beam resists

• X-ray– Same issues as EUV/need synchrotron

• Step and Flash – Limited production/lower fidelity

69

0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

3,000,000

3,500,000

4,000,000

Absorbance at 13.5 nm

• Resist absorption at 13.5 nm depends only on chemical composition and density of the material

Pho

toab

sorp

tion

cros

s-se

ctio

n (c

m2/

mol

)

EUV Lithography

• Challenges for this new technology include:

• Manufacturing of optics including multi-layer coatings with atomic precision

• Developing powerful sources• Manufacturing of defect-free reflection masks• Controlling contamination (molecular and particulate)• Cost of ownership

EUV Stepper

Eric J. Lerner, “Next-Generation Lithography”, The Industrial Physicist 18 June 1999

72

Requirements for EUV Resists

Year 2009

Resolution – Gate (nm) 15

Resolution – ½ pitch (nm) 45

LWR - 3σ (nm) 1.5

Sensitivity (mJ/cm2) 2-5

Absorbance (µm-1) Low

Depth of Focus (µm) > 0.2

Outgassing No outgassing

Collapse No collapse

Intel targets for insertion of EUV tools into manufacturing in 2009

Cao, Heidi, et al., Proceeding of SPIE 2003, 5039, 484.

73

Resists For EUV Lithography

• Challenges: resists need to have:

High Sensitivity (Weak sources) High resolution (for small feature sizes) Low LER Minimal outgassing (damages optics)

• Most conventional resists are patternable at EUV wavelengths, But…

None so far meet all of these requirements

74

Is Absorbance Important in EUVL?

Reducing absorbance increases resolution and wall angle.

18

20

22

24

26

28

30

32

1 2 3 4 5Absorbance ( µm-1)

CD

(nm

)80

81

82

83

84

85

86

87

88

89

90

Ang

le (°

)Smaller absorbance1 5 (µm-1)

Distance (µm)

Res

ist H

eigh

t (µ

m)

Beta tool (NA=0.25, sigma=0.5) Resist thk = 60 nm, Dose = 2.95 mJ/cm2

0.231 0.238 0.245 0.253 0.260 0.268

0.000

0.012

0.024

0.036

0.048

0.060

Cao, Heidi, et al., Proceeding of SPIE 2003, 5039, 484.

75

Novel systems…

• Mass persistent protecting group to minimize outgassing

• EUV lithography pattern profiles of positive resist poly(HOST-co-MBAMA): (a) 100 nm line and space (1:1) elbow pattern; (b)–(e) 100–50 nm line (pitch 180 nm) pattern.

• Gonsalves K, et al, Microelectronic engineering 2005 77, 27-35

76

Experimental Data for λEUV

βxλ

π=µ

β+δ=

θ−+θ

θ−−θ=

4 )( Absorbance

- 1 index Refractive

Rs

in

nn

2

22

22

cossincossin

0

1

2

3

4

5

6

0 2 4 6µexperimental

µ cal

cula

ted

Grazing Angle Incidence

PMMA

Ref

lect

ance

Angle (deg)%The measured absorbance values match well with the calculated ones.

Si wafer coated with polymer

detectorsource

θ θ

l

Difference (D) = (µcalc-µexp)/µcalc × 100 (%)* Density not determined.

77

Effect of Si and O Components

calculation experiment

78

Design Strategy

Transparency Polarity Acid sensitivity

Styrene-Based Positive Tone EUV Resists

79

5% TPS triflate115°C, 60s PAB115°C, 60s PEB60s development in 0.263N TMAH w/surfactant

P-A

50 nm L/S 32.5 nm L/S

EUV Exposure Results

Structures for Single Layer Silicon-containing EUV

Resists

Negative-tone

N-A

N-B

Positive-tone

P-B

P-A

P-A

Positive-tone EUV Resists -- Exposure Results

5% TPS triflate115°C, 60s PAB115°C, 60s PEB60s development in 0.263N TMAH w/surfactant

T= 0.652, 125nm

34 nm 56 nm

Dai, Junyan; Ober, Christopher K.; Kim, Sang-Ouk; Nealey, Paul F.; Golovkina, Victoria; Shin, Jangho; Wang, Lin; Cerrina, Franco. Synthesis and evaluation of novel organoelement resists for EUV lithography. Proceedings of SPIE (2003), 5039 1164-1172.

82

Silicon Etch Resistance

0

0.167

0.333

0.500

0.667

0.833

1.000

APEX P-A P-B

O2 etchingCF4 etchingCHF3/O2 etching

P-A P-B

Rel

ativ

e E

tch

Rat

e

83

248 nm and EUV Exposure

Pitch = 150 nm

A10 = 1.53 µm-1 A10 = 1.42 µm-110 : 27 : 63 30 : 20 : 50

Pitch = 100 nm

• High resolution and good transparency, but LER issues

84

Silicon in the Main Chain

Polysilanes

Polysiloxanes - polysilsesquioxanes

Polysilazanes - polysilsesquiazanes

Polycarbosilanes

Multiple bonds on Si center may minimize outgassing problem.

85

Modified Polysilanes

8 : 2A10 = 1.10 µm-1 A10 = 1.2 µm-1

Much better resist performance

86

Outgassing at 13.4 nm

87

Molecular Size

• Molecular glasses can possess substantially smaller size

• Many of same features as polymer• More uniform distribution of resist

additives

Poly(hydroxy styrene), DPn = 50

Molecular glass resist components

88

E-beam Molecular Glass Resists

• High dosage (12 ~ 14 mC/cm2 @ 50kV)

Positive-tone resists:

Negative-tone resists:

Kadota, T.; Yoshiiwa, M.; Kageyama, H.; Wakaya, F.; Gamo, K.; Shirota, Y. Proceedings of SPIE 2002, 4345, 891-899

89

Calixarene Based Molecular Glass Resists

• Micron size patterns obtained with DUV exposures

Positive-tone resists:

OH

ORO

R

O R

OR

OR O

R

OR

OR

HO

HO

HO

OH

OH

OH

OH

RO

ROH3C

RO OR

CH3

OR

ORCH3

ORRO

H3C

OCOCH3

CH3

OCOCH3OCOCH3

OCOCH3

CH3

OCOCH3

CH3CH3

H3COCO

CH3CH3

Calix[8]-arene, R=Ac, TsC4-R, R=H, t-BOC

Hexaacetate p-methylCalix[6]-areneCalix[4]-resorcinarene

HO

HOH3C

HO OH

CH3

OH

OHCH3

OHHO

H3C

Negative-tone resists:

• 7 nm pattern obtained by Ebeam• Low sensitivity (mC/cm2)

Haba, O.,M. Ueda et al. Chem. Mater.1999, 11, 427-432

Nakayama, T.; Ueda M. J. Mater. Chem.1999. 9(3), 697-702

Kwon, Y., M. Ueda et al. J. Mater. Chem. 2002. 12, 53-57

Fujita, J. et al. Appl. Phys. Lett. 1996, 68(9), 1297-1299

90

pg

CoreAcid Acid

Ac

id A

cid

PG PG

PG

PG

%High glass transition temperature

%High etch resistance

%Solubility switch%High glass transition

temperature%High etch resistance

%Acidity%H-bonding with resist

components%Solubility, adhesion

Protecting group

Design of Molecular Glass Resists

91

Molecular Glass Design

High Tg• Rigid molecular structure

• Strong attractive forces• H-bonding

Amorphous• Low tendency toward

crystallization

• Asymmetric structure Etch resistance

High C/H ratio

EUV Less oxygen

78% tBoc, Tg: 67 °C

66% tBoc, Tg: 58 °C

74% tBoc, Tg: 25 °C

75% tBoc, Tg: 52 °C

No Tg observed before decomposition

92

Positive-tone Molecular Glass Resist - 248 nm Images

4.2 mJ/cm2 (250nm L/S)28.6 mJ/cm2 (250nm L/S)

65 mJ/cm2 (350nm L/S) 30 mJ/cm2 (350nm L/S)

93

Negative-tone Molecular Glass Resist

TMMGU Crosslinker

Glasses

Photoacid Generator

94

Negative-tone Molecular Glass Resist - Chemistry

Insoluble cross-linked oligomerSoluble monomer

unexposed exposed

expose

95

Negative-tone Molecular Glass Resist - 248 nm Images

3.6mJ/cm2 3.6mJ/cm2

55.7 mJ/cm2 19.3 mJ/cm2

96

E-beam Molecular Glass Resist

15 wt% TMMGU5 wt% TPS NonaflatePAB: 115ºC, 60sPEB: 115ºC, 60sDevelopment: 0.026N TMAH, 10s

60µC/cm2 @100kV

Dose range 60 – 240 µC/cm2 @100kV60 nm pattern image at 180µC/cm2 @100kV

97

Line Width Roughness - Preliminary Results

3sigma = 6.14 nm 4.35 nm/pixel

3sigma = 5.12 nm4.08 nm/pixel

100nm dense lines

100nm isolated line

Calculation program courtesy Professor Francesco Cerrina research group at University of Wisconsin-Madison

98

0

0.5

1.0

1.5

2.0

2.5

3.0

PHS

MG4 tBOC

MG4 THP

SPIRO N

eg

MG4 Neg

MG10 N

eg

Yu, T.; Ching, P.; Ober, C. K. Proceedings of SPIE 2001, 4345, 945-948

Nitride Etch Resistance

99

Positive-tone Molecular Glass Resist – EUV Images

10.0mJ/cm2 Bright Field

5 wt% TPS Nonaflate0.14 wt% TOAPAB: 115ºC, 60sPEB: 115ºC, 60sDevelopment: 0.026N TMAH, 30s

Images obtained at Lawrence Berkeley National Laboratories by EUV microexposure tool

40 nm is < 1/1000th the size of a human hair

100

Summary• The ability to make nm-scale patterned

structures continues to advance• Shorter wavelength optical lithography now

rivals the best e-beam imaging• Alternative methods are on the horizon (e.g.

step-and-flash, self-assembly)• Eventually these methods will be routine and

impact all areas of science and technology

Patterned Surfaces

101

Dry Film Photoresists

• polyester support sheet for the photosensitive material

• layer of photoactive monomer mixed with polymeric binder and other materials

• polyolefin cover sheet withich prevents photoresist from sticking or “blocking” when it is wound on a roll

• exposures can take several minutes

Dry Film Initiator Structure

102

N

N

N

N

Cl Cl

N

N

Cl

light

2

Ia

Ia +H3CH2C N

R

R

N

N

Cl

+ H3CHC N

R

R

II IIa

Dry Film Dye Formation

103

Ia + CH NR

R

NR

R

N

R

R

III

C NR

R

NR

R

NR

R

- electronC N

R

R

NR

R

NR

R

Pattern Formation

104

IIa + CH2C

CH2

H2C

H2CO O

O

CH3

OO

O

Polymer Network

IIa + IV +

IV

*HC

H2C

HC

HC *

OO

OH OH

V

nPolymerized matrix

Circuitization

105

106

System Supplier

Cleaning/Wet Process Kraemer KoatingWet Stripper/Developer Hollmuller Siegmund

Large High Vacuum Coater* CHAIn-line Defect Inspection* ECDPrecision Lithography* AzoresPrecision Wet Coat & Bake Frontier IndustrialOLED Evaporation Source* KJL

Small High Vacuum Coater* TBDManual Inspection Table TBD

Defined Systems

*USDC supported

107

Scrub/Rinse

Poly Tank

SSTank

RewindUnwind

Air KnifePoly Tank

• Kraemer Koating, 2001

• 6” to 14” width

• Designed for cleaning and/or wet processing

• Recirculation w/cascading possible

• 0.2 to 10 FPM

• 0.5 PLI to 1.6 PLI

Cleaning/Wet Processing: Capability

108

• Hollmuller Siegmund (MacDermid) 1993

• Up to 15” width

• Designed for Develop & Strip

• Heated tanks (three process and two rinse)

• Stripper: Stainless Steel (DuPont Riston II S-1100X)

• Developer: Polypropylene (DuPont Riston II D-2000)

• Air Knife

• Currently rebuilding web handling

Wet Stripper/Developer: Capability

109

AzoresCorp, 2006

• Based on proven FPD stepper

• 8” width, can handle up to 24” with new chucks

• g-line (436 nm)

• 4 µm L/S

• 230 to 760 mm/min

• 400 ppm distortion compensation

• Requires hole-punch pattern for pre- alignment:

Precision Lithography: Capability

Web handlers in test

110

Other Printing Methods

A

C

E

B

Transducer Ink reservoir

SubstrateNozzle

F

Silicone pad

SubstrateCliche InkD

Inkjet Methods

111

Thermal Inkjet Printing Piezoelectric Inkjet Printing

112

Ink Jet Printing

500 nm

Ink dropletSurface

energypattern

AB

C

113

Drop Spreading

100 µmsource

drain

gate

channel

A

B

C

114

Wetting Control

50 µm

PEDOT/surfactant

PEDOT

PEDOT

Surfactant molecules

A

B

C

115

Ink Jet Circuits

B

C

B

A

116

Printed Designs

117

Soft Lithography

• Umbrella term for ‘unconventional lithography’• Includes molding, embossing and printing.• Recent reviews:

Gates, B.D. et al, Chem. Rev. 2005, 105, 1171

Gates, B.D. et al, Annu. Rev. Mater. Res. 2004, 34, 339

Resnick, D. J. et al, Materials Today, 2005, 8, 34

• Included in ITRS roadmap (2010)

Comparison of Imprint Lithographies

Christie R. K. Marrian and Donald M. Tennant, “Nanofabrication”, J. Vac. Sci. Technol. A 21(5) S207 2003

Step and Flash Process

T. Bailey, B. J. Choi, M. Colburn, M. Meissl, S. Shaya, J. G. Ekerdt, S. V. Sreenivasan, and C. G. Willson, “Step and flash imprint lithography: Template surface treatment and defect analysis”, J. Vac. Sci. Technol. B 3572 18 2000

Sub-100 nm Features

121

Soft Stamp (i.e. PDMS)

Microcontact Printing (µCP)

• Uses a soft stamp to apply ‘ink’ to a substrate

Soft Stamp (i.e. PDMS)

Substrate, typically a metal Transfer ‘Ink’

Wet with ‘Ink’ i.e. thiol.

Press Stamp

Etch • Ink binds by Chemisorption of Physisorbtion

• Forms self assembled monolayer (SAM) at point of contact with substrate

122

Fabrication of Stamps for Soft Lithography

Hard Substrate

Photoresist

Expose + Develop

Etch

Elastomeric pre-polymer

Elastomeric polymer

Cure/HeatPeel off

• Hard substrates include quartz, SiO2, Cr. • Soft stamps made from PDMS, PFPE

Use as Hard Mold or…. Use to make soft stamp

123

Pros and Cons of µCP

• Can generate large patterns of SAM’s (>cm2) across curved surfaces.

(Delamarche, E. et al. Langmuir 2003, 19, 8749)

• Good for fictionalization of surfaces for different applications, i.e. biomaterials

(Brock, A. et al, Langmuir 2003, 19, 1611)

• Resolution depends on binding of ink to substrate. Can’t be considered a universal method.

124

Nanoimprint lithography (NIL)

• Uses rigid mold (i.e. silicon)

Ridged Mold

Polymer Film

Substrate

Ridged Mold

Substrate

Heat > Tg and Imprint

Ridged Mold Ridged Mold

Substrate

Cool < Tg

Release Mold

Etch, etc.

• High Temp., High Pressure• High viscosity medium• Can be difficult to fill all voids in the mold and obtain uniform patterns

125

Applications of NIL

• Extension of process used to make DVD’s, holograms etc.

SEM images of structures patterned by nanoimprint: (a) 10-nm diameter metal dots with a periodicity of 40 nm, and (b) Fresnel zone plates with a 125-nm minimum line width. (c) SEM

image of features patterned by SAMIM. Gates, B.D. et al, Annu. Rev. Mater. Res. 2004, 34, 339.

126

• Density of patterning layer…

Easiest… Easy… Very Difficult!

“Base layer”

Solution? Use a low viscosity patterning layer

(Slide Courtesy of G. Willson)

Problems with NIL

127

Step-and-flash Imprint Lithography (SFIL)

Dispense

template etch barrier

transfer layer

Expose

Separate

release treatment

Imprint

Breakthrough Etch

Transfer Etch

Residual layer

• Etch barrier: UV Curable monomer (low viscosity)

• Avoids density problems with NIL


UV Cure

Halogen RI Etch

O2 RI Etch

128

Composition of the Etch Barrier

O2 Etch Resistance

X-Linker (Lowers Viscosity)

UV Free-Radical Initiator

129

• Resolution theoretically limited by template

• Pattern fidelity not so good for small feature sizes-still some interaction between template and etch barrier


30 nm 20 nm 20 nm

Resolution of SFIL

130

Step-and-Flash Imprint Lithography (SFIL)

• Low cost, potential for step-and-repeat process

• Formation of multilayer structures possible

SEM images showing cross sections of multi-tiered structures on a template fabricated with alternating layers of ITO and PECVD oxide.

Johnson et al., Microelectron. Eng. 67-68 (2003), 67, 221

131

Soft Lithography: Summary

• Low cost compared to Photolithography

• Potential for Step-and-repeat processes

• SFIL looks most promising technique

• Pattern fidelity issues must be overcome!

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Lithography for Silicon-based and Flexible Electronics · 2011-03-12 · Lithography for Silicon-based and Flexible Electronics Christopher K. Ober Materials Science & Engineering