An Overview of Soft-Lithographies for Materials Patterning and Device

Fabrication

Will Childs, Keon Lee, Svetlana Mitrovski, Lindsay Elliott, John Rogers, and Ralph Nuzzo

University of Illinois at Urbana-ChampaignFrederick Seitz Materials Research Laboratory

Department of ChemistryDepartment of Materials Science and Engineering

http://www-306.ibm.com/chips/gallery/www.just2good.co.uk/ cpuSilicon.htm

The “Si Standard” for Materials Patterning: Photolithography

WaferWith Photoresist

Pattern Copied

Lens

Photomask

Light

p M O S n a n o - t r a n s i s t o rp M O S n a n o - t r a n s i s t o r

Intel: 30 nm

Nanoelectronics: Materials and Manufacturing Challenges

Bell past and future(?)

Photolithography: It always wins!

Immersion Lithography: 65 nm using 193 nm ArF(limit ~35 nm)

{Resolution ~ (Wavelength/NA); NA = n x sinθ}

Photoresists: As Good as Organic Chemistry Gets!There are so many choices (some of my favorites).

Amplified Resists SU-8: the Monster of MEMS(many variants)

Nanofabrication: Molecular Imprints

Step and Flash

Soft Lithography: Materials Patterning via Physical Contact/Mass Transfer

-[Si(CH3)2-O]-n

The Core Material of Soft Lithography

Near Field Phase-shift Photolithography

Rogers, J. A.; Paul, K. E.; Jackman, R. J., Whitesides, G. M. Appl. Phys. Lett. 1997, 70, 2658.

head group

carbon chainsulfur

2-3

nm

The “Au Standard” for Materials Assembly: Self-Assembled Monolayers (SAMs)

1 cm

Image of Gold Surface Patterned withHydrophobic and Hydrophilic SAMs

XX X

X

xx

xx

SSS

SS

S

S

S

STM Image of a SAM

1 cm

Image of Gold Surface Patterned withHydrophobic and Hydrophilic SAMs

1 cm1 cm

Image of Gold Surface Patterned withHydrophobic and Hydrophilic SAMs

Self-Assembled Monolayers (SAMs): Organic Materials Surface Chemistry

Self-Assembling Monolayers (SAMs)

Laibinis, Paul E.; Whitesides,G. M.; et al. J. Am. Chem. Soc. 1991, 113, 152.

Self-Assembled Monolayers (SAMs): an Ink

Xia, Y.; Whitesides, G. M. Angew. Chem., Int. Ed. 1998, 37, 550. Michel, B.; Bernard, A., et al. IBM J. Res. & Dev. 2001, 45, 697.

Soft Lithography: Masters

Patterning TechniquesE-Beam FIB (Focused Ion Beam)

Photolithography Micromachining

Holography SPM lithography

Master

Cast/MoldPDMS

Stamp

Pattern

Transparent

Low Thermal Expansion

Chemically Inert

Reusable for patterning

Best Resolution: 2-10 nm

Poly(dimethylsiloxane)

Environmentally Safe

Silanized

Rapid Prototyping

Microcontact Printing

a-c: Silver; e: Gold; f: copper

a+b: rolling stamp

g+h: metal as etch mask for silicon

Xia, Y.; Whitesides, G. M. Ann. Rev. Mater. Sci 1998, 28, 153.

Microcontact Printing: Patterned SAMs are Used to Define Fabrication Level in Au via Wet Etching

Rogers, J. A. et. al. Proc. Nat. Acad. Sci. USA 2001, 98, 4835-4840.

Dodabalapur, A.et.al. Appl. Phys. Lett. 1998, 73, 142-144.

Electronic Paper

20µm

spherical curvature

PZT Fresnel Lens Patterned using Microcontact Printing, a Soft-Lithographic Patterning Method

PDMS Stamp

Patterned OTS SAM on Quartz: Lift-off Patterning on Si and Glass

• Sol-gel Ceramics•Evaporated Metals

(poor as an etch resist)

Microcontact Printing

a: polyurethane (PU)b: CuSO4c: Cu CVD on Sid: LiNbO3 CVDon Si/SiO2

Xia, Y.; Whitesides, G. M. Ann. Rev. Mater. Sci 1998, 28, 153.

≤ 50 nm Resolutionof Etched Gold

Michel, B.; Bernard, A., et al. IBM J. Res. & Dev. 2001, 45, 697.

MicroMolding in Capillaries (MiMIC)

a: PU on Sib: polyanilinec: ZrO2

d; polystryene colloidse+f: free standing PU

Xia, Y.; Whitesides, G. M. Ann. Rev. Mater. Sci 1998, 28, 153.

Jeon, N. L.; Hu, J.; Whitesides, G.M.; Erhardt, M.K.; Nuzzo, R.G. Adv. Mater. 1998, 10, 1466.

200 µm

Challenges: Registration, Resists

Ex: MOSFETs

Vd

-16 -14 -12 -10 -8 -6 -4 -2 0

Id

-0.0008

-0.0007

-0.0006

-0.0005

-0.0004

-0.0003

-0.0002

-0.0001

Vg= -4 VoltsVg= -5 VoltsVg= -6 VoltsVg= -7 Volts

Solvent Assisted MicroMolding (SAMiM)

photoresist ona: SiO2b: polystrenec: ABS

Xia, Y.; Whitesides, G. M. Ann. Rev. Mater. Sci 1998, 28, 153.

Duffy, D. C.; Jackman, R. J., et al. Adv. Mater. 1999, 11, 546.

Continuous MembranePattern

Add or Remove Layer

Dry Lift-Off

Spin-Cast PDMS Membrane

Jackman, et al.; Langmuir 1999, 15, 2973.

Elastic Membrane Patterning

electroluminescent materials

plasma etch resist

Replica Molding (ReM)

PDMS master

PU mold

Xia, Y.; Whitesides, G. M. Ann. Rev. Mater. Sci 1998, 28, 153.

Cohesive Transfer Lithography

PDMS molding

UVO treatment

Heat or UV curing (Closed)

Physical removal (Open)

• UVO bonded PDMS features can be torn from stamp• Works best for small feature sizes ( < 5 µm)• PDMS resists transferred from a non-composite stamp are thin ( < 100 nM)• Effective RIE/Liftoff resists—aSi, metals, etc.• Limit: composite stamps embedding a release level are exceptionally hard to master for feature sizes below 1 µm—segments detach from transfer pad during molding process.

MicroTransfer Molding (µTM)

a+b: PU c+d: epoxy e+f: solgelXia, Y.; Whitesides, G. M. Ann. Rev. Mater. Sci 1998, 28, 153.

Quake, S.R., et al. Science 2002, 298, 580.

Integrated Microfludics

Integrated Microfluidcs

Loading Separation

Mixing Purging

BR

AW

BWAR

High Voltage A

High Voltage B

1. 100 W Hg Arc Lamp2. Aperture Stop3. Field Stop4. Dichroic Cube Assembly5. PDMS Device6. 80:20 Beam Splitter7. Tube Camera8. R-376 PMT

S-20

(R-3

76)

Olympus AX-70

1

23

4

5

67

8

Fabrication and Detection using PDMS

place desired pattern onphotoresist & irradiatewith UV light (365nm)

spin coat STR 1075photoresist on Si wafer

wash off exposed resistwith basic developer

cure PDMS elastomer onSi/photoresist master

peel off PDMS

seal with second PDMSplanar substrate

Typical dimensions from channel intersection to reservoir are (BR) 8 mm, (AR) 8 mm, (AW) 8 mm, (BW) 60 mm. Channel cross sections ~15 µm (height) x 90 µm (width).

Schematic representation of experimental setup

30 40 50 60 70 80 90 100 110 120

-3.8

-3.6

-3.4

-3.2

Migration Time (sec)

PMT

Sign

al (A

.U.)

0.0008 0.0006 0.0004

Mobility (cm2 / V sec)

S G F

System peak

Sugar Separation in PDMS Device at pH = 12.3

System peak

30 40 50 60 70 80 90 100 110 120

pH = 12.6

pH = 12.3

pH = 12.0

pH = 11.5

PMT

Sign

al (A

.U.)

Migration Time (sec)

0.0008 0.0006 0.0004

Mobility (cm2 / V sec)

S G F

G

S/G/F

S/G/F

SPS F

Effect of pH on Carbohydrate Separations

SP

SP

SP

Self Referencing Chip Design-EOF Instability

• Capillary Electrophoresis Microchips– From J. Monahan thesis:

• High pH stability• Electroosmotic flow in native PDMS

channels• Retention times have poor

reproducibility• Dye/EOF marker partitioning

• Design chip geometry to account for drift due to changes in EOF, PDMS surface, pH, temp.

• Split analyte plug down two paths of differing lengths

• Recombine for detectionBuffer Waste

Analyte ReservoirAnalyte Waste

Buffer reservoir

Pat

h 1

Pat

h 2

Detection Area

100 150 200 250 300 350

1.0 V

Time /sec

PM

T S

igna

l /V

FITC1 FITC2

FL1 FL2

-50 0 50 100 150 200Adj. Time /sec

(a) (b)

Drifting Migration Times in Split Channel

Aligned to 1st peakFL-FITC separations

4 sequential runs

Split Channel for CE Standardization

• Split analyte plug down two paths of differing lengths

• Recombine for detection

Buffer Waste

Analyte ReservoirAnalyte Waste

Buffer reservoir

Path

1

Path

2

Detection Area

Standardizationj

obsy

obsystd

obsxj

obsx

obsxjx )()()()( 12112

"' µµµµµµ −−+−=FITC2

jobsx

obsxstd

obszj

obsz

obszjz )()()()( 12112

"' µµµµµµ −−+−=FA2

jobsx

obsxstd

obsyj

obsy

obsyjy )()()()( 12112

"' µµµµµµ −−+−=FL2

jobsy

obsystd

obsxj

obsx

obsxjx )()()()( 12112

"' µµµµµµ −−+−=FITC2 jobsy

obsystd

obsxj

obsx

obsxjx )()()()( 12112

"' µµµµµµ −−+−=FITC2

jobsx

obsxstd

obszj

obsz

obszjz )()()()( 12112

"' µµµµµµ −−+−=FA2 jobsx

obsxstd

obszj

obsz

obszjz )()()()( 12112

"' µµµµµµ −−+−=FA2

jobsx

obsxstd

obsyj

obsy

obsyjy )()()()( 12112

"' µµµµµµ −−+−=FL2 jobsx

obsxstd

obsyj

obsy

obsyjy )()()()( 12112

"' µµµµµµ −−+−=FL2

Adjusted µa

Observed µa2 Path 2

Set µa1 of Path 1 as reference

Standardize µa1of all devices

Compensate for EOF

within runs

FITC1 FL1 FA1 FITC2 FL2 FA2 FA2Average 96.2 105.7 135.4 179.7 197.4 254.2

Migration Time STD DEV 13.8 15.6 21.9 26.7 30.2 42.4%RSD 14.4 14.8 16.1 14.9 15.3 16.7Average 2.64E-04 2.41E-04 1.88E-04 2.05E-04 1.87E-04 1.46E-04

Mobility STD DEV 1.4E-05 1.4E-05 1.4E-05 1.1E-05 1.2E-05 1.1E-05%RSD 5.3 5.8 7.4 5.7 6.4 7.5Average 2.69E-04 2.56E-04 2.14E-04 2.09E-04

Adjusted Mobility STD DEV 9.8E-07 9.8E-07 2.4E-06 1.8E-06%RSD 0.4 0.5 1.1 0.9

( )j

eofy )12( −∆µ ( )

j

eofy )12( −∆µ( )

j

eofx )12( −∆µ ( )

j

eofx )12( −∆µ

50 100 150 200

Time /sec

PMT

Sign

al /a

.u.

0.4 V

FITC1

FITC2

FL2

FA2

FA1

FL1

Summary data for 15 separations

3 component separations

FL=fluoresceinFITC=fluorescein-isothiocyanateFA=fluorescein-amine

Monolithic Valves and Pumps

• Multilayer structures are constructed by binding layers of PDMS

• Useful for fluidic manipulation for lab-on-a-chip

Unger, M., et.al., Science 2000, 288, 113.

3D Microfluidics

Patterns of Cells and Proteins

Whitesides, G. M., et al., Proc. Nat. Acad. Sci. USA 2000, 97, 2409.

Laminar

Takayama, S., et al. Proc. Natl. Acad. Sci. U.S.A. 1999, 96, 5545.

Laminar Flow Patterning

Depletion Gradients

Fosser, K. A.; Nuzzo, R. G. Anal. Chem. 2003, 75, 5779.

Charge Patterning

Whitesides, G. M. MRS Bull. 2002, 27, 56-65.

Exposed Area

Exposed Area

Catalytic Patterning

Michel, B.; Bernard, A., et al. IBM J. Res. & Dev. 2001, 45, 697.

Catalytic Amplification

Harada, Y.; Girolami, G. S.; Nuzzo, R. G. Langmuir 2003, 19, 5114.

Phase-Shift Lithography

Schmid, H., et al. J. Vac. Sci. Technol. B. 1998, 16, 3422. Michel, B.; Bernard, A., et al. IBM J. Res. & Dev. 2001, 45, 697-717.

patterned gold lines

Microlens Patterning

Wu, M.; Whitesides, G. M.; J. Micromech. Microeng. 2002, 12, 747-758.

NanoTransfer Printing (nTP)

Zaumseil, J., et al. Nano Lett. 2003, 3, 1223.

Decal Transfer Lithography

Master and PDMS

UVO TreatmentOf PDMS

Heat or UV exposure

Adhesive PatternTransfer

10 µm

2 µm

Layer-By-Layer Printing (LBL)

Park, J.; Hammond, P. T. Adv. Mater. 2004, 16, 520.

Rogers et al., Proc. Nat. Acad. Sci. USA 2001, 98, 4837.

Flexible and Non-Planar Substrates

Whitesides, G. M., et al. Adv. Mater. 1999, 11, 7.

Problem and Solution?

d≥20h(h/l) range is 2.0-0.2

d (.2-20 µm); h (.5-200 µm); l (0.5-200 µm)

Sylgard 184

h-PDMSMichel, B.; Bernard, A., et al. IBM J. Res. & Dev. 2001, 45, 697. Xia, Y.; Whitesides, G. M. Ann. Rev. Mater. Sci 1998, 28, 153.

Improved Materials

Odom, T. W., et al. Langmuir 2002, 18, 5314.

Lat

eral

Hybrid Stamps

Michel, B.; Bernard, A., et al. IBM J. Res. & Dev. 2001, 45, 697.

2 layer stamp w/ glass backing

trilayer 2 layer w/ polymer backing

Fabrication of High Performance Ceramic Microgear

• Free-standing mm-sized gear of borosilicon carbonitride (SiBNC)

• Can withstand harsh thermal and oxidative environments

Yang, H., et.al., Adv. Mater. 2001, 13, 54.

Metal-oxide-semiconductor field effect transistor (MOSFET)

Jeon, H., et.al., Adv. Mater. 1998, 10, 1466.

Half-Wave Rectifier

Deng, T., et.al., Sens. and Act. 1999, 75, 60.

Magnetic Microfiltration

• Magnetic filtration allows for removal of paramagnetic and ferri(o)magneticparticles from diamagnetic fluids

• Arrays of micron-scale nickel posts were fabricated by soft lithography and electrodepostion

• Magnetic filters integrated into microfluidic systems reduces the size of the system

Deng, T., et.al., Appl. Phys. Lett., 2002,80, 461.

Light-emitting Diodes

• Soft contact lamination provides a means for establishing electrical contacts at room temperature in ambient conditions

• Applications: – Conformable light sources – Nanoscale optoelectronics

Lee, T., et.al.,PNAS 2004, 101, 429.

Patterning Spherical Surfaces

• Uses in optical and sensing devices with wide fields of view (>60º)

• Limits of lithography– Depth of focus limits

topography to ±λ/2– Planar mask only comes

into contact a single point – only a small area will be in

focus

Paul, K., et.al., Adv. Funct. Mater. 2003, 13(4), 259.

Thin-Film Transistors

• TFTs are used to address pixels in flat panel displays

• Eye focuses images on a spherically curved retina

Erhardt, M., et.al.,Chem. Mater. 2000, 12, 3306.

Microcontact Printing DNA

S.A. Lange, V. Benes, D.P. Kern, J.K.H. Horber, A. Bernard, Anal. Chem. 2004, 76, 1641.

Microcontact Printing Proteins

H. Wolf et al. IBM Journal of Research & Development. 2001, 45, 697.

Affinity Contact Printing of Proteins

J.P. Renault, A. Bernard, D. Juncker, B. Michel, H.R. Bosshard, E. Delamarche, Angew. Chem. Int.Ed. 2002, 41, 2320.

Separation of Biomolecules

Tryptic digest of FITC-BSA

S. Sia, G.M. Whitesides, Electrophoresis. 2003, 24, 3563.

Immunoassays

A. Bernard, B. Michel, E. Delamarche, Anal. Chem. 2001, 73, 8.