Jan M. Yarrison-RiceJan M. Yarrison-RicePhysics Dept.Physics Dept.

Miami University/University of Miami University/University of CincinnatiCincinnati

Raith 150 User MeetingStanford University

September 29 & 30, 2003

A Novice’s View of E-Beam A Novice’s View of E-Beam LithographyLithography

w/ Sebastian Mackowski & Scott Masturzo -- UC

Brief History of Raith 150 at Brief History of Raith 150 at University Of CincinnatiUniversity Of Cincinnati

• NSF MRI Grant funded August 2002

• Instrument installed July 2003

• Initial training sessions July 7-11

• Small groups (2-3) begin design & exposure July to present

2 micron squares exposed on silicon w/ 100 nm PMMA

Research InterestsResearch Interests• Surface Enhanced

Microscopies, e.g. SERS

• Pickup Coils for Magnetic Field Sensing

• Electrochemical Sensing

• Photonic Bandgap (PBG) Structures Exposure Schedule for Dimers

Lithographic RequirementsLithographic Requirements

• 50 to 200 nm feature sizes

• Inter-feature spacing as small as

50 nm

• Pattern on ITO glass, silicon, or silicon nitride/dioxide

Exposure and ProcessingExposure and Processing

Silicon Dioxide

PMMA

Silicon

a) b)Exposed Resist

c)d)

Developed Resist Etched Silicon Dioxide

Evaporated Metal Completed Co-planar Electrodes

e)f)

Prepared Silicon Wafer

E-beam SourceE-beam Source

Source PropertiesSource Propertiessource type brightness

(A/cm2/sr)source size energy spread

(eV)vacuum

requirement(Torr)

tungsten thermionic

~105 25 um 2-3 10-6

LaB6 ~106 10 um 2-3 10-8

thermal (Schottky) field emitter ~108 20 nm 0.9 10-9

cold field emitter ~109 5 nm 0.22 10-10

Block Diagram of E-beamBlock Diagram of E-beam

E-Beam ColumnE-Beam Column

Charging on SampleCharging on Sample

Exposure MatricesExposure Matrices

Proximity EffectProximity Effect

Evidence of ProximityEvidence of Proximity

Methods around Methods around ProximityProximity

Other MethodsOther Methods

Surface Enhanced Surface Enhanced SpectroscopySpectroscopy

Nanoscale sample

SIL lens

Microscopeobjective

Spectrometer

Ag nanoparticlearray

Bottom view of SILlens with nanoparticle array3 axis

Stage

Laser

CCD

View of Entrance Slit(rotation of etalon shiftsrows of spectra into slit)

800 pixels

2000 pixels

View of CCD camera

Surface Enhanced MicroscopiesSurface Enhanced Microscopies• Dimers – sharp edged

doublets

• Ag or Au - on glass for optical access

• Size determined by plasmon frequency of nonlinear system

Challenges..Challenges..– Sharp corners– Closely spaced

nanoparticles 100 nm square dimers separated by 50 nm

Pick-Up CoilsPick-Up Coils• Contact Pads (~200 m)

• Coil lines (300 - 400 nm)

• Challenges:– Sharp corners– Proximity effect of multiple

lines– Overlap of write-fields

Pick-up coil from a Distance

Pick-Up Coil – Close UpPick-Up Coil – Close Up

Electro-Chemical SensorsElectro-Chemical Sensors• Interdigitated Arrays

– Long 100 to 500 nm thick fingers w/ ~50 nm separation

– Large contact Pads separated by mm

– Au or Ag on glass

Top: 500 nm digits, Bottom: 200 nm digits

Interdigitated Array #1Interdigitated Array #1• 200 nm digits

• Separation 200 nm

• 495 PMMA A12 on Silicon ~100 nm thick

Challenges -Challenges - – Strong proximity effect– Write field overlap– Very different sized

structures combined

Interdigitated Array #2Interdigitated Array #2• 150 nm digits

• Separated by 400 nm

• ITO on Glass

• 495 PMMA A12 to 100 nm thick

PBG StructuresPBG Structures• 2D arrays of etched

pores

• Particular Structures of Interest include:– De-multiplexer– Polarization Switching– Microcavity for

Sensing

Oxide cover layer (75nm)

Nitride core (250 nm)

Oxide buffer (1.8m)

Substrate

nm

nm

nm

nm

y

x

PBG Structure PBG Structure RequirementsRequirements

• 2D Triangular arrays of 150 nm etched holes• Pitch ~ 250 nm• Silicon nitride/silicon dioxide planar waveguide

substrate

Challenges -Challenges - – Large field patterning – write field overlap &

registration– Two-step etching process

Lithography ChallengeLithography Challenge• Best practices to make small,

closely spaced features – Design of structure– Dosage choices– Aperture choice– Resist

• What we have tried to date– Dosage schedules within feature for proximity– Lines around area features to sharpen edges– Dots and their use to sharpen corners

Other Challenges..Other Challenges..

EVERYTHING else!!

- from making contacts, to metallic coatings, to liftoff

All advice is welcome!All advice is welcome!