Transcript Slide 1
A Novice’s View of E-Beam Lithography Jan M. Yarrison-Rice Physics Dept. Miami University/University of Cincinnati w/ Sebastian Mackowski & Scott Masturzo -- UC Raith 150 User Meeting Stanford University September 29 & 30, 2003 Brief History of Raith 150 at University 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 Interests • Surface Enhanced Microscopies, e.g. SERS • Pickup Coils for Magnetic Field Sensing • Electrochemical Sensing Exposure Schedule for Dimers • Photonic Bandgap (PBG) Structures Lithographic 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 Processing a) Prepared Silicon Wafer b) Exposed Resist PMMA Silicon Dioxide Silicon c) Developed Resist e) Evaporated Metal d) f) Etched Silicon Dioxide Completed Co-planar Electrodes E-beam Source Source Properties source 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 ~108 20 nm 0.9 10-9 ~109 5 nm 0.22 10-10 thermal (Schottky) field emitter cold field emitter Block Diagram of E-beam E-Beam Column Charging on Sample Exposure Matrices Proximity Effect Evidence of Proximity Methods around Proximity Other Methods Surface Enhanced Spectroscopy Surface Enhanced Microscopies • Dimers – sharp edged doublets • Ag or Au - on glass for optical access • Size determined by plasmon frequency of nonlinear system Challenges.. – Sharp corners – Closely spaced nanoparticles 100 nm square dimers separated by 50 nm Pick-Up Coils • Contact Pads (~200 mm) • Coil lines (300 - 400 nm) • Challenges: Pick-up coil from a Distance – Sharp corners – Proximity effect of multiple lines – Overlap of write-fields Pick-Up Coil – Close Up Electro-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 #1 • 200 nm digits • Separation 200 nm • 495 PMMA A12 on Silicon ~100 nm thick Challenges – Strong proximity effect – Write field overlap – Very different sized structures combined Interdigitated Array #2 • 150 nm digits • Separated by 400 nm • ITO on Glass • 495 PMMA A12 to 100 nm thick PBG Structures Oxide cover layer (75nm) Nitride core (250 nm) • 2D arrays of etched pores Oxide buffer (1.8 mm ) • Particular Structures of Interest include: Substrate 260 nm 22 260 nm x nm y 5 450 nm – De-multiplexer – Polarization Switching – Microcavity for Sensing PBG Structure Requirements • • • 2D Triangular arrays of 150 nm etched holes Pitch ~ 250 nm Silicon nitride/silicon dioxide planar waveguide substrate Challenges – – Large field patterning – write field overlap & registration Two-step etching process Lithography 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.. EVERYTHING else!! - from making contacts, to metallic coatings, to liftoff All advice is welcome!