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Process technology

Process technology. 70 nm. Luft. InP. Applications: Nano Devices. Nanoelectronics. Basic Research. Magnetoelectronics. MMIC-HEMT, ETH Zürich. Electrical nm contacts, Uni Basel. TH Aachen. Nano-“mechanics“. Optics. EBL. L =230 nm. DFB Laser, WSI München. „Nanopendulum“, LMU.

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Process technology

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  1. Process technology

  2. 70 nm Luft InP Applications: Nano Devices Nanoelectronics Basic Research Magnetoelectronics MMIC-HEMT, ETH Zürich Electrical nm contacts, Uni Basel TH Aachen Nano-“mechanics“ Optics EBL L=230 nm DFB Laser, WSI München „Nanopendulum“, LMU

  3. substrate Spin coating Wafer resist substrate Exposure After x process steps Coating or stripping step substrate Developing substrate Lift-Off Etching Pattern Transfer metal Remover Remover Process Technology

  4. substrate substrate Spin coating resist substrate Exposure gas injection EBID substrate Developing substrate Lift-Off Etching metal Pattern Transfer substrate metal Etching Remover Remover Process Technology

  5. substrate Spin coating resist Raith support substrate Exposure Special Knowledge, e.g. EBL resist database substrate Developing substrate Lift-Off Etching Pattern Transfer metal Remover Remover General Knowledge Process Technology

  6. Instrumentation • wet bench • (eye-) shower for • accidents with acids • storage for chemicals • stove / hotplate • refrigerator • spin coater • stove / hotplate • Film Thickness Probe • Raith 150 / R50 FE • wet bench • storage for chemicals • optical microscope • sputtering machine • Raith 150/ R50 FE Cleaning Cleaning substrate Spin coating Spin coating Spin coating substrate Film thickness measurement Film thickness measurement Exposure Exposure Exposure substrate Developing Developing Developing substrate Inspection Inspection Raith Application Lab: Typical Instrumentation Process step

  7. Lift Off • Tips & Tricks • obtain an undercut resist profile by • using a double layer resist • using low beam energy • overexposure or • overdeveloping • use an aspect ratio of resist: • metal as large as possible • if possible use evaporation, • not sputtering

  8. Wafer Wafer Etching • Tips & Tricks • obtain cross-sections without • undercut or overcut by • using high beam energy • avoiding overexposure and overdeveloping Resist • apply postbake to improve resist stability during etching • for organic resists avoid etching processes with oxygen

  9. Process Steps substrate Spin coating Wafer resist substrate Exposure • inspection • e.g. resist thickness • measurement e.g. electron beam lithography substrate Developing substrate • inspection • optical microscope • SEM • metrology

  10. How to Avoid Charging Effects • On isolating samples an additional metal layer between resist an substrate or on top of the resist is required, e.g. • use additional Al layer on top of the resist. • thickness should be 10 nm to 20 nm • remove with KOH • With an additional isolating interlayer, e.g. SiO layer • use a higher acceleration voltage, e.g. 25 kV for 1 µm SiO.

  11. Resist Characterization I: Dependence of thickness on spin speed open cover closed cover

  12. Resist Characterization II: Contrast curves

  13. Positive EBL Resists • application dose resolution comments • µC/cm2 @30keVnm • High resolution: • PMMA ~200 <10 dry etch (--), low sensitivity or low contrast • ZEP xx ~ 50 <20 dry etch(3x better than PMMA), adhesion (-) • Mask making: • EBR-9 ~20 >200long shelf life, large process latitude • PBS ~2 >250 low contrast, difficult process (--) • AZ5206 ~20 ~250 high contrast, good etch resistance • Double layer with PMMA (e.g. lift-off): • P(MMA-MAA) ~ 70 <200 • PMGI ~ 40 <100 more info at: http://cnf.cornell.edu/ebeam/resist.html www.microresist.de http://snf.stanford.edu/process/lithography/ebeamres.html www.allresist.de www.microchem.com

  14. Negative EBL Resists • Application dose resolution comments • µC/cm2 @30keVnm • High resolution • Calixarene ~4000 <10 very low sensitivity, high resolution (+) • HSQ ~300 <20 dry etch(+) • ma-N2400 ~100 <70DUV & E-beam sensitive • NEB xx ~ 20 <40 dry etch(+), adhesion (-) • SAL ~10 <100high contrast, dry etch (+) • SU8 ~2 <100 3D EBL applications • COP ~1 >1000 difficult process (--) • Mask making more info at: http://cnf.cornell.edu/ebeam/resist.html www.microresist.de http://snf.stanford.edu/process/lithography/ebeamres.html www.allresist.de www.microchem.com

  15. Which Resist for Which Task? • decide about positive or negative resist with respect • to the minimum area that will be exposed • check literature and resist suppliers for resist • performance with respect to e.g. • resolution • sensitivity • etching stability • check suitability for your lab, e.g. required baking • steps and chemicals

  16. Getting Started • As an EBL beginner, use resists that are easy to handle: • avoid chemically amplified resist because they need a carefully controlled post exposure bake • avoid very sensitive resists • make first tests with positive resist, because several tests can be made on one sample • use for example PMMA 950K from Raith’s EBL starter kit

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