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ME 381R Fall 2003 Micro-Nano Scale Thermal-Fluid Science and Technology Lecture 18: Introduction to MEMS

ME 381R Fall 2003 Micro-Nano Scale Thermal-Fluid Science and Technology Lecture 18: Introduction to MEMS. Dr. Li Shi Department of Mechanical Engineering The University of Texas at Austin Austin, TX 78712 www.me.utexas.edu/~lishi lishi@mail.utexas.edu. Outline. MEMS: Applications

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ME 381R Fall 2003 Micro-Nano Scale Thermal-Fluid Science and Technology Lecture 18: Introduction to MEMS

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  1. ME 381R Fall 2003 Micro-Nano Scale Thermal-Fluid Science and Technology Lecture 18: Introduction to MEMS Dr. Li Shi Department of Mechanical Engineering The University of Texas at Austin Austin, TX 78712 www.me.utexas.edu/~lishi lishi@mail.utexas.edu

  2. Outline • MEMS: Applications • Pattern transfer Method • - Lithography • Subtractive Method • - Wet and Dry Etching • Additive Method • - Thin Film Deposition • Example (Cantilever Beam) } Basic Fabrication Techniques

  3. MEMS Applications http://mems.colorado.edu/c1.res.ppt/ppt/g.tutorial/ppt.htm

  4. MEMS Applications http://mems.colorado.edu/c1.res.ppt/ppt/g.tutorial/ppt.htm

  5. MEMS Applications http://evlweb.eecs.uic.edu/scharver/asci/mems.html This image depicts a mirror system moved by a small rotating gear

  6. MEMS Fabrication Techniques • Pattern Transfer Method : • Photo Lithography • E-beam Lithography • Nano-imprinting Lithography • Subtractive Method : • Wet Etching • Dry Etching • Additive Method : • Thin Film Deposition

  7. Photolithography • Energy • Change cross linking of polymer chains of a photo-sensitive polymer called photoresist, and modify its dissociation rate in a developer similar to that for developing photos • Mask • Absorber (Dark Area) & window (Open area) • Resist • Transfer image from mask to wafer

  8. Photolithography • Positive Photoresist • - the polymer is weakened • and more soluble in • the developer • Negative Photoresist • - the polymer is hardened • and less soluble http://www.ece.gatech.edu/research/labs/vc/theory/photolith.html

  9. Photolithography Exposure Systems • Contact – not limited by diffraction • Proximity – 2 ~ 20 m gap, limited by diffraction • Projection – limited by diffraction

  10. Electron Beam Lithography • Minimum beam size (5nm) • for optical & X-ray masks, and nano-devices • Direct writing on resist-coated substrate • No Mask

  11. Energy Sources Energy Sources • Energy • Minimum Line Width

  12. Comparison Comparison

  13. Nano-imprinting Lithography: Step and Flash Imprinting Lithography (S-FILTM) Courtesy: Profs. C. G. Willson & S.V. Sreenivasan, UT Austin

  14. S-FIL Patterned Nanowires Sub-40 nm contacts 30 nm dense lines 20 nm isolated lines Courtesy: Profs. C. G. Willson and S.V. Sreenivasan

  15. Subtractive MethodWet and Dry Etching • Wet Etching • Chemical Reaction • Liquid source • Dry Etching • Chemical + Physical Reaction • Gas or Vapor phase source http://www.ee.ucla.edu/~jjudy/classes/ee150L/lectures/EE150L_Lecture_Dry_Etching_files/frame.htm

  16. Etching Mechanism http://www.ee.ucla.edu/~jjudy/classes/ee150L/lectures/EE150L_Lecture_Dry_Etching_files/frame.htm

  17. Dry Etching Ion Energy • Physical Etching (Sputtering) • Momentum transfer •  bond breakage • Particle Collisions • Aniosotropic • Physical- chemical Etching • Ion bombardment to make • the surface more reactive • Anisotropic • Chemical Etching • Reactive etchant species • Isotropic Pressure

  18. Silicon Crystal Structure

  19. Isotropic and Anisotropic in Wet and Dry Etching For Silicon - HNA (HF, HNO3, CH3COOH)

  20. Comparison

  21. Etching Process http://www.saabmicrotech.se/node4084.asp

  22. Additive Method Thin Film Deposition • Physical Vapor Deposition (PVD) • Thermal Evaporation • Sputtering • Chemical Vapor Deposition (CVD) • PECVD (Plasma Enhanced) • LPCVD (Low Pressure) • Electroplating

  23. PVD: Thermal Evaporation • Thermal Evaporation • Low working pressure • to increase mean free path • Low surface damage • Faster than sputtering • Limited material • Based on the sublimation • Fast • Low surface damage • Difficult to control • Limited materials (metal) http://www.icmm.csic.es/fis/english/ evaporacion_resistencia.html

  24. PVD: Sputtering • Sputtering • Based on Ion bombardment • Unlimited material • Possible surface damage • Excellent adhesion • Expensive http://web.kth.se/fakulteter/TFY/cmp/research/sputtering/images/sputtering_anim.gif http://www.ee.ucla.edu/~jjudy/classes/ee150L/lectures/EE150L_Lecture_Dry_Etching_files/frame.htm

  25. CVD: Plasma Enhanced • PECVD • Plasma helps reaction • Low substrate temperature • Good step coverage • Chemical contamination http://www.seas.ucla.edu/Chang/pictures/ research-pecvd.jpg

  26. CVD: Low Pressure • LPCVD • < 10 Pa • Excellent purity • Low stress • High temperature • Low deposition rate http://www.memsnet.org/mems/beginner/ images/cvd_reactor.jpg

  27. Electroplating • Various metal (Au, Ni, etc) • Fast • > 10 m • Hydrogen bubble generation • Difficult for sub-m features • Needs seed layer J.W. Judy, "Magnetic microactuators with polysilicon flexures," Masters Report, Department of EECS, University of California, Berkeley, August 29, 1994

  28. Making a Cantilever Beam(Surface Micromachining)

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