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3 MEMS FABRICATION

MEMS MOEMS Nano. Workshop. 3 MEMS FABRICATION. Ken Gilleo PhD ET-Trends LLC. 24%. Silicon Aluminum Si 3 N 4 (Nitride) GaAs SiC Polymers. SiO 2 Copper Aluminum Polymers SiGe Silicon. MEMS Material Classes. Structures. Sacrificial.

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3 MEMS FABRICATION

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  1. MEMS MOEMS Nano Workshop 3 MEMS FABRICATION • Ken Gilleo PhD • ET-Trends LLC 24%

  2. Silicon Aluminum Si3N4 (Nitride) GaAs SiC Polymers SiO2 Copper Aluminum Polymers SiGe Silicon MEMS Material Classes Structures Sacrificial • Etchant or process will determine if material is structural or sacrificial

  3. Movable Structures • Pivots • Bearings • Hinges • Beams (bend/twist) • Gears • Rack • Wheels • Latch • Switches • Valves • Diaphragms • Turbines • Springs

  4. Stationary Structures • Base/platform • Reference mass • Chambers • Channels • Back plate (microphone) • Fittings/ports • Needles/blades

  5. MEMS Manufacturing • Use SEMICONDUCTOR processes • Silicon Machining; (1) surface, and (2) bulk: • Define mechanical parts by lithography • Form sacrificial SiO2 (or other) in “removal” areas • Etch away SiO2 to free mechanical parts • Many other micro-machining processes and variations are available

  6. Poly 4 sacrificial oxide 4 Poly 3 sacrificial oxide 3 Sandia Poly 2 Poly 1 sacrificial oxide 1 nitride oxide Substrate Sandia Sandia SUMMiT Process (Surface Machining Process) Sacrificial oxide 2 Poly 0

  7. MEMS Bulk Fabrication • Start with single crystal silicon • Apply etch resist (mask) • Can selectively implant stop etch into Si • Etch unwanted silicon • Wet/chemical (anisotropic; etches alone planes) • Dry plasma (high resolution) • Simpler shapes, lowest cost (?)

  8. Wet Etch Mask: SiO2, Si3N4 Etchant: KOH, org. base Etch Retarder: Boron (B) Dry Etch Deep Reactive Ion Etching (DRIE) SF6/O2 Gas 30:1 Aspect Ratio Si Wet or Dry Bulk Process membrane Si

  9. Bosch Processbest dry etch method Also being adopted for TSV (vias) • Plasma etch • Deposit resist • Plasma etch • Repeat 2, 3. Very high aspect ratios

  10. LIGA Process Lithographie Galvanoformung Abformung • LIGA mask design • Mask fabrication • Substrate preparation • X-ray exposure • X-ray resist development • Electroplate • Panelization • Replication

  11. Final step before packaging Oxide 2 Si MEMS Release • A critical very step • Remove holding structure • Wet Chem Etch; dissolve silica ; SiO2 • Dry Plasma Etch • Packaging foundry may run this process Remove sacrificial layer More fragile Etch & Release

  12. Wafer Bonding • Fabricate MEMS devices • Pumps, pressure sensors • Values, controllers • Chambers; analyzers, reactors • Integrated MEMS • Electronics; logic, memory, sensors • Optics, photonics • Pre-packaging; capping wafers • Complete Wafer-Level Package (WLP)

  13. Wafer Bonding Methods

  14. Summary of Fabrication • MEMS can use existing semiconductor mfg • Major boost with existing infrastructure • Parallel process; productivity • Older foundries 6” moving to 8” (don’t need 12”) • Combine CMOS logic & MEMS • MEMS can build almost any macrostructure • Cavities, electronics may require wafer bonding

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