Download - Surface MEMS 2014 Part 1 [email protected]
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Applications
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Generic structure
Sacrificial material
Structural material
Substrate material
Structural material
Substrate material
anchor
anchor
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Single mask vs. two mask cantileverSingle mask process Two mask process
mask #2
mask #1
mask
Etch structural layer with resist mask
Etch sacrificial layer without resist
Etch structural layer with resist mask
Etch sacrificial layer without resist
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Material pairs & etchants Structural film Sacrificial film Sacrificial etch(es)
polysilicon oxide HF, HF vaporsilicon nitride oxide HFsilicon nitride Al NaOH, H3PO4
nickel Cu HCl nickel resist oxygen plasma aluminum resist oxygen plasmagold Cu HClgold resist oxygen plasmacopper resist oxygen plasmaParylene resist acetone, other
solventsSU-8 Cu HCl
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HF etching of SiO2 and other materials
Etchant MaterialSiO2 TEOSPSG Si3N4 Al Mo
HF (49%) 176339694778 15 38 0.15BHF 133 107 1024 1 3 0.51:10 HF 48 157 922 1.5 320 0.15
Etch rates in nm/min
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Different silicon dioxide films
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AFM tips: surface release
Condition: Cr release etching must not attack Au or SU-8
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AlN unimorph suspensions
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Thermally excited resonator
1.Oxide deposition2.Poly deposition3.Lithography piezores4. I/I piezo doping & strip5.Anneal I/I6.Au depo7.Litho for heater8.Au heater etch & strip9.Poly etch & strip10.Oxide etch11.Rinse & dryoxide
poly
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Single mask SOI accelerometer
1. Device silicon DRIE
2. Buried oxide HF wet etch
3. Rinse & dry
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Optical spectrometer in SOI
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Compressive stresses in film
buckling
Depends on span on the structure: short beams do not buckle; and hard materials less prone than soft.
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Tensile stress in film
Desired stress state in most cases; too much tensile stress leads to cracking.
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Released structural layers
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Polysilicon
• Deposited by CVD at 625oC true poly• Can be deposited at 575oC amorphous• Anneal after deposition: a-Si poly !• Typical thickness 1-2 µm
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Polysilicon doping
• Usually deposited undoped (practically insulator)• Doping after deposition
– diffusion– implantation
• Annealing ~950oC, 1 h to activate dopants• Annealing changes film stress (and grain size)• Heavy doping ca. 500 µΩ-cm (cf. Al 3 µ Ω-cm )• Grain size ca. 200-300 nm after anneal
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Polysilicon stress anneal
580oC deposited film (a-Si)
annealed differently,
leading to different final stress
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Marc Madou
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Optical modulator/
interference filter/
display
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Metal micromechanics (1)
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Metal micromechanics (2)
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RF switch
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Electroplated gold switch
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Perforation to release large area structures
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End of surface MEMS 1