MEMS Fabrication

By

Thomas Szychowski

MEMS overviewMicron level mechanical parts

Made from transistor materials and metals

Van Der Waals forces Intermolecular bonding Plays an important part in design

Fabrication TechniquesMask Lithography Injection moldingMicrostereolithographySilicon Surface MicromachiningSilicon Bulk Micromachining

Mask LithographyUse of photo resist

Positive Dissolves under light

Negative Hardens under light

Both get covered with desired material, then photo resist is dissolved by a solvent

Multiple layers – Multiple steps

Mask Lithography

Injection Molding

Starts with mask lithographyMetal poured over resistResist gets dissolvedMetal form is left for plastic injection

molding

Injection Molding

Microstereolithography

Similar principal to mask lithography, but for 3D pieces Uses an “active mask”

Not a physical mask Utilizes a photo-reactive acrylic resin Each layer image projected through a DMD(digital mirror

device) Projected into the resin

Uses lenses Resin that is illuminated, Cross-links and hardens Piece is then covered in a hardened layer

Microstereolithography

Dimensional capabilitiesLateral and Vertical resolution: 10μm Maximum field size: 10.24mm x

7.68mm Structural height: up to 5mm

Microstereolithography

Microstereolithography

Silicon Surface Micromachining Uses the same process as IC fabrication Needs multiple layers to create structures Cheapest form of Micromachining Similar to lithography

Sacrificial material Structural material

When sacrificial material is removed, only whole structures are left

Silicon Surface Micromachining

Silicon Surface Micromachining

Silicon Surface Micromachining

Silicon Bulk Micromachining

Done with Crystalline silicon Constructed using etch stop planes Chemical process Anisotropic Etching

Speed dependent – Directional etch in different crystallographic directions at

different rates Slower directions create and etch stop plane

Deep Reactive Ion Etching (DRIE)

Uses photo resist and a mask to create structures

Sapphire Etching

Metal Mask 100µm etch depth .28µm/min etch rate Chlorine etching

Pressure Sensor Etching

Used on silicon Metal mask .81µm etch depth Utilizes Fluorine

High-Speed Etching

Silicon material 1µm/min etch rate W-Si Mask

Whacky Neato Pictures

Questions

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References http://home.earthlink.net/~trimmerw/mems/tour.html http://home.earthlink.net/~trimmerw/mems/BM_bulk.h

tml http://www.samcointl.com/apps/mems.html http://www.cmf.rl.ac.uk/latest/msl.html http://www.chemguide.co.uk/atoms/bonding/vdw.html “Micromachining for Optical and Optoelectronic

Systems”. MING C. WU