MEMS Fabrication By Thomas Szychowski

MEMS overview Micron level mechanical parts Made from transistor materials and metals Van Der Waals forces Intermolecular bonding Plays an important part in design

Fabrication Techniques Mask Lithography Injection molding Microstereolithography Silicon Surface Micromachining Silicon Bulk Micromachining

Mask Lithography Use of photo resist Multiple layers – Multiple steps 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 lithography Metal poured over resist Resist gets dissolved Metal 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 capabilities Lateral 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 ?

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