1. MEMS, Fabrication
Cody Laudenbach

2. Overview MEMS overview Electronics Fabrication Bulk Micromachining
Chemical Wet Etching
Isotropic vs anisotropic
Deep Reactive Ion Etching
Surface Micromachining
Molding
LIGA

3. MEMS Overview Microelectromechanical Systems Micrometer scale devices
Can range from microns to
millimeters
Integrates electrical and
mechanical parts
Can be merged onto SI
substrate with IC’s
Pressure sensors and
gyroscopes
Must have some mechanical functionality, whether the parts move or not

4. Electronics Fabrication
Fabricated using IC processes
Etching
Wet
Dry
Lithography
Photoresist Coating
Masking
Light exposure

5. Bulk vs Surface micromachining
Bulk Micromachining
Bulk micromachining is the selective removal of substrate material
Surface Micromachining
Surface micromachining is the deposition of thin film in alternating layers, with the sacrificial layer being removed altogether at the end of the process

6. Bulk Micromachining Chemical wet etching Isotropic Anisotropic
Not dependent on crystallographic orientation
Theoretically would etch in all directions at equal rates
Silicon dioxide or silicon nitride typically used as masking
Anisotropic
Dependent on crystallographic orientation
Etches much faster along <100> crystalline plane than that of the <111> plane
Etch rates dependent on chemicals used such as KOH (Potassium Hydroxide)

7. Bulk Micromachining (Cont.)

8. Bulk Micromachining (Cont.)
Deep Reactive Ion Etching
Bosch process
Process
Dry plasma etch
Alternates between etching and coating an etch resistant polymer layer on the side walls
The layer at the bottom of pit is etched faster than that of the side walls

9. Deep Reactive Ion Etching

10. Surface Micromachining
One of the most common methods of manufacturing MEMS devices
Process
Films are deposited on substrate, typically alternating between sacrificial and structural layers
Patterned through photolithography
Sacrificial parts removed, typically through wet chemical etching
Results in parts that are able to move relative to the substrate
Early processes used Polysilicon as structural layers and some form of silicon oxide for the sacrificial layer.
metals, oxides and nitrides of silicon, and polymers have been used for both structural and sacrificial films.

11. Surface Micromachining (Cont.)

12. Molding
LIGA
German acronym for Lithography, Electroplating, and Molding
Originally used x-ray source to expose layers out of photosensitive material
Current processes use visible light or UV light sources for creating molds

13. Summary
Microelectromechanical systems are a combination of electrical and mechanical components on the micrometer scale
Electronic components created using IC fabrication processes, such as etching and lithography
Mechanical components created through bulk micromachining, surface micromachining and molding
Bulk micromachining is done through wet chemical etching or Deep Reactive Ion Etching
Surface micromachining done through alternating structural and sacrificial film layers, then removing sacrificial layers
Molding uses photolithography to etch out molds that are then used to create micromechanical parts

14. References
"7.2.1 Important MEMS Processes." Important MEMS Processes. N.p., n.d. Web. 07 Apr < r7_2_2.html>. "Deep Reactive-ion Etching." Wikipedia. Wikimedia Foundation, 26 Feb Web. 07 Apr < "Fabricating MEMS and Nanotechnology." MNX. N.p., n.d. Web. 07 Apr.2017.< "Introduction to Microelectromechanical Systems (MEMS)." Introduction to Microelectromechanical Systems (MEMS) | Compliant Mechanisms. BYU, n.d. Web. 07 Apr < content/introduction- microelectromechanical-systems-mems>. "Semiconductor Device Fabrication." Wikipedia. Wikimedia Foundation, 30 Mar Web. 07 Apr < "What Is MEMS Technology?" What Is MEMS Technology? N.p., n.d. Web. 07 Apr <

15. Five takeaways
MEMS are a combination of electronic and mechanical components on the scale of micrometers
Differences: bulk micromachining is the selective removal of substrate material, while surface micromachining is deposition of thin film in alternating layers, with the sacrificial layer being removed altogether at the end of the process
DRIE is the process of a dry plasma etching alternating with an etch resistant polymer which allows for a high aspect ratio
Anisotropic wet chemical etching is more widely used as it has a higher resolution etching capability
Molding is another process of which photolithography is used to create a mold for micromechanical components to then be formed with