Post on 15-Jul-2015
Etching Processes for Microsystems
Fabrication
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Micro Systems
Micro Devices
Etching Process
Etching Parameters
Qualitative Reasoning
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Arman Ur Rashid
Microsystems
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Micro devices: Neural Probes
10nm
100um
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Micro Devices: Microgear and Alignment Pin
[Courtesy of Sandia National Laboratories]
Alignment Pin
Gear
Substrate
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Microsystems Etch Processes
Within the substrate
Wafer SurfaceBelow the Surface
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Etching Process
Deposition
Photolithography
EtchPattern Transfer
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Etch Parameters
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ETCH RATEEtch Rate=
T
t
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Etch Profile
Isotropic Etch Profile Anisotropic Etch Profile
Isotropic EtchingAnisotropic Etching
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SELECTIVITY
Ef = etch rate of the film undergoing etchEr = etch rate of the photoresist
Poor selectivity -> 1:1Good selectivity -> 100:1
f
r
ES
E
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Etch Process:
Wet EtchingChemical Process
Dry EtchingChemical or Physical Process
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Overview of Dry Plasma Etch
Substrate
Etch process chamber
Exhaust
Gas delivery
RF generator
Cathode
Anode
l
l
Anisotropic etch Isotropic etch
1) Etchant gases enter chamber
Electric field
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Chemical Versus Physical Dry Plasma Etching
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Down Stream Reactor
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Ion Beam Etcher
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Hot filament emits
electrons
Gas inlet
(Argon)
To vacuum system
Neutralizing filament
Accelerating gridScreen gridElectromagnet
improves ionization
Plasma chamber(+anode repels +ions)
Wafer can be tilted to control etch profile
Redrawn from Advanced Semiconductor Fabrication Handbook, Integrated Circuit Engineering Corp., p. 8-12.
Figure 16.18
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Deep Reactive-Ion Etching (DRIE):1. The Bosch Process
2. The Cryogenic Process
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Illustration of The Bosch Process:
SF6
plasmaSiF4
F+ions
Si Substrate
Mask
C4F8
plasma
SF6 plasma
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SF6
plasmaC4F8 plasma
SF6
plasma
Oxide Hard mask
Etch Stage in First Cycle EtchPassivation in First Cycle
C4F8 plasmaSF6
plasma
SF6
plasma
Passivation Removal
C4F8 plasma C4F8 plasma
Second Etch
After 4th Cycle Etch
C4F8 plasma
Illustration of The Bosch Process(Cont):
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SEM Graph:
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Characteristics of The Bosch Process:
Roughness of Sidewall
Aspect Ratio
90
Deg
ree
Ed
ge
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Challenge of The Bosch Process: Multiple Deposition Parameters
Multiple Etching Parameters
Variation of Etch Rate depth
Notching Effect
Si
Si
SiO2
x min Etching
Si
Si
SiO2
x min + overetch time
Notching
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Notching in SEM Graph:
Notching
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Illustration of The Cryogenic process:
SF6
plasma
SiF4F+ions Mask
Si
Ultra thinlayer of
SiO2
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SEM Graph:
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Characteristics of The Cryogenic Process:
Low Ion Energies
Little Physical Etching on The Mask Surface
High Selectivity.
Low Sidewall Roughness
High Etch Rate
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Why Cryogenic Temperature: Condensation on Surfaces
Spontaneous Chemical Reaction
Etch Rate of the Mask Material
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Challenges of The Cryogenic Process: Cracking of Masks
Sensitive to Heat Path Variations
Etch Rate Varies with Depth
Shape and Depth Depends on Multiple Parameter
Notching effect
Reduction in Etch Rate Due to Aspect Ratio
High Etch Rate
Low Etch Rate
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Comparison of The Bosch and Cryogenic Process: Sidewall
Etch Rate
Selectivity
Cracking of Mask
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Summary
Etching Process
Parameters
Dry Plasma Etching Techniques
Deep Reactive Ion Etching
DRIE Procedures and Challenges
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