1. Etching Processes for Microsystems Fabrication

2. Overview Micro Systems Micro Devices Etching Process
Etching Parameters
Qualitative Reasoning

3. Presented by:
Arman Ur Rashid

4. Microsystems

5. Micro devices: Neural Probes
100um
10nm

6. Micro Devices: Microgear and Alignment Pin
Substrate
Gear
[Courtesy of Sandia National Laboratories]

7. Microsystems Etch Processes
Wafer Surface
Below the Surface
Within the substrate

8. Etching Process
Deposition
Photolithography
Etch
Pattern Transfer

9. Etch Parameters

10. Etch Rate=
ETCH RATE

11. Etch Profile Isotropic Etching Anisotropic Etching
Isotropic Etch Profile
Anisotropic Etch Profile

12. Poor selectivity -> 1:1 Good selectivity -> 100:1
Ef = etch rate of the film undergoing etch
Er = etch rate of the photoresist
Poor selectivity -> 1:1
Good selectivity -> 100:1

13. Etch Process: Wet Etching Dry Etching Chemical Process
Chemical or Physical Process

15. Overview of Dry Plasma Etch
Substrate
Etch process chamber
Exhaust
Gas delivery
RF generator
Cathode
Anode
1) Etchant gases enter chamber
Electric field l l
Anisotropic etch
Isotropic etch

16. Chemical Versus Physical Dry Plasma Etching

17. Down Stream Reactor

18. Ion Beam Etcher _ + + Screen grid Accelerating grid
Hot filament emits electrons
Gas inlet
(Argon)
To vacuum system
Neutralizing filament
Accelerating grid
Screen grid
Electromagnet 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
Figure 16.18

19. Deep Reactive-Ion Etching (DRIE):
The Bosch Process
The Cryogenic Process

20. Illustration of The Bosch Process:
SF6 plasma
F+ions
Mask
SF6 plasma
SiF4
C4F8 plasma
Si Substrate

21. Illustration of The Bosch Process(Cont):
Oxide Hard mask
SF6 plasma
C4F8 plasma
C4F8 plasma
SF6 plasma
Passivation in First Cycle
Etch Stage in First Cycle Etch
C4F8 plasma
C4F8 plasma
C4F8 plasma
SF6 plasma
SF6 plasma
Second Etch
Passivation Removal
After 4th Cycle Etch

22. SEM Graph:

23. Characteristics of The Bosch Process:
Roughness of Sidewall
Aspect Ratio
90 Degree Edge

24. Challenge of The Bosch Process:
Multiple Deposition Parameters
Multiple Etching Parameters
Variation of Etch Rate depth
Notching Effect Si
SiO2
x min Etching
Notching Si
SiO2
x min + overetch time

25. Notching in SEM Graph:
Notching

26. Illustration of The Cryogenic process:
SiF4
F+ions
SF6 plasma
Mask
Ultra thin layer of SiO2 Si

27. SEM Graph:

28. Characteristics of The Cryogenic Process:
Low Ion Energies
Little Physical Etching on The Mask Surface
High Selectivity.
Low Sidewall Roughness
High Etch Rate

29. Why Cryogenic Temperature:
Condensation on Surfaces
Spontaneous Chemical Reaction
Etch Rate of the Mask Material

30. 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
Low Etch Rate
High Etch Rate

31. Comparison of The Bosch and Cryogenic Process:
Sidewall
Etch Rate
Selectivity
Cracking of Mask

32. Summary Etching Process Parameters Dry Plasma Etching Techniques
Deep Reactive Ion Etching
DRIE Procedures and Challenges