HIGH ASPECT RATIO DEEP SILICON ETCHING

Table 3: Optimized etch characteristics including depth, aspect ratio, sidewall slope, and undercut vs. trench
width. The etch time is 150 min.
Mask
opening
Actual trench width (µm)
Top Middle Bottom
Trench
depth (µm)
Aspect
ratio
Sidewall
slope (⁰)
Undercut
(µm)
2.5 6.3 3 1.7 292 97.3 89.55 1.9
3.5 7.4 3.9 2.5 339 86.9 89.59 1.95
4.4 8.8 4.7 3.4 370 78.7 89.58 2.2
5.3 10 5.7 4.2 398 69.8 89.58 2.35
Aspect ratio
150
100
50
this work
[3]
[6]
[4]
0
0 2 4 6 8 10 12
Trench width (μm)
Figure 6: Aspect ratio of adjusted recipe compared to
state-of-the art.
CONCLUSION
We have developed an advanced DRIE process for
etching ultra high aspect ratio features in silicon. By
ramping the process parameters, including bias power,
step duration, and pressure, we have significantly
increased the achievable aspect ratio for trenches of 1 to
10 µm width. We have shown aspect ratios of 69.8 for a
5.7 µm trench, and up to 97.3 for a 3 µm trench.
Additionally, by ramping the passivation parameters, we
are able to decrease the undercut at the top of the trench to
less than 2 µm for a 5 µm opening. With further
optimization and an improved masking layer, we may be
able to further improve the aspect ratio.
ACKNOWLEDGEMENTS
This work was done in the Lurie Nanofabrication
Facility (LNF), a member of the National
Nanotechnology Infrastructure Network, which is
supported in part by the National Science Foundation.
This project is funded by the MAST Program of the Army
Research Lab (ARL) under Award Number W911NF-08-
2-0004.
REFERENCES
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etching silicon,” U.S. Patent 5501893, Mar. 26, 1996.
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silicon dry etching for microelectromechanical
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1550-1562, 2003.
Etch rate (μm/min)
4
3
2
2.5μm
1
3.5μm
4.4μm
5.3μm
0
0 50 100 150
Time (min)
Figure 7: Etch rate over time for different trench
widths.
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CONTACT
*K. Najafi, tel: +1-734-763-6650; najafi@umich.edu
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