andrew potter upenn - sunfest 2007 · andrew potter upenn - sunfest 2007 oxide etching etch rate...
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Andrew Potter UPenn - SUNFEST 2007
Andrew Potter UPenn - SUNFEST 2007
Modeling and Fabrication of Piezoelectric RF MEMS
ResonatorsAndrew Potter
SUNFEST 2007Final Presentation
Andrew Potter UPenn - SUNFEST 2007
Project Goals
1. Optimize and Characterize ICP Etchinga. Silicon Oxide Etchingb.Aluminum Nitride Etching
2. Simulate the Effects of Non-Ideal Etch Profiles
mrsec.wisc.edu/facilities/trionphantom.jpg
Andrew Potter UPenn - SUNFEST 2007
ICP Characterization
Andrew Potter UPenn - SUNFEST 2007
Fabrication Steps
Oxide
Photo-Resist
PlatinumSilicon
Substrate
AlN
Andrew Potter UPenn - SUNFEST 2007
ICP Characterization
http://www.el-cat.com/images/silicon_etching.gif
θ
Side-Wall Sloping
Layer to Be Etched
Masking Layer
Substrate
Andrew Potter UPenn - SUNFEST 2007
Oxide EtchingEtch Rate vs. RIE Power (SpOx) 50sccm CF4, 100mT, 500W ICP
0
100
200
300
400
500
600
50 100 150 200RIE Power (W)
Etch
Rat
e (n
m/m
in)
Photo ResistOxide
Best Selectivity Recipe:P: 100mT Flow: 50sccmRIE: 50W ICP: 500WSelectivity: 1:3 (Sputtered)
1:4 (PECVD)Oxide Rate: 50nm/min (SpOx)
35nm/min (PECVD)Etchant: CF4Masking Layer: Photo-Resist
Andrew Potter UPenn - SUNFEST 2007
AlN Etching
Recipe Characterization:P: 100mT BCl3: 25sccmCl2: 25sccm Ar: 10sccmRIE: 50W ICP: 500WSelectivity: 4:1 (SpOx)
6:1 (PECVD Ox)AlN Rate: ~200nm/minEtchant: BCl3 Cl2 and ArMasking Layer: Oxide
2um
AlN Etch Profile(SEM Micrograph)
Andrew Potter UPenn - SUNFEST 2007
Modeling and Simulations
Andrew Potter UPenn - SUNFEST 2007
Figures of Merit
Typical Admittance Plot
-85
-80
-75
-70
-65
-60
-55
-50
70 71 72 73 74 75Frequency (Mhz)
Adm
ittan
ce (d
B)
Resonance
Anti-Resonance 12 33 dBdB
res
fffQ−
=
Quality Factor
( )VIY 10log20=
Admittance
⎟⎟⎠
⎞⎜⎜⎝
⎛−
=−
−
resresanti
resantit ff
fk4
22 π
Efficiency
Andrew Potter UPenn - SUNFEST 2007
Simulation MethodsCOMSOL Multiphysics (Piezo Plane-Stress)
Loss Factor Damping (η=1/1000)Applied Voltage Amplitude: 1VppPlatinum Thickness: 200nm
(80% Coverage on Multi-Fingered Devices)
200um
2um
50um
Andrew Potter UPenn - SUNFEST 2007
Mode Shapes
3-Fingered
1-Fingered
5-Fingered
Andrew Potter UPenn - SUNFEST 2007
Frequency Shift vs. Sidewall AngleThree Fingers
228
229
230
231
232
233
234
235
236
40 50 60 70 80 90
Sidewall Angle (deg)
Freq
uenc
y (M
hz)
ResonanceAnti-Resonance
One Finger
69.5
70.0
70.5
71.0
71.5
72.0
72.5
40 50 60 70 80 90Sidewall Slope (degrees)
Freq
uenc
y (M
hz)
ResonanceAnti-Resonance
5-Fingered
374
376
378
380
382
384
386
388
40 50 60 70 80 90Sidewall Angle (degrees)
Freq
uenc
y (M
hz)
resonance anti-resonance
Andrew Potter UPenn - SUNFEST 2007
kt2 vs. Sidewall AngleThree Fingers
1.70%1.80%1.90%2.00%2.10%2.20%2.30%2.40%2.50%2.60%
40 50 60 70 80 90Sidewall Angle (degrees)
kt^2
(per
cent
)
One Finger
1.7%1.8%1.9%2.0%2.1%2.2%2.3%2.4%2.5%2.6%
40 50 60 70 80 90Sidewall Slope (degrees)
kt^2
5 Fingers
1.7%1.8%1.9%2.0%2.1%2.2%2.3%2.4%2.5%2.6%
40 50 60 70 80 90Sidewall Angle (deg)
kt^2
(%)
Andrew Potter UPenn - SUNFEST 2007
What’s Left
1. Optimize ICP Etching a. Oxide Etching – Want Higher Etch Rates
Without Sacrificing Selectivityb.Aluminum Nitride – Try to Optimize
Etching Profile
Andrew Potter UPenn - SUNFEST 2007
Thank you:Adriane, Carlos, Nipun, Rashed, Marcelo
Dr. Gianluca Piazza Dr. Jan Van der Spiegel
NSF