andrew potter upenn - sunfest 2007 · andrew potter upenn - sunfest 2007 oxide etching etch rate...

Andrew Potter UPenn - SUNFEST 2007


Modeling and Fabrication of Piezoelectric RF MEMS

ResonatorsAndrew Potter

SUNFEST 2007Final Presentation


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


ICP Characterization


Fabrication Steps

Oxide

Photo-Resist

PlatinumSilicon

Substrate

AlN


ICP Characterization

http://www.el-cat.com/images/silicon_etching.gif

θ

Side-Wall Sloping

Layer to Be Etched

Masking Layer

Substrate


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


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)


Modeling and Simulations


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


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


Mode Shapes

3-Fingered

1-Fingered

5-Fingered


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


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

(%)


What’s Left

1. Optimize ICP Etching a. Oxide Etching – Want Higher Etch Rates

Without Sacrificing Selectivityb.Aluminum Nitride – Try to Optimize

Etching Profile


Thank you:Adriane, Carlos, Nipun, Rashed, Marcelo

Dr. Gianluca Piazza Dr. Jan Van der Spiegel

NSF

andrew potter upenn - sunfest 2007 · andrew potter upenn - sunfest 2007 oxide etching etch rate...

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