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Patterning of nanometer-scale cantilevers integrated in CMOS circuit by e-beam lithography

María Villarroya, Gemma Rius*, Jaume Verd, Jordi Teva, Gabriel Abadal, Eduard Figueras*, Jaume Esteve*, Núria Barniol and Francesc Pérez-Murano*

Departament d’Enginyeria Electrònica. Escola Tècnica Superior d’Enginyeria. UniversitatAutónoma de Barcelona.08193 Bellaterra (Spain)

*Institut de Microelectrónica de Barcelona (CNM-CSIC).Campus UAB.08193.Bellaterra (Spain)Maria.Villarroya@uab.es, Gemma.Rius@cnm.es

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Outline1. Introduction: Nanoelectromechanical System

for mass detection: ― Working principle― Resolution― Readout system

2. Fabrication process for optical lithography― CMOS process― Transducer definition: Post CMOS process― Optical lithography defined cantilevers

3. EBL defined cantilevers:– Fabrication process– Results

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1. Introduction: Nanoelectromechanical System for mass detection

http://www.uab.es/nanomass/

NANOMASS IST 2001-33068: Nanoelectromechanical systems with CMOS circuits Integration on the same substrate of CMOS circuits and nanomechanical structures

Nanomechanical structure (sensing/actuating)

+ CMOS circuit (Amplification and signal processing)

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Principle of a mass sensor based on a resonatingnanocantilever

effo m

kfπ21

=o

oo

o

eff ffkf

fm

m δπ

δδ 32212 =−≈

fresm- δ- δfres- δf m+ mδ

1,36 1,38 1,40 1,42 1,44 1,46 1,48

1,0

2,0

3,0

4,0

5,0

6,0

7,0

Mód

ulo

corr

ient

e (n

A)

Frecuencia (MHz)

-80

-60

-40

-20

0

20

40

60

80

100

Fase

cor

rient

e (g

rado

s)

1,36 1,38 1,40 1,42 1,44 1,46 1,48

1,0

2,0

3,0

4,0

5,0

6,0

7,0

Mód

ulo

corr

ient

e (n

A)

Frecuencia (MHz)

-80

-60

-40

-20

0

20

40

60

80

100

Fase

cor

rient

e (g

rado

s)

1,36 1,38 1,40 1,42 1,44 1,46 1,48

1,0

2,0

3,0

4,0

5,0

6,0

7,0

Mód

ulo

corr

ient

e (n

A)

Frecuencia (MHz)

-80

-60

-40

-20

0

20

40

60

80

100

Fase

cor

rient

e (g

rado

s)

1,36 1,38 1,40 1,42 1,44 1,46 1,48

1,0

2,0

3,0

4,0

5,0

6,0

7,0

Mód

ulo

corr

ient

e (n

A)

Frecuencia (MHz)

-80

-60

-40

-20

0

20

40

60

80

100

Fase

cor

rient

e (g

rado

s)

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(N/m) 4 3

3

ltwEk ⋅

⋅= (Hz) 21

2lwfo ρπ

Ε=

)/( 10·83.0)/( 7.50 333 HzgrtlHzgrfk

fm

o

≈=δδ

E =Young modulus, ρ=density

Elastic constant Resonance Frequency

Resolution

2.8·10-13

8.4·10-9

meff (g)

4.2·10-191.4 MHz0.020.10.510Nano

4.9·10-14364 kHz44430125Micro

Sensitivity(g/Hz)fok (N/m)t (µm)W (µm)l (µm)Cantilever

For Silicon Cantilevers

Hemoglobin protein mass: 1.09·10-19 g

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By Electrostatic excitation and electrical detection

Cantilever resonance frequency measure

Electrode located very close to the cantilever

Translation of mechanical signal into electrical signal

( )tcV

tVC

tcVV

tVcCVC

ttI DC

ACoACDC

ACoC ∂

∂+

∂∂

≈∂∂

++∂

∂+=

∂∂

= )()(·)(tx

xc

tc

∂∂

∂∂

=∂∂

VdcVac

-+

Ic(t)

Co

CIRCUIT

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Outline1. Introduction: Nanoelectromechanical System for mass

detection: ― Working principle― Resolution― Readout system

2. Fabrication process for optical lithography― CMOS process― Transducer definition: Post CMOS process― Optical lithography defined cantilevers

3. EBL defined cantilevers:– Fabrication process– Results

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2. Fabrication Process for optical lithography defined cantilevers

• STANDARD CMOS CNM25 2P,2M

• ONE POLYSILICON LAYER IS USED AS STRUCTURAL LAYER

• SIO2 IS USED AS SACRIFICIAL LAYER

• MECHANICAL TRANSDUCER DEFINED AFTER CMOS AS A POST PROCESS:

• OPTICAL LITHOGRAPHY• E-BEAM LITHOGRAPHY

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Mechanical transducer definition process by optical lithography

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CMOS circuit with microcantilevers

w= 1 µml=50 µmt=600 nm

fo=567 kHzδm/ δf = 248.9 ag/Hz

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Electrical Characterization

490k 500k 510k 520k 530k 540k

-4,0m

-2,0m

0,0

2,0m

4,0m

6,0m

8,0m

10,0m

Mag

nitu

de (V

)Frequency (Hz)

-6

-5

-4

-3

-2

-1

0

1

Pha

se (d

eg)

Cantilever #1 Cantilever #2

Cantilever resonance has been measured simultaneously on two cantileversCantilever 1 f0,dc=18V = 501 kHzCantilever 2 f0,dc=18V = 512 kHz

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Outline1. Introduction: Nanoelectromechanical System

for mass detection: ― Working principle― Resolution― Readout system

2. Fabrication process for optical lithography― CMOS process― Transducer definition: Post CMOS process― Optical lithography defined cantilevers

3. EBL defined cantilevers:– Fabrication process– Results

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Development

3. Cantilever definition process by EBL

pmma

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E-beam characteristics

• SEM based EBL Equipment: model LEO 1530

• Low energy: 3keV* (dose : 30 µC/cm2)

• CMOS wafer present a sharp topography: Al pre-contacts have been defined

• Positioning/alignment of e-beam

AlPre-contacts* F. Campabadal, S. G. Nilsson, G. Rius, E.Figueras and J.Esteve. CDE-05

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PROCESS RESULTS STEP by STEP

E-beam pattern on pmma

Al pattern after lift-off

After RIE Release cantilevers

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200nm wide, 30 µm long cantileversδm/ δf = 13 ag/Hz

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