MNC 2013, Nov. 6, 2013, Sapporo
6C-3-2Development of Electron Projection Lithographyusing Wafer-Size nc-Si Surface Electron Emitter
A. Kojima,a,b N. Ikegami,b H. Ohyi,a N. Koshida,b and M. Esashica Crestec Corp., Hachioji, Tokyo, Japanb Tokyo Univ. of Agri. & Tech., Koganei, Tokyo, Japanc Tohoku Univ., Sendai, Japan*This study is supported by Funding Program for WorldLeading Innovative R&D on Science and Technology

Background and Purpose
Massively parallel EBL system is attractive for advanced lithography⇒ Key issue: development of emitter which meets the requirements.
We have developed nanocrystalline Si (nc-Si) ballistic cold cathode:Appl. Surf. Sci. 146, 371 (1999)(1) Uniform, Energetic, Directional, and Planar emission.
(2) Capability of high speed switching with a low driving voltage.
(3) Small energy dispersion of emitted electrons.
These features are compatible with Massively Parallel exposure:
JVST B 31, 06F703 (2013)This work
・ Fabrication of a 4”-diam nc-Si emitter with patterned emission windows.
・ Evaluation of the emission characteristics including the uniformity.
・ Application to 1:1 electron projection lithography.
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nc-Si surface electron emitter & ballistic emission mechanism

Emitter structure and TEM image of nc-Si dots
Model of ballistic hot electron
generation and emission:
Appl. Phys. Lett. 98, 062104 (2011)
Nonequilibrium
When a positive bias voltage is applied to thesurface electrode with respect to the substrate,electrons are accelerated by cascade tunnelingwithout suffering serious energy loss.

Output electron energy distribution: Appl.
Phys. Lett. 81, 2472 (2002)

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Features and Possible Applications
nc-Si emitter

Conventional FED

Energy5 ～7 eV~ kTAngle

Directional

Dispersive

ModeSurface

PointMedia

Vacuum, Air, Solutions

only in High vacuum☆ Vacuum : Flat Panel Display (SID, 2004)
Parallel EB Lithography (JVST, 2008)
Night Image Pick-up (JVST, 2008)☆ Gases: Negative Ion Source (Air) (JVST, 2007)
VUV Emission (Xe) (JVST, 2009)☆ Solutions : H2 generation and pH control (APL, 2007)
Thin Films (EESL, 2010; APL, 2013)*Evaluation of the electron emission characteristics in the large area of the emitter
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EB Projection Lithography using Wafer-Size nc-Si Surface Emitter(Surface Electron Emission Lithography)
Emission
Area mask

Magnet1

Pulsed bias
voltagenc-Si

nc-Si
Small
angle dispersion
Accelerating
voltage＝5.0 kV

3mmmaskAu/Ti
B＝0.56T
ResistTarget wafer

Stage

Target wafer

Magnet2

The electron beam through the window of thepatterned mask strikes the resist on the target.
⇒ Replica of the pattern

The vacuum chamber with
anti-vibration mountResolution : R = rwDt = sv Dt = sv [sv /(eE/m)] = m sv2/eE
sv: deviation of initial electron velocity
5Fabrication Process of Wafer-Size nc-Si Surface Electron Emitter
1. Poly-Si layer deposited on n++Si substrate(The surface was polished by CMP)

2. Anodization to form nc-Si layer
W Lamp
HF+C H OH
2100 nm5

3. Electrochemical Oxidation of nc-Si layer
Ethylene glycol +H2O

SEM Image of the cross-section ofthe nanocrystalline Si(nc-Si) Layer

nc-Siwafer
4. Resist coating & patterning(EB direct writing or photolithography)
Resist(⇒mask)

mask

5. Surface Electrode deposition with RF sputter

poly-Si

Au/Ti(Emission Area)

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Observed 4”-emission image on fluorescence screen

Vd=15VThe surrounding ring-shaped pad apply
voltage to the surface electrode uniformly.

*The emission current of about 400uA was obtained with Vd of 15V.

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Confirmation of the emission uniformity

20VA

Z stage 2

Ie

Insulator

Only the electrons which passthrough the aperture reach thecollector, and generate Ie.

MagnetAperture Plate
t0.5mm X stage

Collector

Settingto 3mm

Y stage

Magnet (Φ80mm)

Insulator

AZ stage 3

Vd

Insulator

Id

Z stage 1

Electron Emitter*Measurement of themagnetic field intensity
on four position.

32160mm
460mmPositionMagnetic Field (T)

10.56

20.56

30.54

40.54

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Electron Emission Characteristics at 4 points on the emitter:
04C

3CC

432C

1-2

1-2-7

102Emission current density Ie(A/cm )101010-4-410-6-610-8

32 1

210log(Ie/Vd )2

Diode current density Id(A/cm )

10

10

2

10-6

0

10-860mm

460mm

10-9

10-8

10-10-10

10-505101015

Applied Voltage (V)10-100.06

0.08

0.1

0.12

0.14

0.16

1/VdIV & Emission

FN PlotThe variation of the amount of emission
current among the points under theapplied voltage of 15V was about 30%.

FN plot :Linear ⇒ The electron istransported by the FN type tunnel
effect inside a nanosilicon layer.

9Exposure Results 1: Large pattern (3um～16mm)(Investigation of exposure property)
AA

Surface Electron emitter

Target Wafer exposed by the emitterLine width:10um, Wavelength:5um
ZEP520A :t80nm
Exposure time :0.5s
Estimated Electron dose:
25mC/cm2
Acc. Voltage:5kV・Uniform and Low-distortion exposure

Exposed pattern of the micron order・This emitter can expose patterns of various
sizes on whole wafer simultaneously
10Wafer-size emitter to expose fine pattern over the target wafer(Investigation of exposure property)
Emitter(Φ4inch)

Emitter Arraync-Si

32mask

160mm
4poly-Si
60mm

Emitter array createdon four positions.

100nm
100nm

Configuration of the emitter array
Each emitter array correspond to theemission area where the emission
current was measured previously.

200nm
One of 5×5 Emitter Array*The microscopic structures of the nc-Si areobserved in the rectangular emission region.
11Exposure Results 2: Fine pattern (100nm square dot & space)(Investigation of exposure property)

200nm

3200nm
124200nm

ZEP520A :t80nm
Exposure time :0.5s
Electron dose(at position
1):25mC/cm2
Acc. Voltage:5kV

200nm
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Summary・Dot & space patterns of 100 nm ~ 1000 μm were
exposed in parallel over a large area using 4”-diamnc-Si planar ballistic cold cathode.
・Due to energetic, directional, and uniform emission,
this effect is potentially useful for direct one-shotprojection of nano-micro patterns on the target.

Future Work・ Device fabrication for improvement in resolution
toward 10 nm.

・ Development of direct projection EB lithography
over a further enlarged surface area.
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Acknowledgement
This work is granted by JSPS through First Program initiated by
the Council for Science and Technology, and supported byNanotechnology Platform of MEXT, Japan, at the Center for
Integrated Nanotechnology Support, Tohoku University.

Thank you for your attention.

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