Mikheil Mebonia PhD student at Ilia State, RWTH Aachen Universities and Forschungszentrum Jülich.

Electronic and thermoelectric properties of nanograiting layers

presented at 6-th Georgian-German School and Workshop in Basic Science (GGSWBS’ 14), July 2014, Tbilisi, Georgia

Advisors : Raphael Hermann (FZJ, University of Liege), Larissa Juschkin (FZJ, RWHT Aachen University ), Avtandil Tavkhelidze (Ilia State University)

When it happens ?

There will be two reflected waves. One reflected from the top of the indent and another from the bottom of the indent. If the depth a=λ/4 , where λ is electron de Broglie wavelength, two reflected waves will interfere destructively resulting in no reflected wave.

Nanograting (NG) improves thermoelectric and electron emission properties when the grating pitch becomes comparable with the electron’s de Broglie wavelength

Density of state (DOS) of nanograting layer

)(ρ0 EDOS in plane layer DOS in nanograting layer )ρ(E

where, G (H,w,a)>1 is a geometry factor.

Z

GEE /)(ρ)ρ( 0

Geometry induced doping or G-doping

Electron concentration n in the CB increases, which can be termed as geometry-induced electron doping or G-doping.

There are no ionized impurities.

G-doping is T-independent

J. Simon, V. Protasenko, C. Lian, H. Xing and D. Jena, , Science 327, 60-64 (2010).B. Yu, M. Zebarjadi, H. Wang, K. Lukas, H. Wang, D. Wang, C. Opeil, M. Dresselhaus, G. Chen, and Z. Ren, , Nano Lett. 12, 2077 (2012).

Process flow

Interference lithography

• Large-area periodic structures

• Large depth of focus

• Requires a coherent light

• Low cost – no complicated and expensive optics

• Ultimate resolution (half-pitch) for the wavelength ~λ/4

EUV: l = 11 nm feature size: ~3 nm

Possible scheme for IL

q1q2

S S‘

Resolution is limited by l/(sinq1+sinq2), max l/2.

No mask needed.

Lloyd mirror

• Ultimate resolution (half-pitch) for the wavelength ~λ/4

EUV LABORATORY EXPOSURE TOOLTechnical Specifications

Cleanroom class 100 (ISO 3) environment

Illumination scheme interference lithography

Accepts up to 100 mm wafer

Max. exposable area: 65 x 65 mm2

Single field: 2 x 2 mm2

EUV sensitive CCD camera

High precision positioners on all axes (encoder resolution < 10 nm)

Dose monitor for λ = 13.5 nm

LABORATORY-SCALED EUV SOURCESpectral Range and Technical Specifications

Pinch Radius 100 µm

Radiance: L ~ 100 W/(mm2sr) @ λ = 10,9 nm with 3,2% bandwidth

Electron/ion densities: n ~ 1017 cm−3

Temperature of plasma: Te ~ 35 eV Coherence length: lcoh ≈ 10-25 µm Triggered source >> repetition rate: up to 1,5

kHz

Gas Discharge Plasma Source for EUV Generation

PowerSupply

energystorage

f = j X B

I

switch

EXPERIMENTAL SETEUV Laboratory Exposure Tool

EUV Sourc

e

Dose Monito

r

Lithography Chamber

Loadlock

CCD Camer

a

Capacitive

Sensors

Mask holder and

Lithography Mask

Wafer holder

insid

e

EXPERIMENTAL SET-UPEUV Laboratory Exposure Tool

RIE facility in Physikzentrum

Reactive Ion Etcher Sentech SI 591 1M2

(SF6, CHF3, CF4, CH4, H2, N2)

Evacuated chamber

Etch gases flow in

Electrodes at top and bottom

Ionised gas

Adsorbed electrons create voltage drop from ion cloud to wafer

Ions are accelerated towards wafer

Review - Reactive Ion Etching

Review - Reactive Ion EtchingIon energy

pressure

Different etching mechanisms in Reactive Ion Etching

Physical (sputtering)

Chemical

Ion-assisted

We measure temperature and magnetic field dependence of• Resistivity • Thermal conductivity • Seebeck coefficient

Use van der Pauw technique 4 pont method to measure resistivity

Conclusion

* Make nanograiting on SOI wafer using XUV -IL

* Do ion etching

* Use CCMS to measure electrical and thermoelectric property

* Use AFM (Atomic force microscopy), scanning electron microscope (SEM) and ellipsometrie to measure properties of structured SOI wafer

* Different size of transmission mask to get less pitch size of structure

Thanks for your Attention!