Technic and Fabrication of Lithography

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Technic and Fabrication of Lithography

X-Ray lithography dan E-beam lithography

Mochamad Zakki Fahmi, ^Ph.D

Department of Chemistry, Airlangga University

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Syntesis of Nanoparticle

Litrography

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Lithography

• Lithography (from Ancient Greek λίθος, lithos, meaning 'stone', and γράφειν, graphein, meaning 'to write') is a method of printing originally based on the immiscibility of oil and water.

• For nano class well-known as nanolitography

Nanolitography

Optical Lithography

Electron beam Lithography

Multi photon

lithography Xray

lithography

Scaning Probe Lithography

lithographyAFM

Dip pen Lithography Nanoimprented

ithography

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OU NanoLab/NSF NUE/Bumm & Johnson

Microcontact Printing

(Soft Lithography)

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For un-flat Litography

• Production of silicon integrated circuits

• Patterning biological

macromolecules, organic and inorganic salts, colloidal

materials, conducting polymers, polymer beads

• The figure to the right is a patterned rod

Image courtesy of Jackman et al, Science 1998. vol. 280(5372) pp 2089-2091

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Motivation:

Novel Example

• Transferring micrometer size pattern onto various surfaces

– Surface does not have to be flat (as opposed to photolithography)

– The figure to the right is an example of how one would transfer patterns to a cylindrical rod

Image courtesy of Jackman et al, Science 1998. vol. 280(5372) pp 2089-2091

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History

• Both lithography and stamp printing have been around for centuries

– It was the combination of the two that gave rise to microcontact printing

• In 1993, Amit Kumar and George M. Whitesides developed microcontact printing at Harvard University

• Subsequent methods of soft lithography have since been explored

• In 1996 IBM began research on improving optical lithography in order to enhance the precision of the printing process

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Process Schematic

Image taken from http://www.aip.org/tip/INPHFA/vol-8/iss-4/p16.pdf

A prepolymer (2) covering the master (1) is cured by heat or light and

demolded to form an elastomeric stamp (3), which is inked by immersion (4) or with an ink pad (5) and printed onto the substrate (6), forming a self- assembled

monolayer, which is transferred into the substrate by a selective etch.

Scanning electron micrographs show the master, image of the stamp, and the printed and etched pattern.

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Photomask

• Create desired pattern on computer (AutoCAD, Adobe Illustrator, or your favorite graphics program)

• Print onto transparency

• Further reduction of size can done photographically

• Pattern must be in solid black and white and

printed using an opaque ink, which is determined by the photoresist

opaque

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About the Photomask:

Snowflake

• The snowflakes in the photomask are made such that each subsequent one was half the size of the

previous one

• Measurements were made

regarding snowflake size as well as distance between the snowflakes

– These measurements were used to evaluate how well the pattern transfer occurred

• The depth of the stamp was determined (determined by the master):

– If the stamp is too shallow, there can be contact in between the features – If the stamp is too deep, the features

can be distorted

11.3 mm

9.175 mm

From Whitesides et. al paper 0.629 mm

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About the Photomask: "I Love Nanolab"

• In this photomask, “I Love Nanolab” the largest text (#1) are 3mm by 21.3 mm.

Each subsequent set is half the size of the previous.

• The smallest size (#8) is 128 times smaller than the biggest size, and is 23.4µm X 166.4µm

21.3 mm 3 mm

Don’t YOU love NanoLab?

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About the Photomask: OU Logo

• In this photomask, the largest OU logo is 10 mm wide and 13.7 mm long.

10 mm

13.7 mm

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Stamp Master (mold)

• Done on glass slide using the mask as the source of the pattern

• Apply photoresist (10-20 μm)

– (MicroChem SU-8 2010) Spin coat for even distribution

• Cover Sample with Mask and Expose to UV light

– The resist will harden upon exposure (negative resist)

• Soft-Baking

– Put on hotplate, or oven for 3 minutes

• Develop

– Unexposed resist will be dissolved, while the exposed resist remains

• Wash Master and clean up

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The Stamp

• Clean master sample and place in walled container (disposable petri dish).

• Pour silicone resin evenly over master

– The silicone resin is liquid polydimethylsiloxane [PDMS]

• Bake the PDMS to solidify (65C for 15-20h).

• Remove cured stamp from master and wash both in EtOH

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Chemistry of the Process

• Stamp is inked with a thiol (R-S-H)

• The thiol ink pattern is stamped onto the metal surface

• The thiol ink works as an etch resist

• Etching removes metal on uninked areas

• A thiol ink is ~2mM solution of hexadecanethiol

• The substrate is a Pd or Au thin film evaporated on polished Si wafer

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Transferring the Pattern to a Thin Metal Film

• Wash both substrate (the metal) and the stamp in EtOH

• Using Q-Tip, coat the stamp with the thiol solution and dry it

• dry under N

₂

stream for ~30sec

• Bring stamp into contact with substrate for 10

sec., remove stamp and dry substrate under N

₂

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Useful Chemistry

• The sulfur atoms bonds to the metal ^{(Pd or Au)}

• The carbon chains of the thiol will then align with each other to create a hydrophobic SAM

(self-assembling monolayer)

• The monolayer acts as a protective coating against the etchant

– The best results are often obtained by the longest chains because they create a larger and therefore better barrier

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Etching the Substrate

• Immerse substrate in diluted (1:3) etchant for <30 sec (Pd Etchant, type TFP in CYANIDE!!! – be careful, it’s highly toxic!)

• The time here is very important!!! If you leave it too long in the etch, you will most likely remove ALL the Pd, if it’s not long enough, then your pattern will not be fully developed.

• Remove from etchant and immediately quench it in deionized water, rinse and dry.

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