Advanced Manufacturing

Choices

ENGR 165- 265Spring 2014, Dr. Lawrence

Kulinsky

Scanning Proximal Probe Lithography

• Electrical field of a Scanning Proximal Probe to modify substrate region directly under the tip

• Mechanical methods where Atomic Force Microscope (AFM) tip directly affects the substrate via scraping, thermal deformation or material transfer (such as dip-pen lithography (DPL))

• Near-Field Scanning Optical Microscopy

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• From Rayleigh equation with, = 193nm, NA = 0.93 and k1 = 0.25 or

• There are technical challenges and financial constraints facing F2 157 nm system

• E-beam and ion beam lithography can be used to achieve better resolution, but even these system suffer from deficiencies such as proximal effects

Photolithography in Distress

Scanning Tunneling Microscope

• Invented in 1981 by Gerd Binnig and Heinrich Rohrer (at IBM Zurich) – Nobel Prize in Physics (1986)

• Small (< 1 m) probe is scanned over sample’s surface with typical separation of 3 to 10 Angstroms

• Piezoelectric control of the tip’s z position• Close proximity of the tip and the surface atoms

allows for electron tunneling across the gap between the tip and the surface

• Tunneling current is very sensitive to changes in the gap distance – the current falls by factor of 10 with the gap increase of 1 Angstrom

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Tunneling Quantum Effect

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Scanning Tunneling Microscope

• Small bias is used – 10 mV to 2

V

• Two modes of operation:– Constant

current– Constant

height

6http://en.wikipedia.org/wiki/Scanning_tunneling_microscope

Scanning Tunneling Microscope

• Resolution of STM is determined by the sharpness of the tip

• Tungsten tips are etched electrochemically

• Practical STMs’ lateral resolution – 2 Angstroms

• This resolution is more than 1000 times better than the diffraction limit of optical systems

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http://meso.phys.northwestern.edu/research/low-temperature-scanning-probe-microscopy

Scanning Tunneling Microscope

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Scanning Tunneling Microscopy image of graphite, acquired under ambient conditions. Measured at the Dept. for Earth and Environmental Sciences, LMU and Center for NanoScience (CeNS), Munich

STM images of Si (111) plane. http://www.specs.de/cms

Atomic Force Microscope

• Major extension of STM – Atomic Force Microscope (AFM), also known as Scanning Force Microscope (SFM) can be used on conducting or insulating surfaces

• Invented in 1986 by Gerd Binnig, Christoph Gerber, and Calvin F. Quate

• The first commercial AFM was build in 1989• Measures the force between a sharp (Si or

Si3N4) probe and the sample

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SEM picture of the AFM cantilever about 30 m wide. http://en.wikipedia.org/wiki/Atomic_force_microscopy

Atomic Force Microscope

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http://files.campus.edublogs.org/blog.nus.edu.sg/dist/3/2069/files/2012/03/afm-r3jgkw.gif

Main AFM Techniques• Contact Mode

– Tip slides across the surface– Provides highest resolution, but may damage

the surface

• Non-contact Mode– An oscillating tip is scanned 1 to 10 nm above

the sample’s surface– Surface forces (capillary, electrostatic) affect

tips’ resonant frequency

• Tapping Mode (Most Commonly Used)– Similar to Non-contact, but at the largest

deflection the tip touches (taps) the surface, improving resolution vs Non-contact mode

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AFM’s Atomic Resolution

12http://www.eng.utah.edu/~lzang/images/Lecture_10_AFM.pdf

AFM’s Atomic Resolution

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AFM scans of gold structures sputtered for 75, 200 and 400 s on glass substrate before (RT) and after annealing (300C). The average surface roughness in given in nm. V. Švorčík, O. Kvítek, O. Lyutakov, J. Siegel, Z. Kolská, “Annealing of Sputtered Gold Nano-Structures”. Appl. Phys. A 102747751 (2011)

Comparison of STM and AFM

• STM works on conductive samples, while AFM can work on both, conductive samples and insulators

• STM measures tunneling current, AFM measures forces• STM is non-contact, while AFM’s probe often makes a

direct contacts with the sample’s surface• STM works in high vacuum, AFM can operate in liquid

and gas environment• STM and AFM have comparable resolutions• AFM has been adopted on a much wider scale than STM

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Other Proximal Probe Microscopes

• Recently more local scanning probe tools have been developed where their resolution does not depend on the diffraction limit of conventional microscopy

• These probes include:– STMs– AFMs– Scanning Electrochemical Microscopes (SECMS)– Scanning Thermal Microscopes– Scanning Capacitance Microscopes– Magnetic Force Microscopes– Scanning pH probes

• Proximal Probes Can Be Used For Surface Modification– Proximal Lithography

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Electrical Field-Induced Chemical Modification: Oxidation

• Upon the application of small bias (typically between 2V and 20 V) an electrochemical oxidation take place under the proximal probe – can be applied to semiconductors and metals

• This oxide can be used to pattern the substrate in several ways:– Oxide can be used as a mask to etch the

unprotected substrate– In forming the oxide, some of the

substrate material was converted to the oxide (i.e. Silicon Silicon Oxide), so removing the resulting oxide will leave the groove where the oxide used to be

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Top: AFM-tip-induced oxide pattern on Si (100). Tip bias −10 V. Bottom: After etching the oxide for 15 s using 50:1 aqueous HF solution. Ph. Avouris, R. Martel, T. Hertel, R. Sandstrom, “AFM-tip-induced and current-induced local oxidation of silicon and metals”, Appl. Phys. A 66, S659–S667 (1998)

Electrical Field-Induced Chemical Modification: Self-Assembled Monolayer Resist Desorption• Au(111) substrate is coated with

a self-assembled n-alkanethiol ultrathin (~2.5 nm) monolayer (SAM)

• The resist was etched by an STM tip, producing 60 nm x 60 nm wells

17Claudia B. Ross, Li Sun, and Richard M. Crooks, Langmuir 1993, 9, 632-636

Electrical Field-Induced Chemical Modification:

Multilayered Resist System• Multilayered resist allows for translation of SAM

patterning to a more robust oxide mask to produce 50 nm lateral features

• Octadecylsilyl SAM 2 nm thick• Amorphous Si – conductive layer• Si etch tetramethylammonium hydroxide• Si Oxide Etch HF

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Hiroyuki Sugimura, Osamu Takai, and Nobuyuki Nakagiri, Journal of Vacuum Science & Technology B 17, 1605 (1999)

Scanning Probe Lithography vs E-beam

Lithography• Both systems capable of

producing sub-50 nm features• SPL is more tolerant to

exposure variations• SPL uses lower energy and

thus has lower backscattering• Use of ultrasharp (< 10 nm

tip) emitters [CNTs, molibdenum, etc.] can allow for more focused beam, larger gap separation and higher writing speeds for SPL

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K. Wilder, C. F. Quate, B. Singh, and D. F. Kyser, “Electron beam and scanning probe lithography: A comparison”, Journal of Vacuum Science & Technology B 166 (1998)�

Scanning Probe Lithography: Sub 10 nm

lateral resolution

• C-Methylcalix [4]resorcinarene (C-MC4R) molecular resist

• Writing speed 1-10 m/s

20Marcus Kaestnera and Ivo W. Rangelow, “Scanning proximal probe lithography for sub-10 nm resolution on calix[4]resorcinarene”, Journal of Vacuum Science & Technology B 29, 06FD02 (2011)

Scanning Probe Lithography: Sub 10 nm

lateral resolution

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Marcus Kaestnera and Ivo W. Rangelow, “Scanning proximal probe lithography for sub-10 nm resolution on calix[4]resorcinarene”, Journal of Vacuum Science & Technology B 29, 06FD02 (2011)

Mechanical Proximal Probe Methods: Scratch

Lithography• AFM tip is ploughed over

the surface of the substrate

• Features as small as 20 nm are possible

• Possible to use SAM resists to increase resolution

• Tips wear and break• Heated tips can be used to

soften polymer surface for patterning 22

AFM phase image (right) of nanolithographically etched polycarbonate, 5µm scan of Pablo Picasso’s "Don Quixote“ (www.asylumresearch.com)

Mechanical Proximal Probe Methods: Scratch

Lithography

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Xiaohong Jiang et al., “Nanopatterning on silicon surface using atomic force microscopy with diamond-like carbon (DLC)-coated Si probe”, Nanoscale Research Letters, 6:518 (2011)

• Nanopatterning on silicon surface using AFM

• 21 nm lateral resolution is achieved

Mechanosynthesis• Strong electric field (~2V/Å) in the vicinity of the

probe tip allow for sliding atoms over the surface (parallel processes) and picking and placing atoms (perpendicular processes)

• In November 1989 Don Eigler and his IBM Almaden Research Center teammates spelled tiniest IBM logo with 35 Xe atoms on Ni (110) surface.

24researcher.ibm.com

Mechanosynthesis

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Mechanosynthesis• Besides Xe on Ni, CO on Pt, Pt and Pt, Au

on NiAl, Ag on Au surface and few other systems have been successfully demonstrated

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4 Pt atoms spaced on Pt(111) surface and 7 Pt atoms crowded together. From Joseph A. Stroscio; D. M. Eigler, “Atomic and Molecular Manipulation with the Scanning Tunneling Microscope”Science, 254(5036), 1319-1326 (1991)

OU logo and “smiley” produced via STM manipulation of Ag atoms on Au substrate. Saw-Wai Hla, “Scanning tunneling microscopy single atom/molecule manipulation and its application to nanoscience and technology”, Journal of Vacuum Science & Technology B 23, 1351 (2005)

Major Drawback of Proximal Probe Lithography: “Are We

There Yet?”• It took researchers 1 week to position 35

atoms of Xe on Ni substrate• How long will it take to create 10 micron

long, 1 micron wide, 0.5 micron high line (approximately 1016 atoms) if the assembly proceeds at a similar pace?

• The answer: More than 5,000 Billion Years. For comparison, the age of the Universe is less than 4 Billion Years

• We need massively parallel processes to create anything from the bottom up 27

IBM’s Millipede System• Prototype of

IBM storage Millipede data storage device had 4,000 AFM tips for storing and reading data on a plastic substrate

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From E. Gnecco, “Nanotechnology: A gentle jackhammer”, Nature 461, 178-179 (2009).Scale bar is 40 microns

Dip Pen Nanolithography (DPN)

• Invented by Chad Mirkin (Northwestern University) in 1999.

• Water accumulates on AFM tip and creeps onto surface, reducing resolution of AFM measurements

• We can use “inks” on AFM tip to write spots and lines on the surface

• Lines as thin as 15 nm

29Richard D. Piner, et al., "Dip-Pen" Nanolithography, Science 283, 661 (1999)

Dip Pen Nanolithography

• Organic ink used most often with DPL – 1-octadecanethiol (ODT) on gold

• Many different inks/substrates combinations are possible

• Resolution depends on grain size of the substrate, contact time/writing speed, humidity,

• It’s feasible to integrate microfluidic technology for wetting the tips

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30 nm wide ODT line. Richard D. Piner, et al., "Dip-Pen" Nanolithography, Science 283, 661 (1999)

Dip Pen Nanolithography:

Massively Parallel Pen Array• To offset the drawback

of slow processing of DPL the massively parallel 55,000 tip array has been constructed.

• The complete patterning took less than 30 min.

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Top: Section of 55,000 tip array.Bottom: AFM image of a miniaturized replica of the face of the five-cent coin generated by depositing 1-octadecanethiol on a gold-on-SiOx substrate followed with chemical etching. The background is an optical micrograph of a representative region of the substrate on which the approximately 55,000 duplicates were generated. From: ACS Nano, 1(2), 79–83 (2007)

DPN: Protein Nanoarray Construction

• DPN can be used to construct protein nanoarray with several types of proteins on the same array (proof-of-concept study – lysozyme (Lyz) and rabbit immunoglobulin-gamma (IgG)).

• Startup NanoInk commercializes DPN technology

32Ki-Bum Lee, Jung-Hyurk Lim, and Chad A. Mirkin, “Protein Nanostructures Formed via Direct-Write Dip-Pen Nanolithography”, J. Am. Chem. Soc., 125, 5588-5589 (2003)

Thermal DPN (tDPN)

• Developed by William King (Georgia Tech) and Lloyd Whitman (Naval Research Lab)

• Use solid inks – limit evaporation and run-off of the ink, result in sharper features

• Use heated tips and inks such as octadecylphosphonic acid that melts around 100C

• Can be used in vacuum environment (thus compatible with conventional semiconductor manufacturing)

33P. E. Sheehan, L. J. Whitman, William P. King, and Brent A. Nelson, “Nanoscale deposition of solid inks via thermal dip pen nanolithography”, Appl. Phys. Lett. 85, 1589 (2004)

Near-Field Scanning Optical Microscope (NSOM)

• Optical microscopy has a number of advantages (non-destructive, fast, reliable, low-cost, etc.)

• Abbe’s diffraction limit is around 200 nm (while a resolution that is typically achieved with conventional optical microscopy is lower)

• Near-field optical microscopy (probe-surface separation of a few nanometers) can achieve resolution of 30 nm

• Optical glass fiber is pulled, tapered and coated on the sides with Al

• The idea was first voiced by E. H. Singe in 1928 and demonstrated in 1972 by Ash and Nichols (microwave spectrum) and in 1984 by D. W. Poole and colleagues (in the visible spectrum)

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Near-Field Scanning Optical Microscope

35http://www.olympusmicro.com/primer/techniques/nearfield/

High-resolution NSOM micrograph of a 3O-nm Ta film with lOO-nm holes. Dörig, Pohl, and Rohner, J. Appl. Phys., Vol. 59, No. 10, 15 May 1986

Apertureless Near-Field Scanning Optical

Microscope(ANSOM)

• Use sharp tip to scatter oblique incident light

• The main limit to resolution is the sharpness of the tip

• Resolution of up to 10 nm has been achieved

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10 m by 10 m ANSOM micrograph of the 20 nm high waveguide from Gomez et. al., “Apertureless scanning near-field optical microscopy: a comparison between homodyne and heterodyne approaches”, J. Opt. Soc. Am. B, 23 (5), 2006

L. Novotny and S. J. Stranick, “Near-Field Optical Microscopy andSpectroscopy with Pointed Probes”, Annu. Rev. Phys. Chem. 57:303–31 (2006)

•Questions ?

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