nanofabrication techniques

1. Introduction
to
Nanofabrication

2. Can you find any nano products?

4. Nature’s Nanofabrication
Gecko foot: 14400 hairs (setae) per mm2 . Seta has hundreds
of tiny spatular tips
Gecko
Spatulae
Setae
Lamellae
Foot

5. SEM image of Gecko foot

6. Fruit Fly Foot

7. Diameter of setae-2 diameter of human hair
Each setae end with 1000 tiny tips of 200 nm size
Single setae can lift 20 mg
A million setae can lift 20 Kg
It is discovered that the seta is 10 times more adhesive than predicted from prior
measurement on whole animals. The adhesive is so strong that a single seta can
lift the weight of an ant 200 µN = 20 mg. A million setae could lift the weight of a child
(20kg, 45lbs). A million setae could easily fit onto the area of a Dime. The combined
attraction of a billion spatulae is a thousand times more than a gecko needs to hang
from the ceiling. Maximum potential force of 2,000,000 setae on 4 feet of a gecko =
2,000,000 x 200 micronewton = 400 newton = 40788 grams force, or about 90 lbs!
This is 600 times greater sticking power than friction alone can account for. Weight
of a Tokay gecko is approx. 50 to 150 grams.

8. Microfabricated aligned multiwalled carbon nanotube setae and spatulas.
(A)Optical picture of gecko foot showing that the setae are arranged in
(B)many lobes along the foot. (B) SEM image of natural gecko setae
(C)terminating into thousands of smaller spatulas. (E–H) SEM images
(D)of synthetic setae of width 50 (E), 100 (F), 250 (G), and 500 (H) µm.
(E)(C and D) Side views (C) and higher magnification SEM image
(F)(D) of the 100 µm setae.
Synthetic Gecko type adhesives

9. Synthetic hair.-----------In Spiderman toys
Spiderman toy hangs from glass plate
The 40g toy has gecko tape on hand
0.5cm-square tape should hold 100g and more

10. C-BOT

11. RFID Powder Chip-Smart Dust
Size = 0.05 mm3
Used in:
1. Body implants
2. Currency
3. Product tags
4. Passport identification etc.
Fabricated using
Electron Beam
Lithography (EBL)
Radio Frequency IDentification chip

12. Size Timeframe
10 m 1971-72 Intel 4004 CPU (1971), Intel 8008 CPU (1972)
3 m 1975 (Intel 8085 CPU)
1.5 m 1982 (Intel 80286 CPU)
1 m 1985 (Intel 80386 CPU)
800 nm 1989 (Intel 486 CPU)
600 nm 1994 (Intel 80486DX4 CPU)
350 nm 1995 (Intel Pentium Pro CPU)
250 nm 1998 (Intel Pentium II)
180 nm 1999 (Pentium III)
130 nm 2001 (Intel Tualatin, PIII) Historical----70% scaling down in 2-3 Years
90 nm 2002-03 (Intel, AMD) for CMOS
65 nm 2006 (Pentium 4, Core 2, Pentium D (Texas, Motorola)
for CMOS fabrication (Lattice constant-0.543 nm….100 atoms across)
45 nm End of 2008 by IBM, Intel (next milestone)
32 nm 2009-10, AMD, Intel, uses double patterning and immersion lithography
22 nm 2011-12 (revolutionary)
16 nm Early 2013
? nm or pm

13. Transistor for 90 nm process Influenza virus
Silicon Transistors

14. 90 nm Generation Gate Oxide
1.2 nm SiO2

15. Different Approaches for Nano Fabrication
Top Down
Bottom up

16. Different Approaches for Nano Fabrication
Nature
Self-Organization
Eg. Self-assembly
Lithography
Eg. Surface patterning
Engineering
Technology
Top-down
Bottom-up
Gap
Emerging methods
Eg. Scanning probes
Microcontact printing
Nanoimprint
Nanostencil
1 A°
1 nm
10 nm
100 nm
10 mm
1 mm
100 m
10  m
1 m Bridge

17. Bottom UP
Carbon nanotube synthesis

18. Self assembled Monolayers (SAM)
Self assembled monolayers. Monolayer structures formed by the
spontaneous self-assembly of alkanethiols on metal surfaces.
In SAMs, the thiol groups are bonded covalently to the metal
surface, and the non-covalent, intermolecular packing of the
alkane chains causes the molecules to arrange into an ordered,
two-dimensional crystal or liquid crystal.
ODT-Octadecane thiol –CH3(CH2)17SH

19. STM image 15 nm x 15 nm
Decanethiol Hexagonal array Gold surface
Self Assembled Monolayers (SAM)

20. Lithography
Process for making prints using plates and ink
Greek lithos = "stone"
graphein = "write“
Because the plate was originally a porous stone….

21. Types of Lithography
1. Photo Lithography (Optical, UV, EUV)
2. Soft Lithography
3. Electron Beam Lithography
4. Focused Ion Beam Technology
5. Dip Pen Lithography
6. X-ray Lithography
7. Scanning Probe lithography
8. Interference Lithography
9. Nanoimprint Lithography
10.Selfassembly
11.Nanotemplates
12.Immersion Lithography

22. Soft
Lithography

23. Soft Lithography
Method of fabricating or replicating MICRO and NANO structures
using elastomeric stamps.
Soft material used: PDMS (PolyDiMethyl Siloxanes)
PDMS is also used in:
1. Contact lenses
2. Glass adhesive
3. Breast implants
4. Silicon grease and lubricants
5. Cosmetics (hair, skin)
Material is colorless, inert, cross
Linkable, hydrophobic.

24. Soft Lithography-Types
1.Micro Contact Printing (CP)
2. Replica Moulding (REM)
3. Microtransfer Moulding (TM)
4. Micromoulding in Capillaries (MIMIC)
5. Solvent Assisted MicroMoulding (SAMIM)

25. Stamp Fabrication
1. Desired pattern is etched on silicon using photolithography or
E-Beam Lithography.
2. Pouring the silicon resin over the pattern and degassed.
3. Resin curing (crosslinking) using hardener at 70 C for 24 hr.
4. Remove the stamp from the mould.

27. Stamp Fabrication

28. Microcontact Printing (CP)
1. Inking a stamp. PDMS stamp with pattern
is placed in ethanol and ODT solution.
2. ODT settles down onto the PDMS stamp
3. PDMS stamp with ODT is placed on the
gold substrate to transfer the pattern to
the gold surface.
ODT-Octadecane thiol –CH3(CH2)17SH
Gold (100 nm thickness) layer on glass substrate

29. Y.Xia, G.M. Whitesides et al
Microcontact Printing (CP)

30. CP followed by wet
etching
 Contact Printing
Y.Xia, G.M. Whitesides et al

31. Replica Moulding

32.  Transfer Moulding

33.  Transfer Moulding
Y.Xia, G.M. Whitesides et al

34. Micro Moulding in Capillaries

35. MIMIC
Y.Xia, G.M. Whitesides et al

36. Solvent Assisted Micro Moulding

38. Applications
1. Production of lab on chip systems
2. In biotechnology-biosensors
3. In polymer electronics-LED’s and LCD’s
4. Microreactors
5. Smaller details than photolithography 100 nm
6. In MEMS & NEMS
Optical micrograph of a GaAs/AlGaAs FET
fabricated using MIMIC
Y.Xia, G.M. Whitesides et al
Advantages:
Low cost technique
Can operate in room temp. and pressure
Substrate need not be flat
Conformal patterning is possible

39. Photo-Lithography

40. Positive resist Negative resist
Resist material (Polymer)
Silicon substrate
Light
It is the first and the
earliest microfabrication
technology in
semiconductor industry
……….since 1963…
Photo-Lithography

41. Photoresist Materials
Photo resist materials are photosensitive polymeric material
which undergoes chemical changes on exposure to suitable
wavelength of light.
Positive photoresist: The exposed area to light becomes soluble
to a solvent and the unexposed area remains insoluble to
photoresist developer.
Negative photoresist: The exposed area to light becomes
relatively insoluble to the solvent and the unexposed area can
be dissolved by the photoresist developer.
Eg. SU-8-Epoxy resin (negative)
Used in UV range 400 nm

42. Photoresist materials

43. Photo-Lithography
1. Contact 2. Proximity

44. 3. 1:1 Projection
Avoid mask damage problem or
non uniform exposure problem
Photo-Lithography

45. Reduction Projection
Photo-Lithography

46. Photo-Lithography-Steps
1. Pre-treatment of silicon wafers
2. Coating photoresist
3. Pre-exposure bake
4. Exposure
5. Post exposure bake
6. Development
7. Descum
8. Hard bake
9. Pattern transfer
10.Removal of photoresist
70 nm line and spacing
SEM images
Feature size depends on the
photomask and wavelength
of light used
Still used in high volume production
Photolithography animation

47. MEMS

48. High aspect ratio image, 60 nm lines in
300 nm thick resist

49. Thick SU-8 negative resist pattern,
5, 10, 20 micron on 50 micron film

51. Scanning Probe Lithography

52. Scanning Probe Lithography

53. Two types
Atomic Force Microscopy
&
Scanning Tunneling Microscopy
Scanning Probe Lithography

54. Atomic Force Microscopy
Tip curvature = 10 nm
Usual scanning area= 100 m2
Tips are made out of Si3N4
Scanning Probe Microscopy

55. Atomic Force Microscopy

56. AFM Scribbing

57. AFM Lithography Scratching

58. Nanoindentation and Scratching

59. Tips are brought into contact with a thin polymer film
Bits are written by heating a resistor built into the cantilever
to a temperature of 400 C. The hot tip softens the polymer
and briefly sinks into it, generating an indentation
For reading, the resistor is operated at lower temperature,
300 C. When the tip drops into an indentation, the resistor
is cooled by the resulting better heat transport, and a
measurable change in resistance occurs.
The 1024-tip experiment achieved an aerial density
of 200 Gb/in2
Millipede: Data storage in a polymer

60. Millipede: Data storage in a polymer

61. Millipede: Data storage in a polymer

62. AFM Manipulation of Polystyrene

63. Scanning Tunneling Microscopy
Lithography
Scanning Probe Microscopy

64. STM Lithography
Using SPM for Nano Lithography.flv

65. STM Lithography

66. STM Lithography

67. STM: Manipulation of Atoms
Xe atom on Nickel surface
World’s smallest billboard

68. Electron Beam Lithography

69. E-Beam Lithography
Uses a beam of electrons to generate patterns on a polymer
Surface.
E-beam can beat the diffraction limit of light and make patterns
in nanometer level.
Mainly used in mask making in photolithography, low volume
Production of semiconductor components and R & D.
Time consuming: For one wafer E-beam will take:-10 hrs
Photolithography:- Few min

70. E-Beam Lithography
Electron Optics
Electron gun can be thermionic or field
emission cathode

71. E-Beam Lithography

72. E-Beam Lithography

73. Focused Ion Beam (FIB)
Technology

74. Focused Ion Beam (FIB)
Developed in early 1980’s
Widely used in micro & nanofabrication
Semiconductor industry
Chip design
Used for localized milling and deposition of conductors &
Insulators
Used for trimming of manetoresistive heads in storage disks
Used in MEMS & NEMS
FIB is based on interactions of ion beam with surfaces &
molecules

75. Fabrication of 3D structures

76. Interaction of Ion Beam with Specimen
1. Ion produces radiation damage
2. Ion striking the surface can cause sputtering
3. Can generate secondary electrons-
used for imaging the surface (1-10 electrons
are emitted per ion)
4. Chemical effects (photoresist materials)
secondary
electrons

77. Principles of FIB
1. Ion source
2. Ion column
3. Imaging
4. Milling
5. Deposition
Liquid Metal Ion Source (LMIS)
Al, As, Au, B, Be, Ga, Ge, Pb, P, Pd, Zn
Metal ions
Extractor
Emitter
Liquid metal Reservoir
Metal film
10 m

78. FIB-2.5 nm resolution

79. Typical ion column

80. Dual Beam Configuration

81. Applications of FIB

82. Pattern etched in Cr layer on Si
For fabrication of a waveguide
Applications of FIB

83. Applications of FIB
a. Initial milling to make section
b. Release of bottom and sides
c. Final thinning
d. Section
Sequence of TEM sample preparation using FIB

84. Applications of FIB
Hexagonal holes milled in a Cr layer on Si

85. Cutting vias for device modification
Applications of FIB

86. Applications of FIB
Platinum connects deposited for modification

87. Applications of FIB
Metal lines cut by ion milling for circuit modification

88. Modified device viewed by tilting
Applications of FIB

89. Spintronic nano-ring prototype patterned by
focused ion beam milling
Applications of FIB

90. Applications of FIB
Rapid prototyping: silicon nanostructures realized in two hours,
36 x 36 pillar array (pillar diameter = 280 nm, height = 4 µm)

91. Art of FIB- Logo written in an eye of a fly

92. State of the Art
TEM lamella preparation
Cross sectioning
Failure analysis
Emerging Applications
MEMS device fabrication, modification
Scanning probe microscope tips
Micromedical device structuring
Micro- and Nano-print master fabrication
Arbitrary shapes
Applications of FIB

93. X-Ray Lithography

94. X-Ray Lithography
• Developed in 1970
• Optical lithography is limited by
illumination wavelength
• X-ray rep. the shortest wavelength in the
EM spectrum
• IBM started 0.25 micron VLSI chip in
1995

95. Principles of X-ray lithography
• X-ray wavelength -0.01-10 nm
• X-ray can penetrate the majority of materials
• Only materials with high atomic number can
absorb x-rays
• X-rays cannot be focused because the refractive
index of all materials to x-ray is the same (n=1)
• X-ray lithography can only be 1:1 proximity
lithography

96. Schematic of X-ray lithography
Incident X-rays
Resist
Substrate
Gap G
Absorber mask

97. X-ray lithography mask
• Membrane made of low atomic number
material such as silicon or silicon carbide
with patterned high atomic number
material as absorber (Au,W,Ta)
• Low atomic number materials are
transparent to x-rays

98. X-ray lithography
• For X-rays with 1 nm wavelength
• Silicon membrane is of 1-2 micron thickness
• Absorber thickness is in the range of 300-500
nm
• The exposure depth in resist will be about 1
micron
• Proximity gap is 5-50 micron (PG is required
because of the poor mechanical strength of the
mask, it is very fragile and cannot have any
mechanical contact with the surface

99. X-ray lithography system
1. X-ray source
a. Point x-ray source
b. Synchrotron radiation source (SRS)
2. X-ray maskaligner and stepper
3. X-ray mask
4. X-ray resists

100. Selection of X-ray wavelength
• The thickness of supporting membrane for x-ray
mask
• The thickness of absorber metal
• The resist sensitivity
• The resist thickness
• The x-ray diffraction effect and rage of photon
induced electrons
• The thickness of output window
• The imaging property of particulates on mask
Optimum wavelength of X-ray lithography is 0.7-1 nm

101. ENN 10

106. Dip Pen Lithography (DPN)
ENN-2

107. DPN Process
The tip applied ink molecules diffuse through the water meniscus
and deposit on the surface to form nanostructures

108. • Material should be mobile enough to release from the
AFM tip
• There must be a driving force to initiate the formation of
nanostructures
• Pattern hydrophilic, hydrophobic, ionic, uncharged
materials, high and low molecular weight materials
• Covalent bonding, physical, electrostatic interactions and
electrochemical reactions, polymerizations are used as
the driving force for making the nanostructures
• Driving force depends on the nature of the ink
Dip Pen Lithography

109. Surfaces & Inks
• Gold- Alkanethiol-Covalent bonding
• Silicon,glass-Octadecanethiol-Covalent
• Gold-Mercaptohexadecanoic acid
• SiO2/GaAs-hexamethyldisilazine
• Polypyrole/polyaniline

110. Lateral force microscopy
images
a. ODT dot
b. MHA dots
c. ODT dot array
d. ODT grid

111. Multiple ink nanostructures generated by DPN. The white lines
are MHA patterns, and the darker surroundings background is ODT
ODT
(Octadecane trichlorosilane)
MHA
(Gold-Mercaptohexadecanoic acid)

112. LFM images of a. SPAN; b. PPy patterns. Topographic images
of c. SPAN array With cross-section d. PPy lines with cross-section

113. Topographic image of Au nanostructures forming the letters DU

114. Mobile precursor molecules are transported from the tip to the
surface, where they are reduced or oxidized to produce immobile
nanostructures
Electrochemical-DPN

115. Elemental
nanostructures
by E-DPN
a. Ag Line
b. Ge Line
c. Pd Line
d. Cu square

116. 32 Pen array fabricated for
multipen DPN

117. Summary-DPN
• DPN is a flexible nanofabrication
technique
• Experimentally simple
• Extraordinarily powerful
• Patterning of SAMs, polymers, organic,
inorganic materials, biological, metallic,
semiconducting & insulating materials

118. Micro and Nano fabrication -Uses
1. Micro & Nano electro mechanical systems (MEMS & NEMS)
2. Semiconductor industry (VLSI)
3. Display industry, LCD and LED
4. Security features
5. Biochips
6. High density magnetic storage
7. Optoelectronics
8. Nanoelectronics
9. Sensors
10.Micro reactors etc.
Virtual Microscope