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Top-Down Nanomanufacturing
David T. Shaw
State University of New York at Buffalo
Contents
• Process Overview
• Lithography
– Vacuum basics
– Photolithography basics
– Photomasks
– Exposure Tools
– X-ray lithography
– Immersion lithography
– Nano-imprint lithography
– Other techniques - Dip pen, AFM, FIB
– Electron Beam lithography
• Thin Film Deposition
• Etching
Overview
How Do You Naomanufacture?
Top-down Fabrication for Moore’s Law of Miniaturization
Lithography, although imperfect,
can generate complex 3-D nanostructures
Top-down Processing is reaching a Limit
Brief History of Chip Making Based
on Photonic Lithographic Fabrication
Photonics lithographic fab is driven by electronics
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1947 - First transistor invented at Bell by Bardeen, Brattain and
Shockley
1958 - First integrated circuit at Texas Instruments by Jack Kilby
1959 – Planar technology on Si substrate using SiO2 as insulation
layers
More than three decades of exponential miniaturization in sizes and
costs based on a top-down processing
Dimensions move into nanoscale range at the beginning of the 21st
century
Top-down technology is facing three fundamental design limits:
– Transistor scalability
– Performance
– Power dissipation
Top-down Nanostructures
• Top down fabrication can be likened to sculpting from a block of stone.
– A piece of the base material is gradually eroded
until the desired shape is achieved, i.e., you start
at the top of the blank piece and work your way
down removing material from where it is not
required.
• Nanotechnology techniques for top down fabrication vary but can be split into physical and
chemical fabrication techniques
Top-down Fabrication of Nanodots
Stacking Ge nano–islands on Si(001) (a) AFM image and
(b) cross sectional TEM of a typical Ge/Si heterostructure.
G. Capellini elat, Appl. Phys. Lett. 82, (2003) 1772-1774
Top-down Fabricating Nanowires With Alternating
Diameters or Compositions
(ii) Generation
of PR pattern
Top-down Fabricating Nanowires
With Alternating Compositions
• Preparing an array of GaAs wires with a triangular
cross section from a GaAs(100) wafer patterned
with mask stripes along the (011) direction and
anisotropically etched in an aqueous solution,
• Patterning the resultant wire array (after removal of
the etch mask stripes) with photoresist lines
perpendicular to the orientation of the GaAs wires,
• Etching the GaAs wires using the photoresist as a
mask to generate wires with alternating widths, or
• Depositing metals through the
photoresist pattern to create
GaAs wires with segments
alternating in composition.
Y. Sun et al, Small,1(11)1052(2005)
Combining top-down and bottom-up
A lamellar-forming block copolymer on 2D surfaces
chemically patterned with a square array of spots
form 3D bicontinuous morphologies.
K. C. Daoulas et al, PRL,96,036104(2006)
Integration of Top-down and Bottom-up nanomanufacturing
Integrated multifunctional nano-assembly onto bio-MEM devices
and lead to scalable and cost effective nanomanufacturing
X. Zhang et al, Journal of Nanoparticle Research 6: 125–130, 2004.
Future Integrated Nano-Systems
Bottom-up (sensors, memories, etc.) will be integrated with
top-down nanocomponents
C. Sun, X. Zhang
UC Berkeley
Top – Down Nanomanufacturing
Derived directly from the chip-making processes
Single Silicon
Crystal Growth
Vacuum Basics
Vacuum Basics
Mean Free Path
Vacuum Circuit
Liu, UCD Phy250-2, 2006
Pumping Speed
Conductance of a Straight Tube
Liu, UCD Phy250-2, 2006
Outgassing rates for common materials
(millibar-liter/sec-cm2)
Common vacuum materials
Construction Materials which are compatible with UHV
OFHC copper, Be-Cu alloy, phosphor bronze, 304 SS, 310 series SS, 340 SS (magnetic),
Teflon, MACOR (machinable glass composite), 6061 Al (essentially pure aluminum), 2024
Al (harder alloy), quartz, Pyrex (gassy), alumina (careful with glazed ceramics),
molybdenum, tungsten "mu-metal" magnetic shielding (Co, Ni, Fe), polyimide (Vespel), SnAg solder
Construction Materials which are compatible with UHV
Zn, Cd--Especially be careful of fasteners and bolts, brass, certain solders
Vacuum Measurements
Photolithography Basics
Photolithograpy
• The most important part of top down fabrication technique is
nanolithography.
– In this process, required material is protected by a mask and the
exposed material is etched away.
– Depending upon the level of resolution required for features in
the final product, etching of the base material can be done
chemically using acids or physically using ultraviolet light, xrays or electron beams.
• This is the technique applied to the manufacture of computer
chips.
Diminishing Lithographic Wavelengths
E. Chen, Harvard
Optical Lithography
Comparison of Three Lithographic Systems
Contact and Proximity Printing
Mask Aligners
Mask Alignment
Contact Lithography Advantages
Contact Lithography Disadvantages
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Good contact difficult to achieve
Sensitive to particular contaminants
Hard to get below 2µm
DUV requires quartz mask
Alignment can be difficult
Projection Printing (Stepper)
Projection Printing (Stepper)
Projection Lithography Advantages
Projection Lithography Disadvantages
Exposure Tools
Phase Shift Mask (PSM) Lithography
Optical Proximity Correction
Surface Reflections and Standing Waves
Phase Shift Mask (PSM)
Immersion Lithography
X-ray Lithography
X-Ray Lithography (XRL)
X-Ray Lithography (XRL)
X-Ray Photomask
EUV Lithography
Nano-Imprint Lithography
Dip Pen Nanolithography
Focused Ion Beam Lithography
Electron Beam Lithography
Optical vs. E-Beam Lithography
E-Beam Lithography
Electron Beam Lithography
Electron Beam Lithography
EBL nanostructures
E – beam Nanoelectromechanical (NEMS) Structures
Thin Film Deposition
Thin Film Deposition -- Sputtering
• High purity sputtering gas necessary
– Typically 0.1mtorr – 10 mtorr
• Short mean free path
Sputter Deposition
• Magnetron sputtering is the most widely used method
for etching and thin film deposition.
• Although the basic diode sputtering method (without
magnetron or magnetic enhanced) is still used in
some application areas, magnetron sputtering now
serves over 90% of the market for sputter deposition.
• Magnetron sputtering can be used to coat or dry etching virtually any solid materials .
Ref: www.gencoa.com
Sputtering System
http://www.teercoatings.co.uk
A typical sputtering
system consists of a
vacuum chamber with
substrate holders and
magnetron guns,
vacuum pumps and
gauging, a gas supply
system, power supplies and a computer
control system.
The Magnetron
A Magnetron is comprised of :
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www.gencoa.com
A CATHODE = electron source,
An ANODE = electron collector, and
A combined electric & magnetic field = B X E
Microscopic View of Sputtering
The impact of an atom or ion
on a surface produces sputtering from the surface as a
result of the momentum
transfer from the incoming
particle. Unlike many other
vapor phase techniques
there is no melting of the
material.
www.gencoa.com
The Magnetron Gun
www.teercoatings.co.uk
• A magnetron consists of a target with magnets
arranged behind it to make a magnetic trap for charged particles,
such as argon ions, in front of the target.
• Atoms are knocked out of the target surface by the ions. These
sputtered atoms aren’t charged negatively or positively, so they
go straight out of the magnetic trap to coat the substrate.
The Magnetron Plasma
• Confinement between a negatively biased target and closed
magnetic field produces a dense plasma.
• High densities of ions are generated within the confined plasma, and
these ions are subsequently attracted to the negatively biased target,
producing sputtering at high rates.
ref: www.gencoa.com
Target Erosion
• Target erosion is greatest where the magnetic field and the subsequent plasma density is greatest.
• This leads to inefficient use of target material, particularly in the
case of ferromagnetic targets.
www.gencoa.com
Sputtering Insulators
• For an insulator target, the ions bombarding the target will
create charging, and the electric field necessary to maintain
a plasma is greatly diminished.
• To alleviate this problem, an RF power supply is used to
generate the electric field.
www.gencoa.com
Magnetron Guns
The Latest in UHV Sputtering
http://www.ajaint.com
• A UHV, magnetron sputter source that fits through the port of
a 2.75" CF flange complete with its tilt gimbals assembly.
• This revolutionary new design is true UHV - all ceramic to
metal construction.
Vacuum Evaporation
• Target material is
heated to melting
point
• Atoms leave target
as vapor
• Vacuum allows
atoms to go directly
to substrate
E-Beam Evaporation
Etching
Pattern Transfer
R. B. Darling
Basic Etching Concepts
Chemical Etching
R. B. Darling
Physical Etching
R. B. Darling
Ion Enhanced Etching
Ion Enhanced Etching
Parallel Plate Etchers
Sputter Etching and Ion Milling
Positive Ion Beam Milling