top-down nanomanufacturing david t. shaw state university of new york at buffalo
TRANSCRIPT
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• 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 sculpt-ing 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 fab-rication vary but can be split into physical and chemical fabrication techniques
Top-down Fabrication of Nanodots
G. Capellini elat, Appl. Phys. Lett. 82, (2003) 1772-1774
Stacking Ge nano–islands on Si(001) (a) AFM image and (b) cross sectional TEM of a typical Ge/Si heterostructure.
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), Sn-Ag 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, x-rays 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
• 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 etch-ing virtually any solid materials .
Ref: www.gencoa.com
Sputtering System
A typical sputtering system consists of a vacuum chamber with substrate holders and magnetron guns, vacuum pumps and gauging, a gas supply system, power sup- plies and a computer control system. http://www.teercoatings.co.uk
The Magnetron
A Magnetron is comprised of :• A CATHODE = electron source,
• An ANODE = electron collector, and
• A combined electric & magnetic field = B X E
www.gencoa.com
Microscopic View of Sputtering
www.gencoa.com
The impact of an atom or ion on a surface produces sput-tering 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.
The Magnetron Gun
• 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.
www.teercoatings.co.uk
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 sub-sequent 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
• 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.
http://www.ajaint.com
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