Top-Down Nanomanufacturing David T. Shaw State University of New York at Buffalo.

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Top-Down Nanomanufacturing David T. Shaw State University of New York at Buffalo

Transcript of Top-Down Nanomanufacturing David T. Shaw State University of New York at Buffalo.

Page 1: Top-Down Nanomanufacturing David T. Shaw State University of New York at Buffalo.

Top-Down Nanomanufacturing

David T. Shaw

State University of New York at Buffalo

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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

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Overview

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How Do You Naomanufacture?

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Top-down Fabrication for Moore’s Law of Miniaturization

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Lithography, although imperfect, can generate complex 3-D nanostructures

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Top-down Processing is reaching a Limit

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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

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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

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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.

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Top-down Fabricating Nanowires With Alternating Diameters or Compositions

(ii) Generation of PR pattern

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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)

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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)

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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.

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Future Integrated Nano-Systems

Bottom-up (sensors, memories, etc.) will be integrated with top-down nanocomponents

C. Sun, X. Zhang UC Berkeley

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Top – Down Nanomanufacturing

Derived directly from the chip-making processes

Single Silicon Crystal Growth

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Vacuum Basics

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Vacuum Basics

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Mean Free Path

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Vacuum Circuit

Liu, UCD Phy250-2, 2006

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Pumping Speed

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Conductance of a Straight Tube

Liu, UCD Phy250-2, 2006

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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

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Vacuum Measurements

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Photolithography Basics

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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.

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Diminishing Lithographic Wavelengths

E. Chen, Harvard

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Optical Lithography

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Comparison of Three Lithographic Systems

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Contact and Proximity Printing

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Mask Aligners

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Mask Alignment

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Contact Lithography Advantages

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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

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Projection Printing (Stepper)

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Projection Printing (Stepper)

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Projection Lithography Advantages

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Projection Lithography Disadvantages

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Exposure Tools

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Phase Shift Mask (PSM) Lithography

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Optical Proximity Correction

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Surface Reflections and Standing Waves

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Phase Shift Mask (PSM)

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Immersion Lithography

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X-ray Lithography

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X-Ray Lithography (XRL)

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X-Ray Lithography (XRL)

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X-Ray Photomask

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EUV Lithography

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Nano-Imprint Lithography

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Dip Pen Nanolithography

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Focused Ion Beam Lithography

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Electron Beam Lithography

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Optical vs. E-Beam Lithography

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E-Beam Lithography

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Electron Beam Lithography

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Electron Beam Lithography

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EBL nanostructures

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E – beam Nanoelectromechanical (NEMS) Structures

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Thin Film Deposition

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Thin Film Deposition -- Sputtering

• High purity sputtering gas necessary – Typically 0.1mtorr – 10 mtorr

• Short mean free path

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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

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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

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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

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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.

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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

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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

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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

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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

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Magnetron Guns

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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

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Vacuum Evaporation

• Target material is heated to melting point

• Atoms leave target as vapor

• Vacuum allows atoms to go directly to substrate

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E-Beam Evaporation

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Etching

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Pattern Transfer

R. B. Darling

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Basic Etching Concepts

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Chemical Etching

R. B. Darling

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Physical Etching

R. B. Darling

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Ion Enhanced Etching

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Ion Enhanced Etching

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Parallel Plate Etchers

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Sputter Etching and Ion Milling

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Positive Ion Beam Milling