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