Nanotechnology, micro and nano fabrication - Hickman

Physicist Richard Feynman - December 29, 1959.

An emerging area of science which studies materials that have very small dimensions.

Scientists of chemistry, biology and physics are studying very small things in order to better understand our world. Nanoscience is the study of objects which are anywhere from hundreds to tens of nanometers in size.

Increases making surface forces more important.

Isomorphically.

Scalled down with all dimenions of the system decreased uniformly.

Surface.

Mass, heat capacity

Pressure, buoyand force, heat flux

The surface to volume ratio of an elephant is smaller than a bug.

True. Think flux (J/m^2)

As objects shrink isomorphically, surface to volume ratio increases.

Surface forces have larger importance/role such as heat loss. Time constants for actions decrease.

Tru.e

Metals, plastic polymers

DNA, nanotubes.

Eletric motors, pneumatic actuators, smart materials, batteries

ATPase, VPL Motor, DNA

• Springs
• Beta-pleated sheets

Gears, Belts, Chains etc

VPL Platforms, DNA double crossover molecules

True. It spins to line up and funnel DNA.

Micro-electro-mechanical-systems. Does not have to be electrical and/or mechanical in broad terms.

microfabricated micron-sized sensors and actuators.

Miniaturized sensors, actuators, and subsystems fabricated by the use of lithography and/or other precision techniques.

This would include MOEMS, BioMEMS, RF-MEMS, m-TAS, Lab-on-a-chip

• A portfolio of techniques and processes to design and create miniature systems.
• A physical product dedicated for a certain final application
• A way of making things: Functions of sensing and actuation with computation and communication to locally control physical paramters at the microscale, yet cause effects at much larger scales.

Accelerometer, gyroscope, blood pressure sensors, digital mirror displays

The number of transisors on a microprocessor would double approximately every 18 months.

• Substrates
• Semiconductor: Si, Ge, GaAs, GaP
• Insulator: glass, quartz, polymers

• Structural: Polysilicon
• Electrical: Conductors and insulators
• Functional: Active materials

• Silicon.
• 1) Slicing
• 2) Lapping and etching
• 3) thickness sorting and flatness measurement
• 4) Chemical mechanical polishing
• 5) Quality inspection (electrical, dimensional)

• Deposition processes (physical deposition; chemical deposition)
• Patterning (Lithography, Diamond Patterning)
• Etching processes (Wet Etching, Dry Etching)
• Micromachining (Bulk micromachining, surface micromachining)

Physical and chemical deposition result in growth in the z-direction.

Chemical deposition includes Chemical Vapor Deposition (CVD) and chemical reactions exploit the chemical reactions for creation of solid materials.

Physical deposition includes Physical Vapor Deposition (PVD) which includes materials physically being deposited onto the structure such as vaporized materials.

Lithography and Diamond Patterning. Restrictions in x-y plane.

Lithography in MEMS context is typically the transfer of a pattern into a photosensitive material by selective exposure to a radiation source such as light. A photosensitive material is a material that experiences a change in its physical properties when exposed to a radiation source. If a photosensitive material is selectively exposed to radiation (e.g. by masking some of the radiation) the pattern of the radiation on the material is transferred to the material exposed, as the properties of the exposed and unexposed regions differs.

Wet and Dry etching.

• Wet etching the material is dissolved when immersed in a chemical solution.
• Dry etching the material is sputtered or dissolved using reactive ions or a vapor phase etchant

Micromachining.

Bulk machining - Structures are made of single crystal silicon, typically by wet or dry etching (subtractive process)

Surface micromachining - Structures are made of deposited or grown layers on top of the substrate, by thin-film deposition. (Additive process)

• Photolithyography = "light" + "stone" + "writing"
• Pattern definition process in micromachining
• Generation and transfer of patterns by the use of exposing radiation through a mask or without a mask
• Visible light, UV, x-ray, E-beam, ion beam
• Optical lithography; photolithography - formation of image with visible or ultraviolet radiation in a photoresist using contact, proximity, or projection printing.

365 nm

10 nm

1nm

• 0.004 nm
• Practically ~1nm

• Small wavelength, diffraction effects may be eliminated. 1nm
• Opaque areas on the mask cast shadows onto the wafter below
• Electron impact source, plasma heated source and synchrotron used
• Mask is dfficult to make and expensive: SiC, Si3N4, Al2O3 and Si with Gold are commonly used
• Good contrast but poor sensitivity of PR
• Limited PR: PMMA

• Lithographie (lithography)
• Galvanik (electroplating)
• Abformung (molding)

Used for lithography, usually x-ray from synchrotron is used

• Create 3D structure as thick as bulk
• micromachined devices while retaining the same degree of design freedom as surface micromachining

• Gear wheels for a dentist's drill bit or Swiss watches
• Nozzles
• Lenses and mirrors for micro-sprectrometers

Electron beam lithography.

• Higher resolution than optical lithography because of small wavelength of 10-50 keV electrons
• Resolution not limited by diffraction but by electron scattering
• Throughput is much less than optical lithography because of serial pattern generation
• Widely used for mask making - not actual device fabrication.

EBL - electron beam lithography because of the lower throughput

• Ions are used as the beam rather than electrons in EBL.
• Higher resolution because of less scattering - electrons can scatter within material upon impact
• Need high energy
• Electrostatic lens has higher aberrations; small aperture and small scan field used
• low throughput

Scanning Probe Lithography

• Atomic scale writing process based on scanning tunneling microscope (STM)
• A typical STM has sub-angstrom vertical resolution and sub-nano lateral resolution
• + use of low electron energy (<100eV) compared to EBL (10-100keV)
• - Low throughput

Dip pen nanolithography

• Use of AFM tip as a "nib", a solid-state substrate (au) as "paper" and molecules with a chemical affinity for the solid-state substrate as "ink"
• Molecules are transported via capillary action (water meniscus) from the AFM tip to the solid substrate then self-assembled.

"ink"s include thiol groups

Soft lithography

• Transfer of ink from a relief structure to a target surface.
• Fabricate chemical patterns with micronscale resolution on surfaces
• demonstrated with molecular monolayer of the thiol molecules on gold surface
• Versatile technology showing high potential for MEMS
• Deformation and distortion of master mold

• Relief printing
• Seals
• Movable type metal printing press
• Gutenberg metal pytopgraphy
• Intaglie printing
• lithographic and xerographic printing
• screen or stencil printing
• ink jet printing

Nano imprint lithography

A technique to generate nano-structures in hard polymers by pressing a rigid master into a thin thermoplastic polymer film that is heated to the glass transition temperature.

The temperature which hard/brittle materials such as polymers transition to a rubber like material for deformation.

NIL uses this for the imprints

• 1) Press in mold.
• 2) Heat up mold and substrate
• 3) Mold separation after cooling
• 4) O2 RIE

• 1) Hydroxylated quartz substrate
• 2) Silane treatment -> convalent link terminated with photoactive molecules
• 3) Photolithography generates deprotected link
• 4) Nucleotide coupling

• 1) thin film deposition
• 500 nm of low stres nitride
• 1 um of oxide

• 2) patterning and RIE of nitride
• Contact photolith + 15 min RIE

• 3) HF undercut of nitride
• (49% for 20 min)

• 4) KOH (25% for 20 min)
• Immediately following the HF H2O rinse

5) crital point drying

• Isotropic - no preference
• Directional - crystal planes
• Vertical - anisotropic

True.

Silica particles (60 nm) with a fluorescent dye are coated with a enzyme specific to O157:H7 E. coli strain

A single bacterium can be detected in 20 minutes

True.

• Extremely strong materials
• Good thermal conductivity
• Metals or semiconductors

Possible use for nano-electronic and nano-mechanical devices (ie nano-wires of field-effect transistors)