top-down and bottom-up processes presented by: steven price april 11, 2006 ee 518 pennsylvania state...
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Top-down and Bottom-up ProcessesTop-down and Bottom-up Processes
Presented by: Steven PriceApril 11, 2006
EE 518
Pennsylvania State University
Instructor: Dr. J. Ruzyllo
Outline of PresentationOutline of Presentation
Top-down approach Bottom-up approach Why will it be needed? Applications Challenges of Bottom-up processing The future of top-down and bottom-up processing Summary
Top-Down ApproachTop-Down Approach
Uses the traditional methods to pattern a bulk wafer as in EE 418 lab.
Is limited by the resolution of lithography.
http://pages.unibas.ch/phys-meso/Education/Projektstudien/Lithographie/Litho-M1-Lithography.html
What Constitutes a Top-down What Constitutes a Top-down Process?Process?
Adding a layer of material over the entire wafer and patterning that layer through photolithography.
Patterning bulk silicon by etching away certain areas.
www.nanoscience.at/ aboutnano_en.html
Current Top-down TechnologyCurrent Top-down Technology
Use of 193 excimer laser with phase shift masks to for features 65 nm in size.
Phase shift masks and complex optics are used to achieve this resolution.
http://www.lrsm.upenn.edu/~frenchrh/lithography.htm
193 nm ArF excimer laser photolithography stepper
Problems with the Top-down Problems with the Top-down ProcessProcess
Cost of new machines and clean room environments grows exponentially with newer technologies.
Physical limits of photolithography are becoming a problem.
With smaller geometries and conventional materials, heat dissipation is a problem.
http://www.cit.gu.edu.au/~s55086/qucomp/gifs/intro.moore1.gif
Bottom-Up ApproachBottom-Up Approach
The opposite of the top-down approach.
Instead of taking material away to make structures, the bottom-up approach selectively adds atoms to create structures.http://idol.union.edu/~malekis/ESC24/KoskywebModules/sa_topd.htm
The Ideas Behind the Bottom-The Ideas Behind the Bottom-up Approachup Approach
Nature uses the bottom up approach.– Cells– Crystals– Humans
Chemistry and biology can help to assemble and control growth.
http://www.csacs.mcgill.ca/selfassembly.htm
Top-down Versus Bottom-upTop-down Versus Bottom-up
Etched wafer with desired pattern
Apply layer of photoresist
Expose wafer with UV light through mask and
etch wafer
Start with bulk wafer
Top Down Process Bottom Up Process
Start with bulk wafer
Alter area of wafer where structure is to be created by
adding polymer or seed crystals or other
techniques.
Grow or assemble the structure on the area
determined by the seed crystals or polymer. (self
assembly)
Similar results can be obtained through bottom-up and top-down processes
Why is Bottom-Up Processing Why is Bottom-Up Processing Needed?Needed?
Allows smaller geometries than photolithography. Certain structures such as Carbon Nanotubes and
Si nanowires are grown through a bottom-up process.
New technologies such as organic semiconductors employ bottom-up processes to pattern them.
Can make formation of films and structures much easier.
Is more economical than top-down in that it does not waste material to etching.
Self AssemblySelf Assembly
The principle behind bottom-up processing.Self assembly is the coordinated action of
independent entities to produce larger, ordered structures or achieve a desired shape.
Found in nature.Start on the atomic scale.
Applications of Bottom-Up Applications of Bottom-Up ProcessingProcessing
Self-organizing deposition of silicon nanodots.
Formation of Nanowires. Nanotube transistor. Self-assembled
monolayers. Carbon nanotube
interconnects.
http://web.ics.purdue.edu/~mmaschma/bias_image_gallery1.htm
Self-organizing Deposition of Self-organizing Deposition of Silicon Nanodots.Silicon Nanodots.
Most common applications are in optical devices and memory.
Silicon nanodots are deposited onto silicon dioxide with no need for lithographic patterning.http://www.iht.rwth-aachen.de/en/Forschung/nano/bottomup/deposition.php
Making NanodotsMaking Nanodots
Process for making nanodots
1. Apply layer of self-assembled polymer film.
2. Grow layer of desired material to create nanodot.
Polymer template for nanodot
65 billion nanodots per square cmhttp://news.bbc.co.uk/1/hi/sci/tech/33010241.stm
NanodotsNanodots
Each nanodot can hold one bit of information.
10 Trillion dots per square inch.
13 nm high
80 nm wide
Self Assembled Nanodots
http://physics.nist.gov/Divisions/Div841/Gp3/Projects/Atom/atom_dots_proj.html
Properties of Carbon Properties of Carbon NanotubesNanotubes
Stronger than steel Multiple tubes slide inside
of each other with minimal effects of friction.
Electrical current density 1000 times greater than silver or copper.
Can range from having metallic properties to semiconductor properties based on it’s configuration.
http://en.wikipedia.org/wiki/Nanotubes
Types of Carbon NanotubesTypes of Carbon Nanotubes
metallic
http://www.tipmagazine.com/tip/INPHFA/vol-10/iss-1/p24.html
Semimetallic and semiconducting
Growing Carbon NanotubesGrowing Carbon Nanotubes
Deposit few particles of Iron (most common) to act as catalyst.
Apply a hot environment of carbon containing gas (typically CH4)
The particle catalyzes the decomposition of the gas and carbon dissolves in the particle.
When the particle is supersaturated with carbon, it extrudes the excess carbon in the form of a tube.
http://www.phys.hawaii.edu/~sattler/Archives/archives91-94Apr7-2.htm
Nanotube TransistorNanotube Transistor
Basic diagram for a nanotube transistor
Benefits of transistor over conventional designs:– Smaller– Faster– Less material used– Many of the problems
associated with conventional devices are solved
www.nanotech-now.com/ news.cgi?story_id=06788
Nanotube Transistor-self Nanotube Transistor-self AssembledAssembled
www-drecam.cea.fr/.../ LEMautoassemblage.html
Diagram of Nanotube transistor
Carbon Nanotube
SiO2
Ti/Au Contact
AFM Image
Amine silane
Nanotube Transistor Nanotube Transistor Construction by DNAConstruction by DNA
DNA strands connect to gold electrodes on top of silicon.
DNA strands connect to ends of carbon nanotube.
Silicon and nanotubes are mixed and the DNA makes the connections to form nanotube transistors.
http://www.trnmag.com/Photos/
2004/121504/DNA%20makes%20nanotube%20transistors%20Image.html
Problem With Carbon Problem With Carbon Nanotube TransistorsNanotube Transistors
Interface between metal electrodes and carbon nanotube is very sensitive.
Changing just one atom can significantly affect transistor performance.
Self-assembling nanotubes is not efficient.
Growing nanotubes in place has had little success.
http://www.thomas-swan.co.uk/pages/nano_images.html
Self-assembled Monolayers Self-assembled Monolayers (SAMS)(SAMS)
Molecules are deposited molecule-by-molecule to form a self-assembled monolayer.
Creates a high quality layer of material.
Layers are deposited one layer at a time.
http://www.mtl.kyoto-u.ac.jp/english/laboratory/nanoscopic/nanoscopic.htm
MonolayersMonolayers
Organic molecules can’t be deposited using extreme conditions because it would damage the organic molecules.
SAMS technique does not damage organic molecules.
SAMS films are nearly defect free.
Used to deposit organic semiconductors.http://www.orfid.com/images/img-vofet1.gif
Carbon Nanowire Carbon Nanowire InterconnectsInterconnects
Metal contact acts as a catalyst to promote one-dimensional crystal growth.
Can one day be implemented as interconnects.
Silicon Nanowire Diameter <1nm
http://www.iht.rwth-aachen.de/en/Forschung/nano/bottomup/nanowires.php
Nanotube Interconnect ProcessNanotube Interconnect Process
http://www.nasa.gov/centers/ames/research/technology-onepagers/carbon_nanotubes_vertical.html
Benefits and Challenges of Benefits and Challenges of Nanotube InterconnectsNanotube Interconnects
Can have a much greater conductivity than copper.
Is more heat resistant than copper.
Carries a much larger current than copper.
Orientation of carbon nanotubes remains a problem.
Technology is not reliable enough to be used in device manufacturing.
http://www.nasa.gov/centers/ames/research/technology-onepagers/carbon_nanotubes_vertical.html
Carbon nanotubes grown on a metal contact through
PECVD.
Carbon nanotubes after layer of silicon dioxide
added.
Challenges for the Bottom-Up Challenges for the Bottom-Up ApproachApproach
Making sure that the structures grow and assemble in the correct way.
Forming complex patterns and structures using self assembly.
Contamination has a significant impact on devices with such small geometries.
Fabricating robust structures.
Strategies for Bottom-Up Strategies for Bottom-Up ProcessingProcessing
Combination of top-down and bottom-up processes to simplify construction.
Use catalysts and stresses to achieve more one-directional growth.
http://www.isnm2005.org/_metacanvas/attach_handler.uhtml?attach_id=296&content_type=application/pdf&filename=Paper%2036.pdf
Future of Top-down and Future of Top-down and Bottom-Up ProcessingBottom-Up Processing
http://www.imec.be/wwwinter/business/nanotechnology.pdf
Advancements Made so FarAdvancements Made so Far
Carbon nanotube transistor (Stanford U.)
Organic monolayers for organic transistor (Yale U.)
Nanotube based circuit constructed (IBM)
Nanomotors and gears created (NASA)
http://snf.stanford.edu/Education/Nanotechnology.SNF.ppt
What to Look ForWhat to Look For
Vias and interconnects being implemented with carbon nanotubes.
Nanotube transistors replacing conventional designs.
SAMS being used to create organic semiconductor based devices.
Carbon nanotubes becoming more and more prevalent as their growth is controlled.
http://www.engin.brown.edu/Faculty/Xu/
Nanotube array possibly used in future televisions.
ConclusionConclusion
Top-down processing has been and will be the dominant process in semiconductor manufacturing.
Newer technologies such as nanotubes and organic semiconductors will require a bottom-up approach for processing.
Self-assembly eliminates the need for photolithography.
Bottom-up processing will become more and more prevalent in semiconductor manufacturing.