A top down approach to network architecture prresentation by sergiohurtadog

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									      Top-down and Bottom-up Processes




          Presented by:        Steven Price
                       April 11, 2006

           EE 518
Pennsylvania State University
  Instructor: Dr. J. Ruzyllo
        Outline 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 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
        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 Technology
       193 nm ArF excimer laser
       photolithography stepper                        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
    Problems with the Top-down
             Process
   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 Approach
                                                                  The opposite of the
                                                                   top-down approach.
                                                                  Instead of taking
                                                                   material away to make
                                                                   structures, the bottom-
                                                                   up approach
                                                                   selectively adds atoms
http://idol.union.edu/~malekis/ESC24/KoskywebModules/sa_topd.htm
                                                                   to create structures.
The Ideas Behind the Bottom-
        up 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-up
Top Down Process                            Bottom Up Process

                                                           Start with bulk wafer
                    Start with bulk wafer


                      Apply layer of                       Alter area of wafer where
                       photoresist                        structure is to be created by
                                                            adding polymer or seed
                                                                crystals or other
                   Expose wafer with UV                           techniques.
                   light through mask and
                          etch wafer
                                                            Grow or assemble the
                                                            structure on the area
                                                           determined by the seed
                                                             crystals or polymer.
                     Etched wafer with
                                                               (self assembly)
                      desired pattern

Similar results can be obtained through bottom-up and top-down processes
Why is Bottom-Up Processing
         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 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
            Processing
   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
                Silicon Nanodots.
                                                                         Most common
                                                                          applications are in
                                                                          optical devices and
                                                                          memory.
                                                                         Silicon nanodots are
                                                                          deposited onto silicon
                                                                          dioxide with no need
                                                                          for lithographic
http://www.iht.rwth-aachen.de/en/Forschung/nano/bottomup/deposition.php   patterning.
                Making Nanodots
Process for making                  Polymer template for nanodot

   nanodots
1. Apply layer of self-
   assembled polymer
   film.
2. Grow layer of
   desired material to
   create nanodot.

65 billion nanodots per square cm
                                    http://news.bbc.co.uk/1/hi/sci/tech/33010241.stm
                                               Nanodots

   Each nanodot can
    hold one bit of
     information.




                                                                                 13 nm high
      10 Trillion dots                                                           80 nm wide
      per square inch.

                                            Self Assembled Nanodots

http://physics.nist.gov/Divisions/Div841/Gp3/Projects/Atom/atom_dots_proj.html
           Properties of Carbon
               Nanotubes
   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 Nanotubes
                                                               Semimetallic and
                                                                semiconducting



metallic




           http://www.tipmagazine.com/tip/INPHFA/vol-10/iss-
                              1/p24.html
           Growing 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 Transistor
                                                   Basic diagram for a
                                                    nanotube transistor
                                                   Benefits of transistor over
                                                    conventional designs:
                                                    – Smaller
                                                    – Faster
                                                    – Less material used
                                                    – Many of the problems
www.nanotech-now.com/ news.cgi?story_id=06788
                                                       associated with
                                                       conventional devices are
                                                       solved
               Nanotube Transistor-self
                     Assembled
          Amine silane
                                                          Ti/Au Contact

                                                                 AFM Image

                                                                   SiO2


                                                                Carbon Nanotube


                                          Diagram of Nanotube
                                               transistor
www-drecam.cea.fr/.../ LEMautoassemblage.html
          Nanotube Transistor
          Construction 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/2004/12150
                                 4/DNA%20makes%20nanotube%20transist
                                             ors%20Image.html
                  Problem With Carbon
                  Nanotube 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
                 (SAMS)
                                                        Molecules are
                                                         deposited molecule-
                                                         by-molecule to form a
                                                         self-assembled
                                                         monolayer.
                                                        Creates a high quality
                                                         layer of material.
                 http://www.mtl.kyoto-                  Layers are deposited
u.ac.jp/english/laboratory/nanoscopic/nanoscopic.htm
                                                         one layer at a time.
                                Monolayers
                                              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
http://www.orfid.com/images/img-vofet1.gif
                                               semiconductors.
                               Carbon Nanowire
                                Interconnects
                                                                   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 Process




   http://www.nasa.gov/centers/ames/research/technology-onepagers/carbon_nanotubes_vertical.html
         Benefits and Challenges of
          Nanotube Interconnects
Carbon nanotubes                                           Can have a much greater
grown on a metal              Carbon nanotubes after
                              layer of silicon dioxide      conductivity than copper.
 contact through
    PECVD.                             added.              Is more heat resistant than
                                                            copper.
                                                           Carries a much larger
                                                            current than copper.
                                                           Orientation of carbon
                                                            nanotubes remains a
  http://www.nasa.gov/centers/ames/research/technology-     problem.
         onepagers/carbon_nanotubes_vertical.html
                                                           Technology is not reliable
                                                            enough to be used in
                                                            device manufacturing.
Challenges for the Bottom-Up
         Approach
 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
                       Processing
                                                                  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&c
          ontent_type=application/pdf&filename=Paper%2036.pdf
            Future of Top-down and
             Bottom-Up Processing




http://www.imec.be/wwwinter/business/nanotechnology.pdf
    Advancements 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 For
                                     Nanotube array possibly used in
   Vias and interconnects being
                                           future televisions.
    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/
               Conclusion
 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.

								
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