Nano fabrication Technology by kunalup


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									                 NANO FABRICATION

ABSTRACT:                                   meter, or 10-9m. One nanometer is

               Current    scenario   the    approximately equivalent to 10 hydrogen

world   is    focusing   on   Nanoscale     or 5 silicon atoms aligned in a line.

components.      To      achieve     this                                  By           this

nanofabrication techniques are evolved.     technology the structures of the devices

In this paper an attempt is made to         at atomic, molecular and supramolecular

discuss various processes available for     levels     and   can    be     controlled    to

nanoscale fabrication. The principle and    manufacture and use these devices. All

operation of each process was discussed.    the relevant phenomenon at nanoscale
                                            are caused by tiny size of the organized
                                            structure as compared to molecular
                                            scales and by the interactions at their
                                            predominant and complex surfaces. The

INTRODUCTION:                               need      to   study   nanotechnology        is,
                                            materials in micrometer scale mostly

NANOTECHNOLOGY:                             exhibit physical properties the same as
                                            that of macro scale, however, materials

Nanotechnology can be defined as            the      nanometer     scale   may    exhibit

structural features ranging from 1 to 100   physical properties distinctively different

nanometers which determine important        from that of bulk. Materials in this size

changes as compared to the behavior of      range exhibit some remarkable specific

isolated molecules or of bulk materials.    properties.

A nanometer (nm) is one billionth of a
REASONS FOR MAXIMUM OF 100                           development of Bio-inspired materials,
NANOMETERS:                                          development of cost effective and
                                                     scalable production technologies and
  1) It is not clear how to economically             determination          of         the      nanoscale
      fabricate        nano           structured     initiations of future.
      electronics.                .
  2) Even if fabricated, the physical or             APPLICATIONS:
      chemical       properties       of    those     1) Net-shaped              manufacturing            of
      nanostructures are unknown; the                       nanostructure metals and ceramics.
      present electronic devices are all              2) Improved printing brought about by
      based on models critical scale                        nanometer scale particle that have
      lengths in the 100nm range.                           the best properties of both dyes and
  3) Without known properties it is                         pigment.
      impossible to design a functional               3) Nanoscale cemented and planted
      device, fabricated and assemble                       carbides   and        Nanocoatings           for
      the devices into a working system.                    cutting tools, electronic chemical
                                                            and structural applications.
MATERIAL                                    AND       4) Nanofabrication on a chip with high
MANUFACTURING:                                              levels     of         complexity            and
                                            By              functionality.
using this technology the materials
having properties like lighter, stronger
and programmable, reduction in life                  NANOMANUFACTURING:
cycle costs through lower failure rates,
innovative   devices      based        on    new     Manufacturing          can        be     defined     as
principles and architectures and use of              transforming raw materials into products
molecular/cluster manufacturing.                     with       desired           properties            and
CHALLENGES WILL INCLUDE:                             Nanomanufacturing aims at material
                                                     structures,                             components,
Synthesis    of   materials       by       design,   devices/machines            and        systems     with
nanoscale   features   in   1,   2   or 3     production of electronic components.
dimensions by making use of                   Current scenario research has been
   1) Bottom-up (synthetic) directed          concentrated at nanoscale fabrication
      self-assembly of nanostructure          with the application of new technologies
      building blocks, from atomic,           like
      molecular and supramolecular            .
      levels.                                     1) Lithography
   2) Top-down (transformative) high-             2) Etching
      resolution,      ultra     precision        3) wet etching
      engineering           fragmentation         4) plasma technique
      methods positioning assembly.               5) Mask fabrication
   3) Engineering of molecules of                 6) Unconventional         machining
      molecules and supramolecular                   processes.
      systems, molecular as devices
      ‘by design’, nanoscale machines.
   4) Hierarchical     integration    with    LITHOGRAPHY:
      larger scale systems.                                       Lithography        is
CHALLENGE                              IN     defined as ‘to fix the reflection of the
NANOMANUFACTURING:                            mirror and make a picture without the
   1) Need selective impurity removal.        aid of the artist’s pencil’. Lithographic
   2) Need to under stand the adhesion        patterns are formed by the exposure of a
      of        surface,         particles,   resist material to a type of radiation.
      nanoelements in a variety of            Sub-100nm features have been patterned
      conditions and situations.              with electrons, ions, and X-rays. The
   3) Cleaning nanostructures without         first two methods involve the serial
      destroying them.                        writing of a pattern with a small focused
   4) Reproducibility.                        probe. The small probe is formed
                                              through an electrostatic/magnetic lens
NANOFABRICATION:                              system or by proximity to an STM tip. In
                       Fabrication       at   X-ray lithography, an entire mask
nanoscale has great importance in the         pattern is printed at one time by a flood
exposure of X-rays through a mask or                               The        substrate
reflected from a mask.                        (wafer) is chemically cleaned to remove
                                              particulate matter as well as any traces
                                              of organic, ionic, and metallic impurities
                                              on the surface. The thin film of some
                                              selective material for example, silicon
                                              dioxide is placed on substrate It is
                                              required that some of the silicon dioxide
                                              is to be selectively removed so that it
                                              only remains in particular areas on the
                                              substrate. For this we need to produce a
                                              mask is typically a glass plate that is
                                              transparent to ultra violet (U.V) light.
                                              The pattern of interest is generated on
                                              the glass by depositing a very thin layer
                                              of metal, usually chromium or gold.
                                              These masks are capable of producing
                                              very high quality images of micron and
                                              even sub-micron features.
                                              The next phase of this process is the
                          Electron-beam       coating of the photo resistive material on
lithography has been the most widely          the coating on the wafer. This material
used       method        of     fabricating   should be sensitive to U.V light. Organic
nanostructures. It is also called as          polymers are usually chosen. Once the
photolithography. Photolithography is         photo resist coating is completed, the
the processes of using light to create a      photo mask is placed over it. The U.V
pattern i.e.; mask and subsequently           light is allowed to fall on the mask. U.V
transfer    it   onto     the    substrate.   light is known as ‘exposing energy’.
Photolithography is an optical means of       Depending upon the thickness photo
transferring patterns.                        resist materials, the exposing process
                                              may be performed once or several times
i.e.; multi exposure fabrication. U.V rays    A substrate is a sheet of base material in
dosage should be accurate and some            which      mechanical         parts,   electronic
times additional exposure cause large         components and integrated circuits (I.C)
internal stress in the resist layer leading   are built by the process of etching. The
to poor adhesion between the resist layer     etching process is used to remove a
and the substrate. The internal stresses      defined portion of the substrate in a
may lift-off the structure from the           particular manner so that the desired
substrate during subsequent processes.        shape can be obtained. The material to
Light may fall on the entire area of the      be removed is determined by the etching
photo resist in one go or in sequence by      solution (called etchant). Some typical
employing     a    scanning     technique.    structures such as plates, steps, grooves,
Scanning is achieved by moving a small        cantilever, diaphragm, post, etc can be
spot of light over the desired area of        fabricated or micro machined through
photo resist. When U.V light falls on the     etching.
photo resist pattern is developed on the      In   Isotropic        etching,    materials    are
photo resist layer. This phenomenon is        removed uniformly from all directions
called mask transformation or pattern         and it is independent of the plane of
transformation. The soluble photo resist      orientation      of     the      crystal   lattice.
becomes weakened when exposed to              Isotropic etching is used for polishing,
U.V light. In practice, the photo resist is   cleaning and unidirectional etching of
washed awa6y in the region where the          the materials. The etchants are a mixture
light   was   struck,   conversely,    the    of acidic solutions such as HF, HNO3
negative photo resist not.                    and CH3COOH. In single crystal silicon
                                              the etchant leads to round isotropic
ETCHING:                                      features. They can be used at room
              One of the important sub-       temperatures or slightly above, but
processes in micromachining is etching,       below 500C.
which means the removal of selective
materials. Etching is performed either on
the substrate (wafer) or on a preferred
material layer deposited on the substrate.
                                                  etching process passes through the
                                                  following steps:
                                                     1) Reactant transportation to the
                                                     2) Surface reaction and
                                                     3) Reaction product transportation
                                                         (away from surface). Etching
                                                         depends strongly on temperature,
                                                         material and composition of the

solutions are primarily used to etch the
silicon     substrate   on   the    plane    of
crystallization. Hence, it is known as wet
etching. Wet etching of silicon is used
mainly for cleaning, shaping, polishing
and       characterizing     structural     and
compositional features. Wet etching can
                                                               The high vapor pressure
provide a higher degree of selectivity
                                                  developed during laser irradiation can be
than dry etching techniques. In many
                                                  used for cleaning of contaminations on
cases wet etching is faster and an etch
                                                  electronic   components.   Because    no
rate up to 6um/min can be achieved. The
                                                  mechanical or chemical treatment is
necessary, laser cleaning is free from     3. Electrochemicalmachinng
possible mechanical damage and is          4. Laser Beam machining
environment friendly. Conventionally,      5. Plasma arc machining
laser beam is fixed directly on the        6. Electric discharge machining
surface to be cleaned but in this case
thermal damage of the sample may           ION BEAM MACHINING:
occur. Recent technique adopts a method                         In this process the
to focus the laser beam in air above the   beam ions is impinged on the work
surface and generate plasma in which       piece. The ion when strikes surface of
cleaning is done by the high pressure of   the work piece ion will bombard with
the expanding plasma.                      the atoms and causes the removal of that
                                           atom. If this process can be controlled to
                                           attain   the   removal     of   nanoscale
                                           dimensions is nothing but Nanoscale

                                           ELECTRON BEAM MACHINING:
                                                                    The      electron
                                           beam strikes the work piece, electron
                                           will, liberate the atom on the surface by
                                           the excitation of outer most orbit
                                           electron. The process can be controlled

UNCONVENTIONAL MACHINING                   to achieve nanoscale material removal.

                             In spite of   ELECTROCHEMICAL

these techniques Nanoscale fabrication     MACHINING:

can be achieved by the processes like
1. Ion Beam machining                      Electrochemical machining is based on

2. Electron Beam machining                 the principle of electrolysis. In a metal,
electricity is achieved through the               3) Melting, vaporization.
movement of ions. Thus, the flow of
current through an electrolyte is always      PLASMA ARC MACHINING:
accompanied by the movement of                                                Plasma is
matter. In electrochemical machining the      a high temperature ionized gas. The
objective is to remove metal, the work        plasma arc machining is done with a
piece is connected to the positive, and       high speed jet of a high speed jet of high
the tool to the negative, terminal. The       temperature plasma. The plasma jet
gap between the tool and the dissolution      heats up the work piece, causing a quick
of the anode occurs. However, the             melting. Plasma arc machining can be
dissolution rate is more where the gap is     used on all materials which conduct
less and vise versa as the current density    electricity, including those which are
is inversely proportional to the gap.         resistant to oxy-fuel gascutting.This
Now, if the tool is given a downward          process are extensively used for profile
motion, the work surface tends to take        cutting of stainless steel, and super alloy
the same shape as that of the tool, and at    plates.
steady state, the gap is uniform. The
shape of the tool is reproduced in the        ELECTRIC                   DISCHARGE
job.                                          MACHINING:
                                                                               In    this
LASER BEAM MACHINING:                         process the main principle involved is
                                In     this   when beam of electrons strikes the work
process principle involved is the increase    piece the kinetic energy of electrons is
in temperature of the work material up to     converted into heat energy which will
the     melting      point;   vaporization.   cause the material to melt and evaporate.
Machining by laser beam is achieved           To achieve this work and tool are made
through the following phases:                 electrodes current will flow across them
      1) Interaction of laser beam with       as the electrolyte pass in between.
         work material,
      2) Heat conduction and temperature      CONCLUTION:
         rise, and
                   Although many of the
fundamentals have long been established
in different fields such as in physics,
chemistry, material science and device
science and technology, and research on
nanofabrication     is     based   on      these
established        fundamentals              and
technologies, researchers in the field
face many new challenges that are
unique        to    nanostructures           and
nanomaterials.            Challenges           in
nanofabrication include the integration
of nanostructures and nanomaterials into
or with macroscopic systems that can
interface with people.


   1) Nanostructures                         and
         nanomaterials                         --
         -------Imperial college press.
   2) Micro              fabrication         and
         nanotechnology                     -----
         --- N.P.Mahalik (Ed)
   3) The material science of thin films
         -------- M .Orhing
   4) Nanotechnology
         --------- H.Goronkin
   5) Northern                         California
         nanotechnology center (NC2) ----

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