Current scenario the world is focusing on Nanoscale components. To achieve this nanofabrication techniques are evolved. In this paper an attempt is made to discuss various processes available for nanoscale fabrication. The principle and operation of each process was discussed.
Nanotechnology can be defined as structural features ranging from 1 to 100 nanometers which determine important changes as compared to the behavior of isolated molecules or of bulk materials. A nanometer (nm) is one billionth of a meter, or 10-9m. One nanometer is approximately equivalent to 10 hydrogen or 5 silicon atoms aligned in a line.
By this technology the structures of the devices at atomic, molecular and supramolecular levels and can be controlled to manufacture and use these devices.
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 performances. 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 surface, 2) Surface reaction and 3) Reaction product transportation (away from surface). Etching depends strongly on temperature, material and composition of the solution. WET ETCHING PROCESS: Chemical 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 PLASMA: 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 fabrication. 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. PROCESSES: 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. REFERENCES: 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) ---- ------California.
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