Email: dashp@nitrkl.ac.in Office: BM-406, Mob: 8895121141 Webpage: http://homepage.usask.ca/~prd822/ MB: 205
Nonmanufacturing In continuation from last class... 2
Top-Down methods Mechanical-energy methods Thermal fabrication methods High-energy and particle methods Lithographic methods Chemical methods Natural processes 3
Thermal methods Annealing Chill-block melt spinning Electrohydrodynamic atomization (EHDA) Electrospinning Liquid dynamic compaction (LDC) Gas atomization Evaporation Template extrusion Sublimation Thermolysis / Pyrolysis Combustion Polymer carbonization 4
Electrospinning High voltage is applied to a polymer melt solution to induce charging. Thin layers of filaments from a bulk polymer solution are able to generate fibers of nanoscale diameter. 5
Gas Atomization The idea is to transfer the kinetic energy from a supersonic jet of gas to a stream of liquid metal causing it to break up into droplets. 6
High-Energy methods Arc discharge Laser ablation Solar energy vaporization Plasma methods Ion milling Electron-beam evaporation Reactive ion etching (RIE) Pyrolysis Combustion High energy sonication 7
Arc -discharge methods Two carbon rods placed facing each other with about 1 mm gap, in an enclosure that is filled with either helium or argon gas. The arcvaporization of carbon creates nanotubes. The carbon arc discharge method is the most common and perhaps easiest way to produce CNTs. It is a technique that produces a complex mixture of components, and requires purification -to separate the CNTs from the soot and the residual catalytic metals present in the crude product. 8
Top-down Lithography Photolithography Immersion lithography Deep ultraviolet lithography (DUV) X-ray lithography (XRL) Electron-beam lithography Focused ion beam lithography (FIBL) Microcontact printing methods Nano imprint lithography (NIL) Nanosphere lithography (NSL) Scanning AFM nano-stencil Scanning probe nano-lithographies 9
Lithographic Processing The word lithography comes from the Greek lithos, meaning stones, and graphia, meaning to write. It means quite literally writing on stones. In the case of semiconductor lithography (also called photolithography) our stones are silicon wafers and our patterns are written with a light sensitive polymer called a photoresist. To build the complex structures that make up a transistor and the many wires that connect the millions of transistors of a circuit, lithography and etch pattern transfer steps are repeated at least 10 times, but more typically are done 20 to 30 times to make one circuit. Each pattern being printed on the wafer is aligned to the previously formed patterns and slowly the conductors, insulators, and selectively doped regions are built up to form the final device. 10
Lithographic Processing Coat, protect, expose, etch, repeat Result: Multiple patterned layers of different materials. 11
Lithographic Processing The resist material is applied as a thin coating, typically by spin coating over the substrate (wafer) and then heated to remove the casting solvent (post-apply bake, pre-exposure bake, or pre-bake). The resist film is subsequently exposed in an image-wise fashion through a mask (in photoand X-ray lithography) or directly with finely focused electron beams. The exposed resist film is then developed typically by immersion in a developer solvent to generate three-dimensional relief images. The exposure may render the resist film more soluble in the developer, thereby producing a positive-tone image of the mask. Conversely, it may become less soluble upon exposure, resulting in generation of a negative-tone image. When the resist image is transferred into the substrate by etching and related processes, the resist film that remains after the development functions as a protective mask. The resist film must "resist" the etchant and protect the underlying substrate while the bared areas are being etched. The remaining resist film is finally stripped, leaving an image of the desired circuit in the substrate. The process is repeated many times to fabricate complex semiconductor devices. 12
Lithographic Processing 13
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Dip-Pen Lithography Dip pen nanolithography can be used in a range of applications from semiconductor patterning and chip manufacturing to biomedical and pharmaceuticals development. Dip-Pen Nanolithography (DPN) is a direct write lithographic technique that uses an atomic force microscope (AFM) to build a pattern on the substrate material rather than etching it away. In the same way that an old fashioned dip pen picks up ink from an ink well and is then used to write on paper, molecules are picked up from a reservoir on the end of the AFM tip and deposited to the surface of the substrate via a solvent or water. 15
Dip-Pen Lithography 16
Lithographic Processing: Masking and Exposure 17
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