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Lithography (and briefly, Electrodeposition) ibm bnl UMass manchester July 10, 2008: Nano Education Institute at UMass Amherst How do we control the shape and size of nanostructures? Self Assembly (inspired by nature) Lithography (designed by humans) Nanostructures macroscale (3D) object nanofilm, or nanolayer (2D) height depth width nanowire, nanorod, or nanocylinder (1D) nanoparticle, nanodot, quantum dot (0D) Computer Microprocessor "Heart of the computer" Does the "thinking" Making Small Smaller An Example: Electronics-Microprocessors microscale nanoscale macroscale ibm.com Nanofilms (making thin objects, controlling the thickness) An example of a FILM A monolayer NANOFILM (single layer of molecules) ~1 nm thick Langmuir film This is an example of SELF-ASSEMBLY Nanofilm by Electrodeposition ("electroplating") I V cathode Working Electrode (WE) CuSO4 dissolved in water anode Counter Electrode (CE) If using an inert Pt electrode: 2 H2O –> O2 + 4H+ + 4e- "reduction" Cu2+ + 2e- –> Cu(0) "oxidation" Cu(0) –> Cu2+ + 2e- A nanofilm method, Thermal Evaporation Vaporization or sublimation of a heated material onto a substrate in a vacuum chamber sample QCM film vapor Au, Cr, Al, Ag, Cu, SiO, others Pressure must be held low to prevent contamination! There are many other thin film manufacturing techniques vacuum ~10-7 torr source resistive, e-beam, rf or laser heat source vacuum pump Nanofilms (making thin objects) From DOE A Few Nanostructures Made at UMass 100 nm dots 18 nm pores 70 nm nanowires 12 nm pores 14 nm nanowires 13 nm rings 200 nm rings 14 nm dots 25 nm honeycomb 150 nm holes Lithography (controlling width and depth, by using stencils, masks, & templates) Lithography Nanoscience Rocks! Rocks (Using a stencil or mask) Lithography: Basic concepts Some possible desired features narrow line narrow trench modified substrate •Photolithography •Electron-Beam Lithography •X-ray Lithography •Focused Ion-Beam Lithography •Block Copolymer Lithography •Nano Imprint Lithography •Dip Pen Lithography •Interference Lithography •Contact Lithography •Others Photolithography Photolithography for Deposition process recipe spin coating substrate apply spin bake spin on resist resist expose mask (reticle) exposed unexposed "scission" develop deposit liftoff narrow line Lithography IBM Copper Wiring On a Computer Chip Patterned Several Times Patterned Oxide Other Uses Ion implantation substrate silicon oxide silicon spin on resist resist dopant ions (e.g., B+, P+) Etching expose mask after develop etch lift off lift off narrow trench Positive and Negative Resists Positive Resist Negative Resist resist resist expose expose scission cross-linking develop develop deposit & liftoff deposit & liftoff exposed region results in presence of structure exposed region results in absence of structure (generally poorer resolution) Several Types of Lithography lens contact high resolution proximity extends mask life projection enables "stepping" Resolution Limit of PL How low can you go? minimum linewidth minimum pitch There are actually many contributing factors that limit the minimum linewidth: • optical diffraction () • resist sensitivity • depth of focus • purity of light source • numerical aperture of lens Resolution in Projection Lithography k1 R NA k1 ~ 0.4 - 1.1 (depends on materials, optics and conditions) is wavelength of light used NA ~ 0.16 - 0.6 is the numerical aperture of the lens system Rayleigh diffraction criterion—> 2bmin = 0.61/NA is part of the underlying reason With careful engineering, R ~/2 can be achieved Contact Lithography 3 z R 2 2 z is resist thickness Down to 45 nm Electron-Beam Lithography Electron-Beam Lithography Electron Beam Polymer film Silicon crystal Nanoscopic Mask ! Down to 10 nm CORE CONCEPT FOR NANOFABRICATION Deposition Template (physical or electrochemical) Etching Mask Remove polymer block within cylinders (expose and develop) Nanoporous Membrane Down to 3 nm Solar Cells Benefit: Sun is an unlimited source of electronic energy. Konarka Electric Solar Cells Made from single-crystal silicon wafers (conventionally) Sunlight wires - cross-sectional view n-type silicon Voltage p-type silicon + - Current “load” + The load can be a lamp, an electric motor, a CD player, a toaster, etc Nanostructured Solar Cells Sunlight Voltage More interface area - More power! Current “load” + Next.... ....Electrodeposition