Nova 600 NanoLab Dual beam Focused Ion Beam IITKanpur

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1 Nova 600 NanoLab Dual beam Focused Ion Beam IITKanpur Dual Beam Nova 600 Nano Lab From FEI company (Dual Beam = SEM + FIB) SEM: The Electron Beam for SEM Field Emission Electron Gun Energy : 500 ev to 30 kev Current : 0.7 pa to 37 na Beam spot size : 1.1 to 10 nm Magnification upto X FIB : The Ga Ion Beam for FIB modifications Ga liquid metal ion source (LMIS) Energy : 5 kev to 30 kev Current : 0.3 pa to 20 na Beam spot size : 7 to 15 nm Five Gas injector systems : For fabrication of nano structures. C deposition [Naphthalene: C10H6] Pt deposition [Methyl Cyclopentadienyl trimethyl Platinum: (CH3)3Pt(CpCH3)] W deposition [Tungsten Hexacarbonyl: W(CO)6] Insulator enhanced etch [Xenon Fluoride: XeF2] Enhanced etch [Iodine: I2] Residual gas analyzer (SRS RGA-300) : For analyzing the gases released during fabrication. Fast electron beam blanker (For electron beam lithography) Everhart-Thornley secondary electron detector Ultra thin Window sapphire detector (For EDS analysis) Usage and Applications: The Electron Beam is mainly utilized for insitu SEM imaging. The electron Beam can also be used for milling. The Electron Beam can also be utilized for electron beam lithography (EBL). In the Focused Ion Beam (FIB) system Ga+ ions are created, focused and accelerated toward a surface with large electric fields. The Ga+ ion beam can then be used to image or to nano-machine a surface. With the FIB we can build complex structures at the nanoscale. Most modern FIBs are combined with SEMs for easier operation and synergistic analysis. Ga+ is the most common LMIS used for commercial FIBs because it offers the best of all properties needed. Contacting of small structures by metal deposition. Non perpendicular sections. EDX line scan of mapping on a section. EBSD mapping on a section. Automated repeated cross sectioning 3D image TEM Lamella preparation. Deposition /milling with feature mill. Industrial Process Solution.

2 Carbon Cantilever for femto gram weight measurements A die in Silicon for fabrication of micron/nano size gear of polymers 50nm holes in NbSe2 for magnetic vortex characteristics Fabrication of Micro Squid with Nb thin Films Nano Electrodes

3 FIB System Components: A Vacuum system and chamber A liquid metal ion source An Ion column for milling and deposition Ion column consists of : Ga+ source (LMIS) ion optics (electrostatic lenses) fast beam blanker (electrostatic) different currents (aperture stripe) adjustable acceleration voltage An Electron column for imaging (SEM) A precision goniometer for sample mounting and manipulation Imaging detectors A gas injection system to spray a precursor gas on the sample surface Scan generators for ions and electrons Computer control.

4 Liquid Metal Ion Source(LMIS) LMIS Consists of a capillary tube with a needle through it an extraction electrode and a shielding. Capillary acts as a reservoir that feeds the metal to the tip. Heated Ga flows and wets the W needle having tip radius 2-5 µm. A suppresser voltage [electric field (10 8 V/cm)] applied to the end of the wetted tip causes the liquid Ga to form a point source (2-5 nm tip) in the shape of Taylor cone. Conical shapes forms because of electrostatic and surface tension force balance. An extraction voltage pulls Ga from the tip and efficiently ionize it by field evaporation of the metal at the end of the Taylor cone. Why Ga LMIS? 1. Low melting point (Tmp= C) minimizes any reaction of interdiffusion between the liquid and the W needle substrate. 2. Low volatility at the melting point conserves the supply of metal and yields a long source life. 3. Low surface energy promotes viscous behavior on the (usually W) substrate. 4. Low vapor pressure allows Ga to be used in its pure form instead of in the form of an alloy source and yields a long lifetime since the liquid will not evaporate. 5. Excellent mechanical, electrical, and vacuum properties. 6. Emission characteristics enable high angular intensity with a small energy spread. SEM imaging FIB imaging:(low ion current) Impinging Ga+ produce secondary electrons ET or in Lens detector Typically at 30 kv, 40 pa optimal resolution and signal Other currents and energies different contrast Advantages: Channeling contrast Removal of oxide layer Disadvantages: Damage of surface Remark : Now a days there is scanning He microscopy having high contrast and very high resolution

5 Focused Ion Beam (FIB): interaction with sample Ga+ beam hits the sample substrate and yields 1. Secondary electrons 2. Sputtered atoms and ions 3. Implantation of Ga 4. Amorphisation/recrystallization 5. Imaging, milling and deposition happen simultaneously Remarks: 1. Implantation and amorphisation also occur at grazing incidence. 2. Depth of damage layer depends also on energy of Ga+. Focused Ion Beam (FIB): Nano Scale milling (High ion current) For milling applications it is desirable that the incoming ions interact only with the atoms at the surface. If the ion energy (momentum) is adequate the collision can transfer sufficient energy to the surface atom to overcome its surface binding energy ( 3.8eV for Au and 4.7 ev for Si). Interaction solely depends on momentum transfer to remove the atoms, sputtering is purely a physical process. Note: There are other variants of the process like Reactive Ion Etching (RIE) where chemical species are incorporated and the process proceeds chemically Focused Ion Beam (FIB): deposition (Gas assisted) Focused ion beam scanning is our hand which defines the deposition area. Three dimensional nanostructures can be fabricated using layer by layer deposition. For FIB induced deposition, the necessary processes are Adsorption of the chemical precursor onto the sample surface. Decomposition of gas molecules into volatile and non volatile products by focused ion beam. Precursor must have two properties, namely : Sufficient sticking probability to stick to a surface of interest in sufficient quantity. Decompose more rapidly than it is sputtered away by the ion beam. Examples of species that can be deposited: C, Pt, W, Pd, SiO2