Please click here for a copy of this presentation.
Refer to the original PDF for tables, figures and page layout.
Page 1\n1\nMechanical TEM Sample Preparation\nPablo Mendoza\nJessica Enos\nAllied High Tech Products, Inc.\n\n\nPage 2\n2\nOverview\n• Basics\n– What is a TEM sample?\n– What are the requirements?\n– What are the methods of \npreparing TEM samples?\n• Thin Film Preparation \nProcess\n\n\nPage 3\n3\nWhat is a TEM Sample?\n• TEM\n– Transmission Electron \nMicroscopy is a microscopy \ntechnique in which a beam of \nelectrons is transmitted though a \nspecimen to form an image.\n• TEM Sample\n– A specimen that is usually ultra \nthin (<100 nm) so that electrons \ncan be transmitted through it.\nZeiss HRTEM [3]\n\n\nPage 4\n4\nTEM Sample Requirements\n• Must be electron transparent\n• Must have a submicron \nthickness\n• Must have an area of ≤3 mm to \nfit various TEM grids and \nholders\n• Any deformation from previous \nprocessing must be removed.\nTwo-specimen holder with double-tilt [3]\nSpecimen support grids of \ndifferent mesh sizes and shapes [3]\n\n\nPage 5\n5\nCommon Methods of Preparation\n• Ion Milling/FIB\n• Electropolishing\n• Mechanical Preparation\n–Thin Film Preparation\n\n\nPage 6\n6\nIon Milling/FIB\n• Bombarding a TEM sample with energetic \nions or neutral atoms and sputtering \nmaterial from the sample until it is thin \nenough to study in the TEM [3]\n• A versatile thinning process that can be \nused for a wide variety of materials\n• Is expensive to purchase and run\n• Implantation of source material and an \namorphous layer is created\nSchematic of a two-beam FIB and stages \nin making TEM samples using a FIB [3]\n\n\nPage 7\n7\nElectropolishing\n• Immersing a sample in an electrolyte and \nsubjecting it to a direct electrical current\n– Keep the sample anodic with a cathodic \nconnection to a nearby metal conductor [2]. \n– The anodic dissolution of the sample polishes \nthe surface.\n• Relatively quick and can produce samples \nwith no mechanical damage\n• Can only be used for electrically conductive \nmetals and alloys\nThe Window Method [3]\n\n\nPage 8\n8\n• Smoothing the sample surface using abrasives \nand mechanical tools\n• Common types:\n– Manual: Uses hand tools (tripods) that allow \nthe user to make angle adjustments\n– Semi-Automatic: Uses precision polishers \nwith digital indicators and micrometers\n– Dimpling: Mechanical dimplers use a \nsmall-radius tool to grind and polish samples \nto a fixed radius of curvature in the center.\nMechanical Preparation\n\n\nPage 9\n9\n• Advantages\n– TEM Wedge Capabilities\n– All damage removed using proper \nmaterial removal procedures\n– No foreign material implanted\n– Repeatable and fast with \nexperience\n– Lower cost of required equipment\n– Decreases milling time and costs\n• Disadvantages\n– Requires careful handling \nthroughout the process\n– Greater learning curve than other \ntechniques\n– Some samples may require \nadditional processing using one \nof the other TEM preparation \ntechniques\nMechanical Preparation\n\n\nPage 10\n10\nThin Film Preparation Process\n– Preparing the Sample\n– Fixturing\n– Grinding the Pyrex®\n– Thinning the First Side\n• Thin film samples are commonly prepared using \nmechanical methods. The process includes:\n– Flipping the Sample\n– Stopping Point\n– Inducing a Wedge\n– Color and Fringes\n\n\nPage 11\n11\n• Wafers are scribed down to a \nmanageable size.\n• Using an appropriate adhesive, \nsuch as M-Bond 610, the thin film \nsurfaces are “sandwiched” \ntogether.\nPreparing the Sample\n\n\nPage 12\n12\n• The surface of the Pyrex® piece on a \nthinning fixture requires grinding to ensure \nit is parallel to the platen, or the grinding \nplane.\n• Pyrex® can be ground using diamond \nlapping films.\n– A 15-9 µm finish is acceptable.\n– Do not polish the surface; having some \nscratches will help with adhesion.\nGrinding the Pyrex®\n\n\nPage 13\n13\n• Secure the sample on a thinning fixture with \nmounting wax.\n• Place the fixture on a hot plate to melt the wax.\n• Apply light pressure using a cotton-tipped \napplicator to assist in parallel registration of \nthe sample to the fixture.\nFixturing\n\n\nPage 14\n14\n• Abrasive: Diamond Lapping Films\n– Provide excellent edge retention \nand maintain coplanarity\n– Typically used for \nunencapsulated cross-sectioning, \nTEM preparation, backside \npolishing, etc.\nThinning the First Side\n\n\nPage 15\n15\n• The sample surface is \ndamaged throughout the \ngrinding process.\n– Scratch patterns\n– Micro-cracks that can \npropagate further into the \nsample\nSample\nDamage\n(micro-cracks)\n30 µm DLF\n15 µm DLF\nAOI\n9 µm DLF\n30 µm \nDLF\nThinning the First Side\n\n\nPage 16\n16\n• Remove 3 times the \nprevious abrasive to \ncompletely remove any \ndamage.\n– Ex: If a 30 µm lapping film \nis followed by a 15 µm \nlapping film, the 15 µm film \nmust remove at least \n90 µm (3 x 30 µm) to \ncompletely remove any \ndamage.\nCurrent Step\n(DLF)\nCurrent \nDistance from \nTarget\nPrevious Step\nRemove At \nLeast 3x \nPrev. Step \nSize\nDistance to \nTarget After \nCurrent Step\n30 µm\nVaries\nN/A\nN/A\n192 µm\n15 µm\n192 µm\n30 µm\n90 µm\n102 µm\n9 µm\n102 µm\n15 µm\n45 µm\n57 µm\n6 µm\n57 µm\n9 µm\n27 µm\n30 µm\n3 µm\n30 µm\n6 µm\n18 µm\n12 µm\n1 µm\n12 µm\n3 µm\n9 µm\n3µm\n0.5 µm\n3 µm\n1 µm\n3 µm\nAt Target\n3X Rule\n\n\nPage 17\n17\n• Certain materials, such as ductile steels, may only require a \n“2X Rule.”\n• Fragile, brittle materials, such as ceramics, may require a \n“4X Rule” since cracks can propagate further into the \nsample.\n• Main Concept: No matter what steps follow, all damage \nintroduced by the previous abrasive must be removed to \nobtain an accurate representation of the microstructure.\n3X Rule\n\n\nPage 18\n18\n• Reheat the fixture on a hot plate.\n• Carefully remove and clean the \nsample, and then place it back on \nthe fixture with the polished side \nface down.\n• Thin the sample according to the 3X \nrule.\nFlipping the Sample\n\n\nPage 19\n19\nPre-FIB Thinning\n• Remove the sample to prepare \nfor FIB thinning by placing the \npaddle into a piece of filter \npaper, and then into a container \nof acetone to remove the wax.\nThinned to \nelectron \ntransparency\nThick enough \nfor handling\nTEM Wedge\n• Induce an angle to create a \nwedge sample.\n• The degree of the angle \ndepends on the material being \nprepared.\nGoal: Pre-FIB or TEM Wedge?\n\n\nPage 20\n20\n0.02°\n• Micrometers on precision \npolishers are used to induce an \nangle on the sample and create \na wedge.\nParallel contact plane \nInducing a Wedge\nThinned to \nelectron \ntransparency\nThick enough \nfor handling\n\n\nPage 21\n21\n• Bulk\n– Homogeneous material\n– Can stop anywhere; only a useable \narea is needed\n• Thin Film\n– Film on material deposited on \nsurface\n– Prepared properly, can stop \nanywhere\nAreas of \nInterest\nWhen is the Sample Complete?\n\n\nPage 22\n22\n• Certain TEM samples can display a series \nof colors in regions <10 µm thick with a \ntransmitted light microscope.\n• Fringes can also occur in regions <2 µm \nthick.\n• Colors that correspond with different \nthicknesses vary based on materials; \nhowever, some are well documented, \nsuch as silicon.\nColor and Fringes\n\n\nPage 23\n23\n• Color and fringe information \ncan be used to assist in the \npreparation of TEM samples, \nas they are a guide to overall \nprogress during a TEM wedge \nprocedure.\nCorrespondence between Si wafer thickness and color of transmitted light [4]\nColor and Fringes\n\n\nPage 24\n24\n\n\nPage 25\n25\n\n\nPage 26\n26\nReferences\n•\n1. Allied High Tech Products, Inc., http://www.alliedhightech.com/. Accessed \n16 September 2019.\n•\n2. Delstar Metal Finishing, Inc., Electropolishing A User’s Guide to \nApplications, Quality Standards and Specifications, \nhttps://www.delstar.com/assets/pdf/epusersguide.pdf. Accessed 23 May 2018.\n•\n3. Williams, David B, and C B. Carter. Transmission Electron Microscopy: A \nTextbook for Materials Science. New York: Plenum Press, 1996. Print.\n•\n4. Yougui Liao. Practical Electron Microscopy and Database. URL: \nhttp://www.globalsino.com/EM/page2805.html. GlobalSino 2007.\n\n\nPage 27\n27\nQuestions\nPablo Mendoza\nLaboratory Supervisor, \nTechnical Services\nAllied High Tech Products, Inc.\npmendoza@alliedhightech.com\nJessica Enos\nSr Materials Engineer, \nTechnical Services\nAllied High Tech Products, Inc.\njmenos@alliedhightech.com\nTechnical Services\nAllied High Tech Products, Inc.\n(800) 675-1118 (North America)\n(310) 635-2466 (Worldwide)\nlab@alliedhightech.com\n