ASTM_E_2530_-_06.pdf

Designation:E 2530 06Standard Practice forCalibrating the Z-Magnification of an Atomic Force Microscopeat Subnanometer Displacement Levels Using Si(111)MonatomicSteps1This standard is issued under the fixed designation E 2530;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This practice covers a measurement procedure to cali-brate the z-scale of an atomic force microscope using Si(111)monatomic step height specimens.1.2 ApplicationsThis procedure is applicable either inambient or vacuum condition when the atomic force micro-scope(AFM)isoperatedatitshighestlevelsofz-magnification,that is,in the nanometer and sub-nanometerranges of z-displacement.These ranges of measurement arerequired when the AFM is used to measure the surfaces ofsemiconductors,optical surfaces,and other high technologycomponents.1.3 The values stated in SI units are to be regarded as thestandard.The values given in parentheses are for informationonly.1.4 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1ISO Standards:2ISO Draft International Standard 25178-2 GeometricalProducts Specification(GPS)-Surface Texture:Areal-Part 2:Terms,Definitions and Surface Texture Parameters.ISO Committee Draft 25178-6 Geometrical Products Speci-fication(GPS)-Surface Texture:areal-Part 6:Classifi-cation of methods for measuring surface texture.ISO/TS 21748:2004 Guidance for the Use of Repeatability,Reproducibility and Trueness Estimates in MeasurementUncertainty EstimationGUM:1993 Guide to the Expression of Uncertainty inMeasurement3.Terminology3.13.1.1 Atomic force microscope(AFM),nsurface topogra-phy measurement method whereby the surface height is sensedfrom the mechanical force of attraction or repulsion between aprobe tip and a surface.3.1.2 Coordinate axes,ncoordinate system in which sur-face topographic measurements are performed.3.1.2.1 DiscussionIt is usual to use a rectangular coordi-nate system in which the axes form a right Cartesian set,thex-axis being the direction of tracing colinear with the meanline,the y-axis also nominally lying on the real surface,and thez-axis being in an outward direction(from the material to thesurrounding medium).3.1.3 Si(111),nsingle crystal surface of silicon,orientednear the(111)crystal plane and perhaps with either a grownoxide overlayer or native oxide layer,which,when preparedappropriately,contains a large number of separated monatomicsteps and atomically smooth terraces between them.3.1.4 x-y displacement stage,nmechanical means used tomove a probe with respect to a surface(or vice versa)along thetwo coordinate axes in the plane of the surface.3.1.5 z-magnification(alternatively,z-sensitivity or z-scale),nterm that describes the sensitivity of the output of a surfaceprofiling instrument to displacements in the z-direction.4.Significance and Use4.1 Careful use of this practice can yield calibratedz-magnifications traceable to the SI unit of length with uncer-tainties(k=2)of approximately 7%over height ranges ofapproximately 1 nm.5.Calibration Specimen5.1 The physical step height specimen is the vicinal Si(111)surface(see Fig.1),defined in 3.1.3,containing numerousmonatomic steps,having on average a calibrated step heightvalue.The calibrated value has been traditionally assigned tobe 314 pm based on X-ray value of lattice parameter of bulksilicon(1).However,recent analysis(2-7),also taking intoaccount independent measurements by other sources,has1This test method is under the jurisdiction of ASTM Committee E42 on SurfaceAnalysis and is the direct responsibility of Subcommittee E42.14 on STM/AFM.Current edition approved Nov.1,2006.Published November 2006.2Available from International Organization for Standardization(ISO),1 rue deVaremb,Case postale 56,CH-1211,Geneva 20,Switzerland,http:/www.iso.ch.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.Copyright by ASTM Intl(all rights reserved);Sat Aug 16 02:28:24 EDT 2008Downloaded/printed byNational Taiwan University pursuant to License Agreement.No further reproductions authorized.produced a current recommended value of 312+12 pm(k=2).The difference is small in comparison with other sources ofuncertainty in the procedures for measuring sub-nanometerlevel surface topography.Future measurements using advanc-ing technology will likely produce further changes in therecommended value and reduction in its uncertainty.6.Apparatus6.1 The procedure is suitable for instruments,such as theatomic force microscope(AFM),