ASTM_E_2246_-_11e1.pdf

Designation:E2246111Standard Test Method forStrain Gradient Measurements of Thin,Reflecting FilmsUsing an Optical Interferometer1This standard is issued under the fixed designation E2246;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()indicates an editorial change since the last revision or reapproval.1NOTEReference(1)was editorially revised in September 2013.1.Scope1.1 This test method covers a procedure for measuring thestrain gradient in thin,reflecting films.It applies only to films,such as found in microelectromechanical systems(MEMS)materials,which can be imaged using an optical interferometer,also called an interferometric microscope.Measurements fromcantilevers that are touching the underlying layer are notaccepted.1.2 This test method uses a non-contact optical interfero-metric microscope with the capability of obtaining topographi-cal 3-D data sets.It is performed in the laboratory.1.3 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 Documents2.1 ASTM Standards:2E2244 Test Method for In-Plane Length Measurements ofThin,Reflecting Films Using an Optical InterferometerE2245 Test Method for Residual Strain Measurements ofThin,Reflecting Films Using an Optical InterferometerE2444 Terminology Relating to Measurements Taken onThin,Reflecting FilmsE2530 Practice for Calibrating the Z-Magnification of anAtomic Force Microscope at Subnanometer DisplacementLevels Using Si(111)Monatomic Steps(Withdrawn2015)32.2 SEMI Standard:4MS2 Test Method for Step Height Measurements of ThinFilms3.Terminology3.1 Definitions:3.1.1 The following terms can be found in TerminologyE2444.3.1.2 2-D data trace,na two-dimensional group of pointsthat is extracted from a topographical 3-D data set and that isparallel to the xz-or yz-plane of the interferometric micro-scope.3.1.3 3-D data set,na three-dimensional group of pointswith a topographical z-value for each(x,y)pixel locationwithin the interferometric microscopes field of view.3.1.4 anchor,nin a surface-micromachining process,theportion of the test structure where a structural layer is inten-tionally attached to its underlying layer.3.1.5 anchor lip,nin a surface-micromachining process,the freestanding extension of the structural layer of interestaround the edges of the anchor to its underlying layer.3.1.5.1 DiscussionIn some processes,the width of theanchor lip may be zero.3.1.6 bulk micromachining,adja MEMS fabrication pro-cess where the substrate is removed at specified locations.3.1.7 cantilever,na test structure that consists of a free-standing beam that is fixed at one end.3.1.8 fixed-fixed beam,na test structure that consists of afreestanding beam that is fixed at both ends.3.1.9 in-plane length(or deflection)measurement,ntheexperimental determination of the straight-line distance be-tween two transitional edges in a MEMS device.3.1.9.1 DiscussionThis length(or deflection)measure-ment is made parallel to the underlying layer(or the xy-planeof the interferometric microscope).1This test method is under the jurisdiction of ASTM Committee E08 on Fatigueand Fracture and is the direct responsibility of Subcommittee E08.05 on CyclicDeformation and Fatigue Crack Formation.Current edition approved Nov.1,2011.Published January 2012.Originallyapproved in 2002.Last previous edition approved in 2005 as E2246 05.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.4For referenced Semiconductor Equipment and Materials International(SEMI)standards,visit the SEMI website,www.semi.org.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 3.1.10 interferometer,na non-contact optical instrumentused to obtain topographical 3-D data sets.3.1.10.1 DiscussionThe height of the sample is measuredalong the z-axis of the interferometer.The x-axis is typicallyaligned parallel or perpendicular to the transitional edges to bemeasured.3.1.11 MEMS,adjmicroelectromechanical systems.3.1.12 microelectromechanical systems,adjin general,this term is used to describe micron-scale structures,sensors,actuators,and technologies used for their manufacture(such as,silicon process technologies),or combinations thereof.3.1.13 residual strain,nin a MEMS process,the amountof deformation(or displacement)per unit length constrainedwithin the structural layer of interest after fabrication yetb