ASTM_F_1261M_-_96_2003.pdf

Designation:F 1261M 96(Reapproved 2003)METRICStandard Test Method forDetermining the Average Electrical Width of a Straight,Thin-Film Metal Line Metric1This standard is issued under the fixed designation F 1261M;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 test method is designed for determining the averageelectrical width of a narrow thin-film metallization line.1.2 This test method is intended for measuring thin metal-lization lines such as are used in microelectronic circuits wherethe width of the lines may range from micrometres to tenths ofmicrometres.1.3 The test structure used in this test method may bemeasured while still part of a wafer,or part therefrom,or aspart of a test chip bonded to a package and electricallyaccessible by means of package terminals.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 Documents2.1 ASTM Standards:E 178 Practice for Dealing with Outlying Observations2F 1260 Test Method for Estimating Electromigration Me-dian Time-to-Failure and Sigma of Integrated CircuitMetallizations33.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 electrical linewidththe width of the line as calcu-lated by the product of the sheet resistance of the metal filmand the line length,divided by the line resistance.3.1.2 metallizationthe thin-film metallic conductor usedas electrical interconnects in a microelectronic integratedcircuit.3.1.3 test structurea passive metallization structure,withterminals to permit electrical access,that is fabricated on asemiconductor wafer by procedures used to manufacture mi-croelectronic integrated circuits.4.Summary of Test Method4.1 This test method uses a cross-bridge test structure thathas two components:One is a cross,consisting of twoperpendicularly intersecting metallization lines,which is usedto determine the sheet resistance by a van der Pauw method inwhich a forcing current,I1,through two adjacent arms to thecross,develops a voltage that is measured using the remainingtwo arms.The other component is a bridge element thatincludes the line whose width is to be determined.Two voltagetaps contact this line at a known distance from each other.Byforcing a known current,I2,through the line and measuring thevoltage difference beween the voltage taps,the mean width ofthe line can be calculated.5.Significance and Use5.1 The width of a conductor line is important to ensurepredictable timing performance of the electrical interconnectsystem,to assure control of critical device parameters,and tocontrol various processes involved in microcircuit manufac-ture.5.2 The width of a conductor line,with its thickness,definesthe cross-sectional area and therefrom the current density for agiven current.Knowledge about the current density is impor-tant in procedures for estimating reliability against degradationdue to electromigration and in the conduct of electromigrationstress tests to obtain sample estimates of the median-time-to-failure and sigma(see Test Method F 1260).6.Interferences6.1 If the four cross-resistance values(in 8.1.8)differ bymore than approximately 5%,when“wafer-level”measure-ments are made with contact probes at room temperature,thenpoor electrical contact may be the cause.Poor contacts willlead to an erroneous value for the cross resistance as well as forthe linewidth.When measurements are made at elevatedtemperatures,the differences in the four cross-resistance valueswill be larger.Good electrical contact will then be indicatedwhen the relative values of the cross resistances remain1This test method is under the jurisdiction of ASTM Committee F01 onElectronics and is the direct responsibility of Subcommittee F01.11 on Quality andHardness Assurance.Current edition approved June 10,1996.Published August 1996.Originallypublished as F 1261 89.Last previous edition F 1261 95.2Annual Book of ASTM Standards,Vol 14.02.3Annual Book of ASTM Standards,Vol 10.04.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.approximately the same with subsequent placements of thecontact probes on the same or similar structures.6.2 Measurements should be conducted in a time that isshort in comparison to any temperature changes that may occurin the metallization.If measurements are made in an environ-ment where the temperature of the metallization changes by dTbetween the time that the resistance of the cross and theresistance of the bridge line are measured,then an error ofTCR(T)dT%in the calculation of t