ASTM_F_390_-_11.pdf

Designation:F39011Standard Test Method forSheet Resistance of Thin Metallic Films With a CollinearFour-Probe Array1This standard is issued under the fixed designation F390;the number immediately following the designation indicates the year of originaladoption or,in the case of revision,the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers the measurement of the sheetresistance of metallic thin films with a collinear four-probearray.It is intended for use with rectangular metallic filmsbetween 0.01 and 100 m thick,formed by deposition of amaterial or by a thinning process and supported by aninsulating substrate,in the sheet resistance range from 102to104/(see 3.1.3).1.2 This test method is suitable for referee measurementpurposes as well as for routine acceptance measurements.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 the safetyconcerns,if any,associated with its use.It is the responsibilityof whoever uses this standard to consult and establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2E2251 Specification for Liquid-in-Glass ASTM Thermom-eters with Low-Hazard Precision LiquidsF388 Method for Measurement of Oxide Thickness onSilicon Wafers and Metallization Thickness by Multiple-Beam Interference(Tolansky Method)(Withdrawn 1993)33.Terminology3.1 Definitions:3.1.1 thin filma film having a thickness much smaller thanany lateral dimension,formed by deposition of a material or bya thinning process.3.1.2 thin metallic filma thin film composed of a materialor materials with resistivity in the range from 108to 103cm.3.1.3 sheet resistance,Rs/in a thin film,the ratio ofthe potential gradient parallel to the current to the product ofthe current density and the film thickness;in a rectangular thinfilm,the quotient of the resistance,measured along the lengthof the film,divided by the length,l,to width,w,ratio.The ratiol/w is the number of squares.4.Summary of Test Method4.1 A collinear four-probe array is used to determine thesheet resistance by passing a measured direct current throughthe specimen between the outer probes and measuring theresulting potential difference between the inner probes.Thesheet resistance is calculated from the measured current andpotential values using correction factors associated with thegeometry of the specimen and the probe spacing.4.2 This test method includes procedures for checking boththe probe assembly and the electrical measuring apparatus.4.2.1 The spacings between the four probe tips are deter-mined from measurements of indentations made by the tips ina suitable surface.This test also is used to determine thecondition of the tips.4.2.2 The accuracy of the electrical measuring equipment istested by means of an analog circuit containing a knownstandard resistor together with other resistors which simulatethe resistance at the contacts between the probe tips and thefilm surface.5.Apparatus5.1 Probe Assembly:5.1.1 ProbesThe probe shaft and tip shall be constructedof tungsten carbide,Monel,hardened tool steel,or hard copperand have a conical tip with included angle of 45 to 90.Alternatively,the tip may be formed from a platinum-palladium alloy and resistance welded to the shaft.The tip shallhave a nominal initial radius of 25 to 50 m.In all cases all of1This test method is under the jurisdiction of ASTM Committee F01 onElectronics and is the direct responsibility of Subcommittee F01.17 on SputterMetallization.Current edition approved June 1,2011.Published July 2011.Originally approvedin 1973 as F390 73 T.Last previous edition approved in 2003 as F390 98(2003).DOI:10.1520/F0390-11.2For 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.3Withdrawn.THe last approved version of this historical standard is referencedon www.astm.org.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 the four paths from the electrical measurement equipmentinputs to the film surface must be identical.5.1.2 Probe ForceThe probes shall be uniformly loaded toexert a force sufficient to deform the metal film but insufficientto puncture the film.A rough guide for loading is a load of 20g/Mohs(unit of hardness)of the film material on each probe.5.1.3 Probe CharacteristicsThe probes shall be mountedin an insulating fixture such as a sapphire bearing in a methylmethacrylate or hardened polystyrene block in an equallyspaced linear array.The electrical insulation between adjacentprobe points shall b