ASTM_F_1617_-_98.pdf

Designation:F 1617 98Standard Test Method forMeasuring Surface Sodium,Aluminum,Potassium,and Ironon Silicon and EPI Substrates by Secondary Ion MassSpectrometry1This standard is issued under the fixed designation F 1617;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 covers the determination of totalsodium,aluminum,potassium,and iron on the surface ofmirror-polished single crystal silicon and silicon epi substratesusing secondary ion mass spectrometry(SIMS).This testmethod measures the total amount of each metal,because thistest method is independent of the metals chemistry or electri-cal activity.1.2 This test method can be used for silicon with all dopantspecies and dopant concentrations.1.3 This test method is especially designed to be used forsurface metal contamination that is located within approxi-mately 5 nm of the surface of the wafer.1.4 This test method is especially useful for determining thesurface metal areal densities in the native oxide or chemicallygrown oxide of polished silicon substrates after cleaning.1.5 This test method is useful for sodium,aluminum,potassium,and iron areal densities between 109and1014atoms/cm2.The limit of detection is determined by eitherthe BLANK value or by count rate limitations,and may varywith instrumentation.1.6 This test method is complementary to:1.6.1 Total reflection X-ray fluorescence(TXRF),that candetect higher atomic number Z,surface metals such as iron,butdoes not have useful(1011atoms/cm2)detection limits forsodium,potassium,and aluminum on silicon.1.6.2 Electron spectroscopy for chemical analysis and Au-ger electron spectroscopy that can detect metal surface arealdensities down to the order of 1012to 1013atoms/cm2.1.6.3 Vapor phase decomposition(VPD)of surface metalsfollowed by atomic absorption spectroscopy(AAS)or induc-tively coupled plasma mass spectrometry(ICP-MS)of theVPD residue,where the metal detection limits are 108to 1010atoms/cm2.There is no spatial information available and theVPD preconcentration of metals is dependent upon the chem-istry of each metal.1.7 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 122 Practice for Choice of Sample Size to Estimate aMeasure of Quality for a Lot or Process2E 673 Terminology Relating to Surface Analysis33.Terminology3.1 All terms in this test method are in conformance withthose given in Terminology E 673.4.Summary of Test Method4.1 Specimens of mirror-polished single crystal silicon areloaded into a sample holder.The holder is transferred into theanalysis chamber of the SIMS instrument.4.2 A primary ion beam,typically O2+,is used to bombardeach specimen with a sputter rate less than 0.015 nm/s(0.9nm/min).4.3 The area of analysis may be different for differentinstruments and may range from 100 m 3 100 m to 1mm 3 1 mm.4.4 Depending upon instrumentation,a molecular oxygenjet or leak may be focused on the analysis area.4.5 The positive secondary ions23Na,27Al,39K,and54Feare mass analyzed by a mass spectrometer,and detected by anelectron multiplier(EM)or equivalent high-sensitivity iondetector as a function of time until the signals reach back-ground levels or 1%of the initial signal rates of each element.The instrumentation must be able to discriminate the elementalion signals from molecular interferences.4.6 A BLANK silicon sample is used to evaluate whetherthe lower limit of detection arises from molecular ion interfer-ences,elemental instrumental backgrounds,or count ratelimitations.The matrix positive secondary ion count rate forsilicon(28Si,29Si,or30Si)is measured by a faraday cup(FC)or appropriate detector during,or at the end of,the profile.If1This test method is under the jurisdiction of ASTM Committee F-1 onElectronics and is the direct responsibility of Subcommittee F01.06 on SiliconMaterials and Process Control.Current edition approved May 10,1998.Published July 1998.Originallypublished as F 1617-95.Last previous edition F 1617-95.2Annual Book of ASTM Standards,Vol 14.02.3Annual Book of ASTM Standards,Vol 03.06.1AMERICAN SOCIETY FOR TESTING AND MATERIALS100 Barr Harbor Dr.,West Conshohocken,PA 19428Reprinted from the Annual Book of ASTM Standards.Copyright ASTMmultiple detectors are used during the test,the relative sensi-tivities of the detectors are determined by measuring standardion signals(either the same positive secondary ion count rate orion count rates of known relative intensity such as natural28Si/30Si)on each detector.4.7 The net integrated23Na,2