Backgrund Statement fr SEMI Draft Dcument #5471 Reapprval f SEMI E89-0707, GUIDE FOR MEASUREMENT SYSTEM ANALYSIS (MSA) Ntice: This backgrund statement is nt part f the ballted item. It is prvided slely t assist the recipient in reaching an infrmed decisin based n the ratinale f the activity that preceded the creatin f this Dcument. Ntice: Recipients f this Dcument are invited t submit, with their cmments, ntificatin f any relevant patented technlgy r cpyrighted items f which they are aware and t prvide supprting dcumentatin. In this cntext, patented technlgy is defined as technlgy fr which a patent has issued r has been applied fr. In the latter case, nly publicly available infrmatin n the cntents f the patent applicatin is t be prvided. Backgrund SEMI E89-0707 is due fr Five Year Review. This prcess is required by the SEMI Regulatins t ensure that this standard is still valid. At the SEMICON West 01 Standards Meetings, the NA Metrics Cmmittee apprved the letter ballt distributin fr the reapprval f SEMI E89-0707. This technical ballt is intended fr the reapprval f SEMI E89 and des nt present any technical changes t the afrementined dcument. Review and Adjudicatin Infrmatin Task Frce Review Cmmittee Adjudicatin Grup: NA Metrics Cmmittee NA Metrics Cmmittee Date: Octber 31, 01 Octber 31, 01 Time & Timezne: 3:00 PM - 6:00 PM Nn Pacific Time 3:00 PM - 6:00 PM Nn Pacific Time Lcatin: SEMI Headquarters SEMI Headquarters City, State/Cuntry: San Jse, Califrnia San Jse, Califrnia Leader(s): David Buldin (david.buldin@sbcglbal.net) David Buldin (david.buldin@sbcglbal.net) Mark Frankfurth (Mark_Frankfurth@Cymer.cm) Mark Frankfurth (Mark_Frankfurth@Cymer.cm) Standards Staff: Michael Tran (SEMI NA) 408.943.7019 /mtran@semi.rg Michael Tran (SEMI NA) 408.943.7019 /mtran@semi.rg This meeting s details are subject t change, and additinal review sessins may be scheduled if necessary. Cntact Standards staff fr cnfirmatin. Telephne and web infrmatin will be distributed t interested parties as the meeting date appraches. If yu will nt be able t attend these meetings in persn but wuld like t participate by telephne/web, please cntact Standards staff.
San Jse, CA 95134-17 Date: 8/9/01 SEMI Draft Dcument #5471 Reapprval f SEMI E89-0707, GUIDE FOR MEASUREMENT SYSTEM ANALYSIS (MSA) NOTICE: This ballt cntains nly the fllwing sectins f the standard being prpsed fr Reapprval: Purpse, Scpe, Limitatins, Referenced Standards and Dcuments, and Terminlgy. If yu wuld like a cpy f SEMI E89 in rder t vte n it, please request a cpy by email frm Michael Tran mtran@semi.rg at least three business days befre the vting deadline. 1 Purpse 1.1 The purpse f this guide is t prvide a cnsistent set f terminlgy and describe a simplified, but cnstructive, experimental apprach t planning and perfrming a measurement system analysis (MSA). 1. The gal f an MSA is t characterize the perfrmance capability f the measurement system (MS) as it is intended t be used in a manufacturing r labratry setting. 1..1 Accurately identifying the MS bias and the size and nature f all surces f variability allws ne t determine whether the MS is capable f perfrming its intended functin. Mrever, a well-designed MSA can be used t identify and quantify areas that need the mst imprvement. Scpe.1 This guide cvers prcedures fr determining specific measures f MS capability including: measurement variability (i.e., reprducibility) under a variety f cnditins, including effects f repeatability, lad-unlad, and time, and bias, including bias-related linearity, stability, and matching tlerance.. This guide als cvers secndary metrics such as precisin-ver-tlerance (P/T) rati and signal-t-nise rati (SNR)..3 The primary fcus f this guide is n determining measurement capability f autmated wafer MSs under nrmal perating cnditins, but the definitins and methdlgies are extendible t many ther measurement situatins invlving autmated measurements n units such as prcessed dice, packaged devices, flat panel displays, piece parts, etc..4 While there is n universally accepted crrect way t cnduct an MSA, the apprach described in this dcument is supprted in the technical literature (see 11) and cngruent with practices advcated in ISO 575-. The prcedures given in this guide represent an apprach t the cnduct f an MSA and prvide basic reference methds that shuld serve fr a variety f applicatins. Other methds may be apprpriate in certain circumstances..5 The prcedures in this guide that are intended t separate the varius surces f nnsystematic (i.e., randm) errrs are based n the use f factrial experiments and analysis f variance (ANOVA). Because the primary fcus f this guide is n evaluatin f autmated MSs, the variability intrduced by different peratrs is expected t be minimal. NOTE 1: Infrmatin n measurement uncertainty calculatins is prvided in Related Infrmatin 1. Infrmatin n testing measurement distributins fr nrmality and equal repeatability is prvided in Related Infrmatin. Page 1
San Jse, CA 95134-17 Date: 8/9/01 NOTICE: This standard des nt purprt t address safety issues, if any, assciated with its use. It is the respnsibility f the users f this standard t establish apprpriate safety and health practices and determine the applicability f regulatry r ther limitatins prir t use. 3 Limitatins 3.1 Determinatin f MS capability is meaningless unless the MS is in cntrl. Methdlgy fr establishing and maintaining MS cntrl is beynd the scpe f this guide. Such methdlgy shuld be a part f a quality management system, such as that mandated by ISO 9000 r similar standards. Additinal guidance fr labratries withut established prcedures may be fund in the ASTM Manual n Presentatin f Data and Cntrl Chart Analysis. 1 3. This guide des nt address thse aspects f measurement uncertainty assciated with change in the bject being measured, either spatially r temprally. 3.3 This guide des nt address determinatin f measurement capability in the case f destructive measurements n samples, r when the MS alters the bject being measured as a result f making the measurement. 3.4 This guide des nt apply t inter-labratry experiments designed t measure inter-labratry precisin f test methds. 4 Referenced Standards and Dcuments 4.1 ISO Standards ANSI/ISO Z540- Guide t the Expressin f Uncertainty in Measurement ANSI/ISO/ASQC A3534-1 Statistics Vcabulary and Symbls Part 1: Prbability and General Statistical Terms ISO 3534-3 Statistics Vcabulary and Symbls Part 3: Design f Experiments ISO 575- Accuracy (trueness and precisin) f measurement methds and results Part : Basic methd fr the determinatin f repeatability and reprducibility f a standard measurement methd ISO 9000 Quality management systems Fundamentals and vcabulary, 000 NOTICE: Unless therwise indicated, all dcuments cited shall be the latest published versins. 5 Terminlgy 5.1 Terminlgy in this sectin that is nt directly used in this guide, is likely t be encuntered while cnducting an MSA. 5. Definitins f many ther terms related t metrlgy and statistics can be fund in VIM, 3 ANSI/ISO/ASQC A3534-1, and ISO 3534-3. 5.3 Abbreviatins and Acrnyms 5.3.1 AIAG Autmtive Industry Actin Grup 5.3. ANOVA Analysis f Variance 5.3.3 CRM Certified Reference Material 5.3.4 CV Cefficient f Variatin 5.3.5 GRR Gauge Repeatability and Reprducibility 5.3.6 GR&R See GRR 1 Manual n Presentatin f Data and Cntrl Chart Analysis, 6th editin, MNL 7 (ASTM Internatinal, West Cnshhcken, PA, 1991) Internatinal Organizatin fr Standardizatin, ISO Central Secretariat, 1 rue de Varembé, Case pstale 56, CH-111 Geneva 0, Switzerland. Telephne: 41..749.01.11; Fax: 41..733.34.30; http://www.is.ch; ISO standards are available in the United States thrugh the American Natinal Standards Institute, http://www.ansi.rg, and in mst ther cuntries thrugh the ISO member bdy. 3 Internatinal Vcabulary f Basic and General Terms in Metrlgy, Secnd Editin [VIM] (ISO, Genève, 1993) Page
San Jse, CA 95134-17 Date: 8/9/01 5.3.7 LSL Lwer Specificatin Limit 5.3.8 MS Measurement System 5.3.9 MSA Measurement System Analysis 5.3.10 P/T Precisin-t-Tlerance 5.3.11 RSS Rt Sum f Squares 5.3.1 SNR Signal t-nise Rati 5.3.13 USL Upper Specificatin Limit 5.3.14 VIM Internatinal Vcabulary f Basic and General Terms in Metrlgy 5.4 Definitins 5.4.1 accuracy clseness f agreement between a test result r the mean f a grup f test results made n an bject and its true value. 3 5.4.1.1 Discussin Accuracy depends n bth the precisin and bias f the measurement prcess. Since randm cmpnents f errr (resulting in imprecisin) and systematic cmpnents f errr (resulting in bias) cannt be cmpletely separated in rutine use, the reprted accuracy must be interpreted as a cmbinatin f these tw elements. 5.4. bias difference between the ppulatin mean f the test results frm a measurement prcess and the true (accepted reference) value f the prperty being measured. 5.4..1 Discussin Bias is a systematic cmpnent f measurement uncertainty. One r mre systematic errr cmpnents may cntribute t the bias. The true value and the ppulatin mean are bth unknwn. The true value may be estimated with the use f a cnsensus value. If sufficient measurements are made t adequately mitigate the effects f measurement variability, the ppulatin mean may be estimated frm the sample mean where: x = sample mean, n = number f measurements, and x i = i th measurement value. 1 x n n x i i1 (1) 5.4.3 calibratin set f peratins that establish the relatinship between values f quantities indicated by a measurement system (MS) and the crrespnding values assigned t reference materials. 5.4.3.1 Discussin The purpse f calibratin is t reduce r eliminate bias in the MS. 5.4.4 certified reference material (CRM) reference material, ne r mre f whse prperty values are certified by a technically valid prcedure, accmpanied by r traceable t a certificate r ther dcumentatin issued by a certifying bdy. 5.4.5 cefficient f variatin (CV) ppulatin standard deviatin expressed as a percentage f the mean value. 5.4.5.1 Discussin CV can be estimated frm the sample standard deviatin, s, and the sample mean, x, f a distributin as fllws: s CV 100 () x CV is an apprpriate measure f variability nly when the sample standard deviatin is prprtinal t the mean; therwise it varies with the value f the measurand. If the sample standard deviatin is independent f the value f the measurand, it is mre apprpriate t use it directly rather than CV. Page 3
San Jse, CA 95134-17 Date: 8/9/01 5.4.6 effect change in the expected value f a given respnse due t the change f a given factr frm ne level t anther. It is a measure f influence that a particular variable level has n the utput variable. 5.4.6.1 fixed effect variable fr which estimates f the mean are btained fr each level. 5.4.6. randm effect variable fr which estimates f the mean are nt btained fr each level; rather the variable is treated as a variance cmpnent. 5.4.7 factr predictr variable whse level is changed with the intent f assessing its effect n the respnse variable (in a designed experiment) [adapted frm ISO 3534-3]. 5.4.7.1 crssed factr(s) tw factrs are crssed when every level f ne factr appears with every level f the secnd factr. 5.4.7. fixed factr factr that has either all f its levels represented in an experiment r levels selected by a nnrandm prcess. 5.4.7.3 nested factr(s) factr that has a different set f levels appearing within each level f a secnd factr. Factr B is nested in factr A when randmizatin f the levels f factr B is restricted t specific levels f factr A. 5.4.7.4 randm factr factr that has randmly sampled levels frm a ppulatin f levels. 5.4.8 gage alternate spelling f gauge. 5.4.9 gauge instrument used t assign a value t a quantitative r qualitative characteristic f a physical entity r phenmenn. 5.4.10 interactin effect fr which the apparent influence f ne factr n the respnse variable depends upn ne r mre ther factrs [ISO 3534-3]. 5.4.11 level value f a factr (in a designed experiment) [adapted frm ISO 3534-3]. Als called setting f a variable. 5.4.1 linearity absence f changes in variability r bias as measurements are made at different pints within the measurement range. 5.4.1.1 Discussin Traditinal definitins f linearity ignre the fact that variability can change ver the measurement range, as well as bias. The assumptin f cnstant variability ver the measurement range shuld be verified during the MS analysis. 5.4.13 lwer specificatin limit (LSL) value f an attribute belw which a prduct is said t be nncnfrming. 5.4.14 matching tlerance ( m ) difference in bias fr any tw measurement systems (MSs) f the same kind made under the cnditins f reprducibility. 5.4.15 measurand particular attribute f a phenmenn, bdy r substance subject t measurement. [VIM] 5.4.16 measurement reslutin, f a gauge smallest difference in measurand that can be meaningfully distinguished by the gauge. 5.4.17 measurement subsystem any set f entities, prcesses, r cnditins that share a cmmn purpse in the measurement. 5.4.17.1 Discussin A measurement subsystem may cntain ne r mre f its wn subsystems. Fr example, a wafer handling mechanism may be further cmpsed f wafer lading and wafer psitining subsystems. 5.4.18 measurement system (MS) all entities, prcedures, and cnditins that can influence the test result btained with a given measurement prcess. 5.4.18.1 Discussin The MS may include, but is nt limited t, the gauge, peratrs, setup mechanics, wafers, lcatins n a wafer, envirnmental cnditins, sftware used by the gauge, measurement methd, etc. The MS may be cmprised f measurement subsystems. 5.4.19 measurement system analysis (MSA) prcedure in which relevant surces f bias and variability assciated with a measurement system (MS) are estimated. NOTE : MSA is als smetimes called gauge (r gage) repeatability and reprducibility (GRR r GR&R). Page 4
San Jse, CA 95134-17 Date: 8/9/01 5.4.0 nested design experimental design in which different levels f ne factr appear in each level f a secnd factr. 5.4.1 ppulatin standard deviatin () square rt f the ppulatin variance. 5.4. ppulatin variance ( ) measure f dispersin assciated with a ppulatin distributin. 5.4..1 Discussin Fr cntinuus distributins, the ppulatin variance is the secnd central mment. 5.4.3 precisin general estimatr f the variability f a measurement prcess abut the mean value f the test results btained. 5.4.3.1 Discussin Precisin is a randm cmpnent f measurement uncertainty. Unless the measurement prcess is in a state f statistical cntrl, the precisin f the prcess has n meaning. Since the precisin is prer fr greater dispersin f the test results, specific measures f variability (such as repeatability and reprducibility) are actually direct measures f the imprecisin f the measurement prcess. 5.4.4 precisin-t-tlerance (P/T) rati rati f the precisin f a measurement system (MS) t the tlerance (i.e., abslute magnitude f the full range f the prduct specificatin). 5.4.4.1 Discussin If the variability assciated with the measurement f a parameter by an MS is very small cmpared with the width f the specificatin range, the prbability f btaining a test result utside the specificatin limits when the value f the parameter actually lies within the specificatin limits (r cnversely) is quite small. On the ther hand, if the rati is t large, the prbability f btaining a false test result is much greater. 5.4.5 predictr variable variable that can cntribute t the explanatin f the utcme f a designed experiment. Als called input variable, descriptr variable, and explanatry variable. 5.4.5.1 Discussin The term independent variable is nt recmmended as a synnym due t ptential cnfusin with independence. 5.4.6 prduct standard deviatin ( Prduct ) ppulatin standard deviatin assciated with the distributin f values f all pssible realizatins f a prperty f an entity manufactured under specified cnditins. 5.4.6.1 Discussin The prduct variability may be estimated by taking a representative sample frm the ppulatin and calculating the sample standard deviatin (s Prduct ) taking suitable accunt f MS variatin. 5.4.7 reference material material r substance, ne r mre f whse prperty values are sufficiently hmgeneus and well established t be used fr the calibratin f a MS, fr the assessment f a measurement methd r fr assigning values t materials. 5.4.8 repeatability ( r ) variability assciated with repeated measurements taken under repeatability cnditins. 5.4.9 repeatability cnditins test cnditins invlving acquisitin f a series f test results with the same test prtcl and MS setup in the same labratry by the same peratr n the same equipment in the shrtest practical perid f time n the same test wafer withut explicit recalibratin. 5.4.9.1 Discussin The acquisitin f test data under repeatability cnditins is intended t avid influences f lng-term drift, peratr r MS differences, material variability, and the like. Recalibratin f the MS is expected t cause discntinuus differences in test results. Hwever, if recalibratin is required by the test prtcl r is internal t the MS, it is cnsidered t be an allwable variatin in determinatin f repeatability. 5.4.30 reprducibility ( R ) variability assciated with the measurement system (MS) when measurements are made under different (but typical) cnditins. 5.4.30.1 Discussin Changes assciated with subsystems r test cnditins are ptential surces f variatin t be estimated. Repeatability is ne surce f variatin. Other relevant surces f variability may include time, peratr, setup prcedure, wafer (f like variety), measurement lcatin, test instrumentatin, envirnmental cnditins, etc. Althugh the ttal number f cntributrs t the variance can be exceedingly large, ne typically fcuses n a subset that accunts fr a significant prtin f the expected MS variability. Fr clarity, the selected subset shuld be reprted tgether with the reprducibility. If q different cnditins intrduce variability int the measurement independently frm ne anther, the variances add directly Page 5
San Jse, CA 95134-17 Date: 8/9/01 R (3) 1 3 q and they may be separated by the use f judiciusly designed experiments. 5.4.31 respnse variable variable representing the utcme f a designed experiment. Als called utput variable. 5.4.31.1 Discussin The term dependent variable is nt recmmended as a synnym due t ptential cnfusin with independence. 5.4.3 rt sum f squares (RSS) difference square rt f the difference f the squares f tw numbers. 5.4.33 rt sum f squares (RSS) sum square rt f the sums f the squares f tw r mre numbers. 5.4.34 sample standard deviatin (s) square rt f the sample variance. 5.4.35 sample variance (s ) measure f dispersin given by the average squared deviatin frm the mean fr a set f numbers. 5.4.35.1 Discussin If x i is an individual measurement, x is the average acrss all measurements, and n is the number f measurements, then s 1 n 1 n i1 ( x i x) The denminatr value f n 1 is used instead f n t make the sample variance an unbiased estimatr f the ppulatin variance. 5.4.36 signal t-nise rati (SNR) rati f the variatin in the manufactured prduct t the precisin f the measurement system (MS). 5.4.36.1 Discussin Because it is difficult t directly measure the standard deviatin f the prduct withut including variatin due t the measurement instrument, SNR is generally defined as: Ttal R R SNR (5) where Ttal is an estimate f the ttal ppulatin variance btained frm apprpriate measurements f a large, representative sample f the prduct. 5.4.37 stability absence f additinal variability due t taking measurements ver time (typically several days r lnger). 5.4.38 statistical mdel mathematical functin relating ne r mre variables t knwn and measurable inputs plus ne r mre unknwn stchastic (errr) terms. 5.4.38.1 Discussin A statistical mdel cnsists f three parts. The first part is the respnse variable that is being mdeled. The secnd part is the deterministic r the systematic part f the mdel that includes predictr variables. Finally, the third part is the randm errr r stchastic part f the mdel, which can be quite elabrate. An example f a statistical mdel is: (4) where: y j p i1 x e (6) i i j y j P x i = j th measurement, = number f input variables, = i th input variable, Page 6
San Jse, CA 95134-17 Date: 8/9/01 i = its crrespnding cefficient, and e j = errr assciated with the j th measurement. In many cases the errr distributin(s) are specified befre the mdel is fit (e.g., as nrmal). 5.4.39 tlerance abslute magnitude f the full range f the prduct specificatin. 5.4.40 ttal variance ( Ttal ) sum f the prduct variance and the square f the reprducibility. 5.4.41 uncertainty parameter, assciated with a measurement, that characterizes the dispersin f values that can be reasnably attributed t the bject being measured. 5.4.41.1 Discussin Tw types f measurement uncertainty are: Type A: uncertainty cmpnents evaluated by statistical methds and Type B: uncertainty cmpnents evaluated by ther than statistical methds. 5.4.4 upper specificatin limit (USL) value f an attribute abve which a prduct is said t be nncnfrming. 5.4.43 variable quantitative r qualitative characteristic f an bject, prcesses, r state that may take n mre than ne value. 5.4.43.1 Discussin When the values ccur unpredictably, it is a randm variable. 5.4.44 variance ppulatin variance (see 5.3.). NOTICE: (SEMI) makes n warranties r representatins as t the suitability f the Standards and Safety Guidelines set frth herein fr any particular applicatin. The determinatin f the suitability f the Standard r Safety Guideline is slely the respnsibility f the user. Users are cautined t refer t manufacturer s instructins, prduct labels, prduct data sheets, and ther relevant literature, respecting any materials r equipment mentined herein. Standards and Safety Guidelines are subject t change withut ntice. By publicatin f this Standard r Safety Guideline, SEMI takes n psitin respecting the validity f any patent rights r cpyrights asserted in cnnectin with any items mentined in this Standard r Safety Guideline. Users f this Standard r Safety Guideline are expressly advised that determinatin f any such patent rights r cpyrights, and the risk f infringement f such rights are entirely their wn respnsibility. Page 7