Background Statement for SEMI Draft Document #5471 Reapproval of SEMI E , GUIDE FOR MEASUREMENT SYSTEM ANALYSIS (MSA)

Transcription

1 Backgrund Statement fr SEMI Draft Dcument #5471 Reapprval f SEMI E , 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 E 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 E 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) /mtran@semi.rg Michael Tran (SEMI NA) /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.

2 San Jse, CA Date: 8/9/01 SEMI Draft Dcument #5471 Reapprval f SEMI E , 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 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 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 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

3 San Jse, CA 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 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 A Statistics Vcabulary and Symbls Part 1: Prbability and General Statistical Terms ISO 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 Abbreviatins and Acrnyms AIAG Autmtive Industry Actin Grup 5.3. ANOVA Analysis f Variance CRM Certified Reference Material CV Cefficient f Variatin GRR Gauge Repeatability and Reprducibility 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: ; Fax: ; ISO standards are available in the United States thrugh the American Natinal Standards Institute, 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

4 San Jse, CA Date: 8/9/ LSL Lwer Specificatin Limit MS Measurement System MSA Measurement System Analysis P/T Precisin-t-Tlerance RSS Rt Sum f Squares SNR Signal t-nise Rati USL Upper Specificatin Limit VIM Internatinal Vcabulary f Basic and General Terms in Metrlgy 5.4 Definitins 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 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 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 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) 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 Discussin The purpse f calibratin is t reduce r eliminate bias in the MS 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 cefficient f variatin (CV) ppulatin standard deviatin expressed as a percentage f the mean value 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

5 San Jse, CA Date: 8/9/ 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 fixed effect variable fr which estimates f the mean are btained fr each level randm effect variable fr which estimates f the mean are nt btained fr each level; rather the variable is treated as a variance cmpnent 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 ] crssed factr(s) tw factrs are crssed when every level f ne factr appears with every level f the secnd factr fixed factr factr that has either all f its levels represented in an experiment r levels selected by a nnrandm prcess 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 randm factr factr that has randmly sampled levels frm a ppulatin f levels gage alternate spelling f gauge gauge instrument used t assign a value t a quantitative r qualitative characteristic f a physical entity r phenmenn interactin effect fr which the apparent influence f ne factr n the respnse variable depends upn ne r mre ther factrs [ISO ] level value f a factr (in a designed experiment) [adapted frm ISO ]. Als called setting f a variable linearity absence f changes in variability r bias as measurements are made at different pints within the measurement range 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 lwer specificatin limit (LSL) value f an attribute belw which a prduct is said t be nncnfrming matching tlerance ( m ) difference in bias fr any tw measurement systems (MSs) f the same kind made under the cnditins f reprducibility measurand particular attribute f a phenmenn, bdy r substance subject t measurement. [VIM] measurement reslutin, f a gauge smallest difference in measurand that can be meaningfully distinguished by the gauge measurement subsystem any set f entities, prcesses, r cnditins that share a cmmn purpse in the measurement 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 measurement system (MS) all entities, prcedures, and cnditins that can influence the test result btained with a given measurement prcess 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 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

6 San Jse, CA Date: 8/9/ nested design experimental design in which different levels f ne factr appear in each level f a secnd factr ppulatin standard deviatin () square rt f the ppulatin variance ppulatin variance ( ) measure f dispersin assciated with a ppulatin distributin Discussin Fr cntinuus distributins, the ppulatin variance is the secnd central mment precisin general estimatr f the variability f a measurement prcess abut the mean value f the test results btained 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 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) 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 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 Discussin The term independent variable is nt recmmended as a synnym due t ptential cnfusin with independence 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 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 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 repeatability ( r ) variability assciated with repeated measurements taken under repeatability cnditins 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 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 reprducibility ( R ) variability assciated with the measurement system (MS) when measurements are made under different (but typical) cnditins 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

7 San Jse, CA Date: 8/9/01 R (3) 1 3 q and they may be separated by the use f judiciusly designed experiments respnse variable variable representing the utcme f a designed experiment. Als called utput variable Discussin The term dependent variable is nt recmmended as a synnym due t ptential cnfusin with independence rt sum f squares (RSS) difference square rt f the difference f the squares f tw numbers rt sum f squares (RSS) sum square rt f the sums f the squares f tw r mre numbers sample standard deviatin (s) square rt f the sample variance sample variance (s ) measure f dispersin given by the average squared deviatin frm the mean fr a set f numbers 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 signal t-nise rati (SNR) rati f the variatin in the manufactured prduct t the precisin f the measurement system (MS) 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 stability absence f additinal variability due t taking measurements ver time (typically several days r lnger) statistical mdel mathematical functin relating ne r mre variables t knwn and measurable inputs plus ne r mre unknwn stchastic (errr) terms 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

8 San Jse, CA 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) tlerance abslute magnitude f the full range f the prduct specificatin ttal variance ( Ttal ) sum f the prduct variance and the square f the reprducibility uncertainty parameter, assciated with a measurement, that characterizes the dispersin f values that can be reasnably attributed t the bject being measured 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 upper specificatin limit (USL) value f an attribute abve which a prduct is said t be nncnfrming variable quantitative r qualitative characteristic f an bject, prcesses, r state that may take n mre than ne value Discussin When the values ccur unpredictably, it is a randm variable 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