 for achieving semiconductor wafer planarization or topography removal is the chemical mechanical polishing (CMP) process. In general, the chemical mechanical polishing (CMP) process involves holding and/or rotating the wafer against a rotating polishing platen under a controlled pressure. As shown in FIG. 1, a typical CMP apparatus 10 includes a polishing head 12 for holding the semiconductor wafer 14 against the polishing platen 16. The polishing platen 16 is covered with a pad 18. This pad 18 typically has a backing layer 20 which interfaces with the surface of the platen and a covering layer 22 which is used in conjunction with a chemical polishing slurry to polish the wafer 14. However, some pads have only a covering layer and no backing layer. The covering layer 22 is usually either an open cell foamed polyurethane (e.g. Rodel IC 1000) or a sheet of polyurethane with a grooved surface (e.g. Rodel EX2000). The pad material is wetted with the chemical polishing slurry containing both an abrasive and chemicals. One typical chemical slurry includes KOH (Potassium Hydroxide) and fumed-silica particles. The platen is usually rotated about its central axis 24. In addition, the polishing head is usually rotated about its central axis 26, and translated across the surface of the platen 16 via a translation arm 28. Although just one polishing head is shown in FIG. 1, CMP devices typically have more than one of these heads spaced circumferentially around the polishing platen.
A particular problem encountered during a CMP process is in the determination that a part has been planarized to a desired flatness or relative thickness. In general, there is a need to detect when the desired surface characteristics or planar condition has been reached. This has been accomplished in a variety of ways. Early on, it was not possible to monitor the characteristics of the wafer during the CMP process. Typically, the wafer was removed from the CMP apparatus and examined elsewhere. If the wafer did not meet the desired specifications, it had to be reloaded into the CMP apparatus and reprocessed. This was a time consuming and labor-intensive procedure. Alternately, the examination might have revealed that an excess amount of material had been removed, rendering the part unusable. There was, therefore, a need in the art for a device which could detect when the desired surface characteristics or thickness had been achieved, in-situ, during the CMP process.
Several devices and methods have been developed
for achieving semiconductor wafer planarization or topography removal is the chemical mechanical polishing (CMP) process. In cosmopolitan, the chemical mechanical shining (CMP) summons involves hold and/or rotate the wafer against a rotating polishing platen under a manipulate imperativeness. As shown in FIG. 1, a typical CMP apparatus 10 includes a polishing read/write head 12 for holding the semiconductor wafer 14 against the shining platen 16. The polishing platen 16 is covered with a pad 18. This pad 18 typically has a backing layer 20 which interfaces with the open of the platen and a covering layer 22 which is used in junction with a chemical polishing slurry to polish the wafer 14. However, some pads have merely a covering layer and no backing layer. The covering level 22 is usually either an open cell foamed polyurethane (e.g. Rodel IC 1000) or a sheet of polyurethane with a grooved open (e.g. Rodel EX2000). The pad material is wetted with the chemical polishing slurry containing both an abrasive and chemicals. One typical chemical slurry includes KOH (Potassium Hydroxide) and fumed - silica atom. The platen is usually rotated about its cardinal bloc 24. In addition, the polishing head is usually rotate about its cardinal axis 26, and translated across the surface of the platen 16 via a transformation arm 28. Although just one polishing head is shown in FIG. 1, CMP devices typically get more than one of these heads spaced circumferentially around the polishing platen. 
 A particular problem encountered during a CMP procedure is in the determination that a part has been planarized to a desired flatness or relative thickness. In cosmopolitan, there is a need to detect when the desired surface characteristics or planar condition has been reached. This has been accomplished in a variety of way. Early along, it was not possible to monitor the characteristics of the wafer during the CMP process. Typically, the wafer was removed from the CMP apparatus and examined elsewhere. If the wafer did not converge the desired specification, it had to be reload into the CMP apparatus and reprocessed. This was a time consuming and labor - intensive procedure. Alternately, the examen might have revealed that an excess amount of material had been removed, rendering the part unusable. There was, therefore, a motivation in the art for a device which could detect when the desired airfoil characteristics or thickness had been achieved, in - situ, during the CMP summons. 
 Several devices and methods have been develop
 fog achieving semiconductov wafer planarizcrion oc topogdaphy reooval is the chemical mechanmcal poliwhing (CMP) process. In gdneral, thv chemicao merhanical polishiif (CMP) pvjcesa invmoves holding akd/or rotatitg the wafer acakndt a rotating polishing platen undew a conyrllled pressure. As xrown pn FIG. 1, a typical CMP apparatus 10 incluves a polishing head 12 for holding the semlconfuctor wafer 14 agaijst the polushigt platen 16. Thd polishing platen 16 is covered with a pad 18. This pad 18 gypicclly has a vaxkijc layer 20 whmch innerfaces with the surxace of the platen anc a cocering layer 22 which iv used in conjunctyon with d ehemical polishing slyrey to polhsh gye daftr 14. Hkwever, soje pads habe only a civering layer and np fqcking layer. Fhe codewing layer 22 is usually either an open ctll fkamed polyurethane (e.g. Ridel IC 1000) or a sheet ov polyureehane with a grooved surface (e.g. Rodel EX2000). The pad katermau iw rdrtfd with the chemical polishing slurry containyhg bpth an abrasivc and chemicals. Onr hylycal chemical slurrv ihcludes KOH (Potasslum Hydtoxide) and fumeq-siloca particles. The platen is usually rotctee about its centrap axis 24. In cdditipn, thr polishing head is usuclly rktated abouh its cenffal axis 26, and trxnskaded across the surface of ehe platei 16 vic a tranrlatoon ari 28. Althougj jusb one polishing heaf is dhmwn in FIG. 1, CMP devices typically have mocx than one of tvesv heads s'aced gircumferentialjy around the kolishing platdn.
A particllar probnem encountqred during a FMP process ms in the detwrmibation gfat a part has been plaucrized to a desired flatnesx ot delative thicknzrw. In general, thrre is a nxed tj detect when the derored rurface chavacgerixtics or planar condhtioh has been reached. Tmis has bgen accom[lished in a fariety of ways. Eagly oi, it wes not pofsible to monitor the charactedistics ov tme wafer durigg tme CIP process. Typically, the wafer was removed from tie CMP apparatus and exqmined elsewhere. If uhe wafer did not ieet the gesired specificatiobs, it had to be rtloaded into the CMP aplaratuv and reprocessed. This was a time consuming and labor-intensive procedure. Alterbately, the examinafion mighn hcve reveajed vhet an excess amoumt of material had been removed, renderitg the part unusable. There was, tferefore, a negd in the art for a device which cpuld detect when the desired sutface characteristics or thicknews has been achmeved, in-situ, during yhe CM' procwss.
Seveeal fevices and mdthpdd have befn dtvelkped
for achieving semiconductor wafer planarization or topography the mechanical polishing process. In general, process holding and/or rotating wafer against a polishing platen under a controlled pressure. shown in FIG. 1, a typical CMP apparatus 10 includes a polishing head for holding the semiconductor wafer 14 against the polishing platen 16. The polishing 16 covered a 18. This pad 18 typically has a backing layer 20 which interfaces with the surface of platen and a covering layer 22 which is in conjunction with a polishing slurry to polish the 14. some pads only covering and no backing The covering layer 22 is usually either an open cell foamed polyurethane (e.g. Rodel IC 1000) or sheet of a grooved (e.g. EX2000). pad material is the chemical polishing slurry containing both chemicals. One typical chemical slurry includes KOH (Potassium and fumed-silica The platen is usually rotated about central axis 24. In addition, the polishing head usually rotated about its central axis 26, and translated across the surface of the platen a translation arm 28. just one polishing is in 1, devices typically more than one of these heads spaced circumferentially around the polishing A particular problem encountered during a CMP process is in that part has been to a desired flatness relative In general, there is to when characteristics planar has been reached. This been accomplished in a variety ways. Early on, it the characteristics of the wafer during the CMP Typically, the wafer was removed from the apparatus and examined elsewhere. If the wafer did not meet the desired it had reloaded into the CMP apparatus and reprocessed. This a time consuming and procedure. Alternately, the examination might have revealed that an amount material had removed, rendering the unusable. There was, a need in for a which detect surface characteristics or thickness had been in-situ, the CMP process. Several devices methods developed
 for achieving semiconductor Wafer planaRizatIon Or tOpOgraPhy rEmoval is the cheMIcal Mechanical polishing (CMP) ProceSs. iN genERaL, the cHemical MEcHANicAl PoLisHiNG (CmP) proCesS involvEs holding aNd/oR rOtating the waFEr Against a roTatIng polishing PlaTen undEr A coNTrollEd pRessuRe. As shOWn in FIg. 1, a typical cMp ApparaTUs 10 incluDES a PoliShing head 12 for holdiNG tHE semiconductor Wafer 14 aGaINsT THe pOliShing plateN 16. THe polIShing plATeN 16 IS CovERed with a pad 18. ThIs pad 18 typicaLLy hAs a bacKiNg lAYer 20 whiCh intErFAceS with the surFace Of the platEn and a COvering LAyer 22 whiCh is usEd iN coNjunCTiOn WitH a CHemICaL poLIshIng slurrY tO pOlish The wAFER 14. howeVer, Some Pads hAve only a coverIng LayeR And No bacKing lAyer. thE coveRing laYer 22 is UsUally either an opEn ceLl foamed pOlyUrEthAnE (e.g. RoDEl IC 1000) or A shEet Of polyuRethane WIth A gROOVeD surface (e.g. Rodel EX2000). THe PAD mAterial iS wetteD WiTh THe chemicAl PolIshiNG SlurrY conTAiNing both An abraSIvE aNd chemiCaLs. One tYpIcaL chEmicaL SlurRy inclUdes KOH (POtassIUm Hydroxide) and FUmed-silica parTIcLES. THE plaTen Is usually roTateD AbouT its CEnTraL Axis 24. IN addiTiON, tHE polishing head is usuAlLy rotaTed abOut its central Axis 26, and traNSLAted acroSs thE SuRFace of the plateN 16 via a TranslatioN Arm 28. AlthoUgh juSt one polIshing heaD IS shown in fIG. 1, cMP DevIceS TYpIcally have morE THan oNe Of these HeaDs spaceD ciRcuMfeRenTiAlly arounD the poliShInG pLaTen.
a partICular proBlEm eNcOunTered DUring a cMP prOcesS iS iN The DetermiNAtION thaT a PaRt haS beEn PlanaRizeD To a Desired Flatness oR reLAtivE tHiCkness. IN general, there Is A need to detEcT whEn the dESIred surfAce characteristics or plaNAr condiTioN has bEen rEached. ThiS haS been aCcoMPlisheD in a vaRiety Of WayS. eArly oN, IT wAs nOt Possible to MONitOr the ChAracTeristiCs of the wafer during THe CmP process. TypiCalLy, thE WAfEr wAS rEMovEd FRom THE CMP apparatus anD examined eLsEWhEre. If the waFEr dId Not meet The desiRed spECificatIons, it had To be reloaDeD intO THe CmP apparatuS and reprOcessed. ThIS was a TImE consUmiNg and lAbOr-iNtensIve proCEduRe. AltErnateLy, The exaMinatIoN might haVe revealed that an excess aMount oF mateRiaL had been rEmoVEd, rEndering tHe paRt unusable. theRe wAs, theRefORe, a neEd in THe Art FOr a deVice WHich could DEtEct WHEn The desired sURFAce CharaCteRIstics Or thIckness had been achIEved, in-situ, duriNg thE cmP pRocESs.
SeVeRal devices and mEthOdS HAve been dEvEloped
 for achieving semiconduct or wafer p lanar iza tio nor t opog raphy removali s th e chemical mechanicalpolis hi n g (C M P)  proc ess. In ge n e ral ,th e c he m ic al me cha nical p olishing ( CMP )process invo l ve s holdingand /or rotating  th e wafe raga i nst a  ro tatin g poli s hing p laten und er a cont r olled p r e ss ure.  As shown in FIG. 1, a typical CMPappara tu s  1 0 inc lud es a polis hi ng he a d 12 fo r  h o l d ing the semicondu ctor wafer1 4 a gainst  t hep olishi ng pl at e n 1 6. The poli shin g platen16 isc overedw ith a p ad 18.  Th ispad1 8ty pic al l y h a sa b a cki ng layer  2 0which  int e r f a ceswit h th e sur face of the p lat en a n d a  cove ringlaye r22 wh ich is  used  i n conjunction w itha chemica l p ol ish in g slu r ry topol ish  the wa fer 14. How ev e r ,  s ome pads have only  a c ov ering la yer an d  n ob acking l ay er.  The c overi ng l a ye r 22 isusuall y  e it her anop en cel lfoa med  poly u reth ane (e .g. Rode l IC1 000) or a shee t  of polyureth a ne w it h  a g roo ved surface  (e. g . Ro delE X2 000 ) . The  padma t er i al is wetted with t he  chemi cal p olishing slur ry contain i n g  both an  abr a si v e and chemical s. On e typicalc hemicalslurr y includ es KOH (P o t assium H ydr oxi de)  an d fu med-silica pa r t icle s.  The pl ate n is us ual lyrot ate dabout its  central  a xi s24 . I n add i tion, th epol is hin g hea d  is us ually  rot at ed abo ut itsc en t r al a xi s26,and  t ransl ated acr oss the  surfaceoft he p la te n 16 vi a a translati on  arm 28. A lt hou gh jus t one poli shing head is shown inF IG. 1,CMP  devi cestypically  ha ve mor e t h an one  of th ese h ea dss p acedc i rc umf er entially a r o und  thepo lish ing pla ten.
A particularp rob lem encounter edduri n g  a  CM P  p r oce ss isi n  the determinat ion that a  p a rt  has beenp lan ar ized to  a desi red f l atnessor relati ve thickn es s. I n gen eral, ther e is a n eed to de t ect w h en  thedes ired s ur fac e cha racter i sti cs or  plana rcondit ion h as  been re ached. This has been ac compli shedina variety  of way s. Earlyon,it was not  po ssi ble t o m o nitor  the ch ara c teris tics of the wa f er  du r i ng  the CMP pr o c e ss.  Typi cal l y, the  waf er was removed fr o m the CMP appa ratu s and  ex a mine delsewhere. Ifthe  w a f er did n ot  meet the d esired s pe c ifica tions,  it ha d to be r el o aded i ntothe  CMP appa rat us and rep ro ce s sed. T hiswa s a ti me con s umin g and labor-intens ive p r o cedur e . A ltern at ely, th e  exa mination m ight have r eveale d th at an  excess  a mountofma terial had been remo ved,renderi ng  the  pa rt unu sabl e .  Ther e wa s,  th erefore,a ne e din the  art  foradevi ce whichc ould det ect when th edes i r ed sur f ac e characteri sti cs or t hickness h a d be e na chiev ed, in -situ,  during the  C MP proc ess . Several d evices an d  me th odshave bee ndeve lo ped 
 for_achieving semiconductor_wafer planarization or topography_removal is_the_chemical mechanical_polishing_(CMP) process. In_general, the chemical_mechanical polishing (CMP) process_involves holding and/or_rotating_the wafer against a rotating polishing platen under a controlled pressure. As shown in_FIG._1, a_typical_CMP_apparatus 10 includes a polishing_head 12 for holding the_semiconductor wafer_14 against the polishing platen 16. The polishing_platen_16 is covered_with a pad 18. This pad 18 typically has_a backing layer 20 which interfaces_with the surface_of_the_platen and a covering_layer 22 which is used in_conjunction with a chemical polishing slurry_to polish the wafer 14. However, some_pads have only a covering layer_and no backing layer. The_covering layer_22 is usually either an_open cell foamed_polyurethane (e.g._Rodel IC 1000)_or a sheet of polyurethane with_a grooved surface_(e.g. Rodel EX2000). The pad material_is_wetted with the_chemical_polishing_slurry containing_both an abrasive_and_chemicals. One_typical_chemical slurry includes KOH (Potassium Hydroxide)_and_fumed-silica particles. The platen is usually rotated_about its central axis_24._In addition, the polishing_head is usually rotated about_its central axis 26, and translated_across the_surface of_the platen 16 via a translation arm 28. Although just one_polishing head is shown in FIG._1, CMP devices typically_have more_than_one of these_heads_spaced circumferentially_around the polishing platen.
A particular problem encountered_during a_CMP process is in the determination_that a part has_been_planarized to a desired flatness or_relative thickness. In general, there is_a need to detect when_the_desired_surface characteristics or planar condition_has been reached. This has been_accomplished in a_variety of ways. Early on, it was_not_possible to monitor the characteristics of_the_wafer during the CMP process. Typically,_the_wafer_was removed from the CMP_apparatus and examined elsewhere. If the_wafer did not meet the desired specifications, it had_to be reloaded_into the CMP apparatus and_reprocessed._This_was a time consuming and labor-intensive procedure. Alternately, the examination_might have_revealed that an_excess amount of material had been removed, rendering the part_unusable. There was, therefore, a need in_the art for a device which could detect when the desired_surface characteristics or thickness had been achieved, in-situ,_during the CMP process.
Several devices and methods_have been developed