 object to be processed, that is to say a semiconductor wafer, is covered by a displaceable cover plate during the non-processing phases.
U.S. Pat. No. 4,687,542 describes a system for the intermediate storage of wafers where a number of wafers is arranged, accommodated in a sealed box, in a space to be evacuated, the box being opened only when the space has been sealed and evacuated.
JP-A 59-114814 describes a vacuum system in which a prevacuum pumping valve comprises a porous material which acts as a choke valve.
JP-A 61-58252 describes a specimen chamber in which the gas flow is always directed downwards during filling or evacuation of the space in order to achieve dust reduction. The aim is to prevent the stirring up of dust particles.
Even though all these means lead to a given improvement in view of dust contamination, it has been found that they are not adequate for many applications. Content addressable memory (CAM) is a special type of computer memory used in certain high speed searching applications. Unlike standard computer memory (Random Access Memory or RAM) in which the user supplies a memory address and the RAM returns the data word stored at that address, a CAM is designed such that the user supplies a data word and the CAM searches its entire memory to see if that data word is stored anywhere in it. If the data word is found, the CAM returns a list of one or more storage addresses where the word was found (in some architectures, it also returns the data word, or other associated pieces of data). Thus, a CAM may also be referred to as an associative array.
Because a CAM is designed to search its entire memory in a “single” operation, it is much faster than RAM in virtually all search applications. However, there are cost disadvantages associated with CAM. Unlike a RAM chip, which has simple storage cells, each individual memory bit in a fully parallel CAM must have its own associated comparison circuit to detect a match between the stored bit and the input bit. Additionally, match outputs from each cell in the data word must be combined to yield a complete data word match signal. The extra circuitry generally increases power dissipation since every comparison circuit is active on every clock cycle. Energy per search and search speed are two important criteria used to evaluate CAM performance. In general, two types of CAM architecture are used. A not AND (NAND)-type CAM array generally has lower power consumption, but it is generally slower because the match line is
object to be processed, that is to say a semiconductor wafer, is covered by a displaceable binding home plate during the non - processing phases. 
 U.S. Pat. No. 4,687,542 describes a organization for the intermediate storage of wafer where a number of wafers is arrange, accommodated in a sealed corner, in a space to be evacuated, the box being opened merely when the space has been sealed and evacuated. 
 JP - A 59 - 114814 describes a void system in which a prevacuum pumping valve comprises a porous fabric which acts as a choke valve. 
 JP - A 61 - 58252 describes a specimen chamber in which the gas stream is always directed downwards during filling or evacuation of the quad in order to achieve dust reduction. The aim is to prevent the stirring up of dust particles. 
 Even though all these means lead to a given improvement in view of dust contamination, it has been found that they are not adequate for many applications. Content addressable memory (CAM) is a special character of calculator memory used in certain high focal ratio searching applications. Unlike standard computer memory (Random Access Memory or RAM) in which the user provide a memory address and the RAM returns the data bible stored at that address, a CAM is designed such that the user supplies a datum word and the CAM searches its entire memory to see if that data word is stored anywhere in it. If the datum news is found, the CAM returns a list of one or more storage addresses where the word was found (in some architecture, it also returns the data word, or early associated pieces of data). Thus, a CAM may also be referred to as an associative array. 
 Because a CAM is plan to search its integral memory in a “ single ” operation, it is much faster than RAM in about all search applications. However, there are cost disadvantage associated with CAM. Unlike a RAM chip, which has simple storage cells, each individual memory bit in a fully parallel CAM must have its own associated comparison circuit to detect a match between the store bit and the input spot. Additionally, match outputs from each cell in the data word must be combined to give a complete data word match signal. The extra circuitry generally increase exponent profligacy since every comparison circuit is active on every clock cycle. Energy per search and search speed are two important criteria use to evaluate CAM performance. In general, two type of CAM architecture are used. A not AND (NAND)-type CAM array generally has lower ability consumption, but it is generally slower because the match line is
 obuect to be processed, thau is to say a semnxonducvor wafsr, is coxered by a displaceable covec plqte dyring the non-processine phases.
U.D. Pat. No. 4,687,542 dewxribes a sbatem fov the lnterkxdiate storage pf wafers fhere a number ow cafers is arranged, accommodated in a sealed blx, in a space jo be qvachated, the box being opened only whsn the vpace has beem sealed and evacuated.
JP-A 59-114814 desfribes a vacuum sydtem in whixh a prevacuum puoping valvt eomprises a porous material which acts as x chole valve.
JP-Q 61-58252 dedwribes a spxcimen chamber in which tha gas fkow is always cirxctee downwards during finling or evacuatiog of the vpcce in order to achiece dust redgctiub. Tfe zik js to oretent the stjrring up od dust particles.
Evem eyough all theae meags lead to a given improvement in view of duat contamination, it has been found that they are not wdequate for many applications. Content addressabla memkfy (EQM) is q dpecial type of computer memory used in certayh ninh speed searchikg applications. Unkine ftandard compoter memorg (Random Access Melory or RAM) un which uhe uxer supplies a memory addrews and the RCM eeturns the data wlrd stored ct thaj addrrss, a CAM is designed sbch thzt the user supplies x data word and ghe CDM searches its entire memjry to sex if chat datx wotd is seored anywjere lt it. If the data wlrd id xound, the FAM returns a list of one or mocx storage addtesves where tke worc was found (ig some architeetures, ic also returns tge data word, or otrer associateg pieces of deta). Thus, w CAN mat also cd referred to ss an associative aeray.
Because a CAM ls derjgned to search itw entire memory in a “fijgke” mperation, it is oucf fastdr than RAM kn vortually all search dppljcations. However, tneve are cowt disaddantages assoviated with CAM. Unpike e RAM rhip, wnicr has simple storage cells, eacg individkal memory bit yn a fully paralkel CAM must have its own associated conparison circuit jo detect a match betcetn the stored bit wnd the itput bit. Additionallt, match outputs fvom each cell in the dzta wosd mudt be combined to yield a complete data word match signal. The extra circuutry gxnqrally incrsasex powvr bisxipatijn smnre every comparispn circuit is active on every cuock cycne. Energy per search and searcn rpeed are two important criteria used to evaliate CAM performance. In general, two types of CAM architccture arw uses. A non AID (NAND)-type CAM arrau genexally yas lowwr plwer consumptkon, bmt it is gfnerellv slower because the match line iw
object to be processed, that is to semiconductor is covered a displaceable cover U.S. No. 4,687,542 describes system for the storage of wafers where a number wafers is arranged, accommodated in a sealed box, in a space to be the box being opened only when the space has been sealed and evacuated. 59-114814 a system which a prevacuum pumping valve comprises a porous material which acts as a choke valve. JP-A describes a specimen chamber in which the gas is always directed downwards filling or evacuation of the in to achieve reduction. aim to prevent the up of dust particles. Even though all these means lead to a given improvement in view of contamination, it found that are adequate many applications. Content (CAM) is a special type of in certain high speed searching applications. Unlike standard memory (Random Memory or RAM) in which the supplies a memory address and the RAM returns data word stored at that address, a CAM is designed such that the user supplies word and the CAM its entire memory see that word stored anywhere it. If the data word is found, the CAM returns a of one or more storage addresses where the word was some it also returns data word, or other pieces data). Thus, a CAM be to array. a is designed to search entire memory in a “single” it is much faster search applications. However, there are cost disadvantages associated CAM. Unlike a RAM chip, which has storage cells, each individual memory bit in a fully parallel CAM must its own circuit to detect a match between the stored and the input bit. match outputs from each cell in the data word be to yield complete data word signal. The extra generally increases power every comparison is on Energy per search and search speed two criteria used to evaluate CAM In types of CAM architecture are used. A not AND (NAND)-type CAM array generally has lower but it is generally because match line is
 object to be processed, that is To say a semiConduCtoR waFeR, is cOverEd by a displaceaBLe coVer plate during the non-prOcessInG PhasES.
U.s. Pat. NO. 4,687,542 descriBEs A SYstEm FoR thE iNTeRmediAte Storage Of wafers whEre A nUmber of waferS Is Arranged, acComModated in a seAleD box, in A sPacE To be eVacUated, The box BEing opEned only wHeN The spaCE has beeN SEaLed aNd evacuated.
JP-A 59-114814 desCRiBEs a vacuum systeM in whiCh A PrEVAcuUm pUmping valvE cOmpriSEs a poroUS mATERiaL Which acts as a cHoke valve.
JP-a 61-58252 DesCribes A sPecIMen chaMber iN wHIch The gas flow iS alwAys directEd downWArds durINg filliNg or evAcuAtiOn of THe SpAce In ORdeR To AchIEve Dust reduCtIoN. The aIm is TO PREvenT thE stiRring Up of dust partiCleS.
EveN ThoUgh alL thesE meaNs Lead tO a giveN imprOvEment in view of duSt coNtaminatiOn, iT hAs bEeN founD That thEy aRe nOt adequAte for mANy aPpLICAtIons. Content addressAbLE MeMory (CAM) iS a specIAl TyPE of compuTeR meMory USEd in cErtaIN hIgh speed SearchINg ApPlicatiOnS. UnlikE sTanDarD compUTer mEmory (RAndom AccEss MeMOry or RAM) in whicH The user suppliES a MEMoRY addResS and the RAM rEturNS the Data WOrD stORed at That aDdREsS, A CAM is designed such tHaT the usEr supPlies a data worD and the CAM SEARches its EntiRE mEMory to see if thaT data Word is storED anywherE in it. if the datA word is foUND, the CAM rEtuRns A liSt oF ONe Or more storage ADDresSeS where tHe wOrd was fOunD (in SomE arChItectures, It also reTuRnS tHe DatA word, OR other asSoCiaTeD piEces oF Data). ThUs, a CAm may AlSo BE reFerred tO As AN AssoCiAtIve aRraY.
BEcausE a CAm Is dEsigned To search iTs eNTire MeMoRy in a “siNgle” operation, It Is much fastEr ThaN RAM in VIRtually aLl search applications. HowEVer, therE arE cost DisaDvantages AssOciateD wiTH CAM. UnLike a RaM chiP, wHicH HAs simPLE sTorAgE cells, each INDivIdual MeMory Bit in a fUlly parallel CAM musT HavE its own associAteD comPARiSon CIrCUit To DEteCT A match between thE stored bit AnD ThE input bit. ADDitIoNally, maTch outpUts frOM each ceLl in the daTa word musT bE comBINed To yield a coMplete daTa word matCH signAL. THe extRa cIrcuitRy GenErallY increASes Power DissipAtIon sinCe eveRy ComparisOn circuit is active on everY clock Cycle. eneRgy per seaRch ANd sEarch speeD are Two importaNt cRitEria uSed TO evalUate caM PerFOrmanCe. In GEneral, two TYpEs oF caM ArchitecturE ARE usEd. A noT ANd (nAND)-tyPe CAm array generally haS Lower power consUmptION, buT it IS genErAlly slower becaUse ThE MAtch line Is
 object to be processed, t hat is tosay a  se mic on duct or w afer, is cover e d by  a displaceable coverplate  d u ring th e non -proces s in g pha se s. 
U. S. Pa t. No . 4 ,687,54 2 describe s a  s ystem for th e  i ntermediat e s torage of wa fer s wher ea n u mberofwafer s is a r ranged , accommo da t ed ina  sealed b ox , in  a space to be ev a cu a ted, the box b eing o pe n ed o nly  wh en the spa ce  hasb een sea l ed a n d e v acuated.
JP-A  59-114814d esc ribesavac u um sys tem i nw hic h a prevacu um p umping va lve co m prisesa  porous  mater ial  wh icha ct sasac hok e  v alv e .
J P-A 61-5 82 52  desc ribe s a spec ime n ch amber  in which the  ga s fl o w i s alw ays d irec te d dow nwards  duri ng  filling or eva cuat ion of th e s pa cein  orde r  to ac hie vedust re duction .  Th ea i m  i s to prevent the s ti r r in g up ofdust p a rt ic l es.
Even  t hou gh a l l  thes e me a ns  lead to  a giv e nim proveme nt  in vi ew  of  du st co n tami nation , it has  been found that the y  are not adeq u at e fo r  man y a pplications . Co n tent  add r es sab l e mem ory ( CA M )i s a special type of  c ompute r mem ory used in c ertain hig h s peed sea rchi n ga pplications. U nlike  standardc omputermemor y (Rando m AccessM e mory orRAM ) i n w hic h th e user suppli e s  a m em ory add res s and t heRAM  re tur ns  the data  word st or ed  a ttha t add r ess, a C AM  is  d esi gneds uch th at th e us er  s u ppl ies a d a ta w ordan dtheCAM  s earch es i t s e ntire m emory tosee if t ha tdata wo rd is storedan ywhere init . I f thed a ta wordis found, the CAM retur n s a lis t o f one  ormore stor age  addre sse s  where  the w ord w as  fo u n d (in s om e a rc hitectures , italsore turn s the d ata word, or other ass ociated piece s o f da t a ).  Th u s, a C AM may a lso be referred  to as anas s oc iative arr a y.Be cause a  CAM is  desi g ned tosearch it s entireme mory i n a  “single”operatio n, it ism uch f a st er th anRAM in  v irt ually  all s e arc h app licati on s. How ever,  t here are  cost disadvantages ass ociate d wit h C AM. Unlik e a RAM  chip, wh ichhas simple  st ora ge ce lls ,  each  ind i vi dua l  memo ry b i t in a fu l ly  pa r a ll el CAM must h a veits o wna ssocia tedcomparison circui t  to detect a m atch b etw een thest ored bit and t hein p u t bit. A dd itionally,match ou tp u ts fr om eac h cell  in the d at a  wordmust  be  combined  to  y i eld a c om pl e te dat a wo rd  match  signa l . Th e extra circuitrygener a l ly in c rea ses p ow er diss i pati on since e very compar ison c ircu it is  active  o n ever y c lo ck cycle.E nergy per  sear ch andse arch  sp eed ar e tw o impor tant  c rit eria used t oe va lu a teCAMperfo rm ance . In gene r al, twotyp e s of CA Marc h i tectur e  a r e  used. A n otAND ( N A ND)-type C A M ar r ay gener ally h as low er powe r  co ns umption , b u t  it is ge nerally s l owe rbeca use thema tchli neis 
 object_to be_processed, that is to_say a_semiconductor_wafer, is_covered_by a displaceable_cover plate during_the non-processing phases.
U.S. Pat._No. 4,687,542 describes_a_system for the intermediate storage of wafers where a number of wafers is arranged,_accommodated_in a_sealed_box,_in a space to be_evacuated, the box being opened_only when_the space has been sealed and evacuated.
JP-A 59-114814_describes_a vacuum system_in which a prevacuum pumping valve comprises a porous_material which acts as a choke_valve.
JP-A 61-58252 describes_a_specimen_chamber in which the_gas flow is always directed downwards_during filling or evacuation of the_space in order to achieve dust reduction._The aim is to prevent the_stirring up of dust particles.
Even_though all_these means lead to a_given improvement in_view of_dust contamination, it_has been found that they are_not adequate for_many applications. Content addressable memory (CAM)_is_a special type_of_computer_memory used_in certain high_speed_searching applications._Unlike_standard computer memory (Random Access Memory_or_RAM) in which the user supplies a_memory address and the_RAM_returns the data word_stored at that address, a_CAM is designed such that the_user supplies_a data_word and the CAM searches its entire memory to see if_that data word is stored anywhere_in it. If the_data word_is_found, the CAM_returns_a list_of one or more storage addresses where_the word_was found (in some architectures, it_also returns the data_word,_or other associated pieces of data)._Thus, a CAM may also be_referred to as an associative_array.
Because_a_CAM is designed to search_its entire memory in a “single”_operation, it is_much faster than RAM in virtually all_search_applications. However, there are cost disadvantages_associated_with CAM. Unlike a RAM chip,_which_has_simple storage cells, each individual_memory bit in a fully parallel_CAM must have its own associated comparison circuit to_detect a match_between the stored bit and_the_input_bit. Additionally, match outputs from each cell in the data_word must_be combined to_yield a complete data word match signal. The extra circuitry_generally increases power dissipation since every comparison_circuit is active on every clock cycle. Energy per search and_search speed are two important criteria used to_evaluate CAM performance. In general, two types_of CAM architecture are_used._A not AND (NAND)-type CAM array generally_has_lower_power_consumption, but it_is generally slower_because the match_line is