光刻技术及应用.docx

光刻技术及应用.docx

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光刻技术及应用

Lithography

Lithography（fromGreekλ?

?

θο?

?

lithos,"stone"+γρ?

?

φειν,graphein,"towrite"）isamethodofprintingoriginallybasedontheprinciplethatoilandwaterdonotmix.[1]Printingisfromastone（lithographiclimestone）orametalplatewithasmoothsurface.Itwasinventedin1796byGermanauthorandactorAloisSenefelderasacheapmethodofpublishingtheatricalworks.[2][3]Lithographycanbeusedtoprinttextorartworkontopaperorothersuitablematerial.[4]

Lithographyoriginallyusedanimagedrawnwithoil,fat,orwaxontothesurfaceofasmooth,levellithographiclimestoneplate.Thestonewastreatedwithamixtureofacidandgumarabic,etchingtheportionsofthestonewhichwerenotprotectedbythegrease-basedimage.Whenthestonewassubsequentlymoistened,theseetchedareasretainedwater;anoil-basedinkcouldthenbeappliedandwouldberepelledbythewater,stickingonlytotheoriginaldrawing.Theinkwouldfinallybetransferredtoablankpapersheet,producingaprintedpage.Thistraditionaltechniqueisstillusedinsomefineartprintmakingapplications.

Inmodernlithography,theimageismadeofapolymercoatingappliedtoaflexiblealuminumplate.Theimagecanbeprinteddirectlyfromtheplate（theorientationoftheimageisreversed）,oritcanbeoffset,bytransferringtheimageontoaflexiblesheet（rubber）forprintingandpublication.

Asaprintingtechnology,lithographyisdifferentfromintaglioprinting（gravure）,whereinaplateiseitherengraved,etched,orstippledtoscorecavitiestocontaintheprintingink;andwoodblockprinting,andletterpressprinting,whereininkisappliedtotheraisedsurfacesoflettersorimages.Today,mosttypesofhigh-volumebooksandmagazines,especiallywhenillustratedincolour,areprintedwithoffsetlithography,whichhasbecomethemostcommonformofprintingtechnologysincethe1960s.Thewordlithographyalsodenotesphotolithography,amicrofabricationtechniqueusedinthemicroelectronicsindustrytomakeintegratedcircuitsandmicroelectromechanicalsystems.

Theprincipleoflithography

Lithographyusessimplechemicalprocessestocreateanimage.Forinstance,thepositivepartofanimageisawater-repelling（"hydrophobic"）substance,whilethenegativeimagewouldbewater-retaining（"hydrophilic"）.Thus,whentheplateisintroducedtoacompatibleprintinginkandwatermixture,theinkwilladheretothepositiveimageandthewaterwillcleanthenegativeimage.Thisallowsaflatprintplatetobeused,enablingmuchlongerandmoredetailedprintrunsthantheolderphysicalmethodsofprinting（e.g.,intaglioprinting,letterpressprinting）.

LithographywasinventedbyAloisSenefelderinBohemiain1796.Intheearlydaysoflithography,asmoothpieceoflimestonewasused（hencethename"lithography":

"lithos"（λιθο?

?

）istheancientGreekwordforstone）.Aftertheoil-basedimagewasputonthesurface,asolutionofgumarabicinwaterwasapplied,thegumstickingonlytothenon-oilysurface.Duringprinting,wateradheredtothegumarabicsurfacesandavoidedtheoilyparts,whiletheoilyinkusedforprintingdidtheopposite.

Lithographyonlimestone

LithographystoneandmirrorimageprintofamapofMunich

Lithographyworksbecauseofthemutualrepulsionofoilandwater.Theimageisdrawnonthesurfaceoftheprintplatewithafatoroil-basedmedium（hydrophobic）suchasawaxcrayon,whichmaybepigmentedtomakethedrawingvisible.Awiderangeofoil-basedmediaisavailable,butthedurabilityoftheimageonthestonedependsonthelipidcontentofthematerialbeingused,anditsabilitytowithstandwaterandacid.Afterthedrawingoftheimage,anaqueoussolutionofgumarabic,weaklyacidifiedwithnitricacidHNO3isappliedtothestone.Thefunctionofthissolutionistocreateahydrophiliclayerofcalciumnitratesalt,Ca（NO3）2,andgumarabiconallnon-imagesurfaces.Thegumsolutionpenetratesintotheporesofthestone,completelysurroundingtheoriginalimagewithahydrophiliclayerthatwillnotaccepttheprintingink.Usinglithographicturpentine,theprinterthenremovesanyexcessofthegreasydrawingmaterial,butahydrophobicmolecularfilmofitremainstightlybondedtothesurfaceofthestone,rejectingthegumarabicandwater,butreadytoaccepttheoilyink.[5]

Whenprinting,thestoneiskeptwetwithwater.Naturallythewaterisattractedtothelayerofgumandsaltcreatedbytheacidwash.Printinginkbasedondryingoilssuchaslinseedoilandvarnishloadedwithpigmentisthenrolledoverthesurface.Thewaterrepelsthegreasyinkbutthehydrophobicareasleftbytheoriginaldrawingmaterialacceptit.Whenthehydrophobicimageisloadedwithink,thestoneandpaperarerunthroughapresswhichappliesevenpressureoverthesurface,transferringtheinktothepaperandoffthestone.

Senefelderhadexperimentedduringtheearly19thcenturywithmulticolorlithography;inhis1819book,hepredictedthattheprocesswouldeventuallybeperfectedandusedtoreproducepaintings.[2]Multi-colorprintingwasintroducedbyanewprocessdevelopedbyGodefroyEngelmann（France）in1837knownaschromolithography.[2]Aseparatestonewasusedforeachcolor,andaprintwentthroughthepressseparatelyforeachstone.Themainchallengewastokeeptheimagesaligned（inregister）.Thismethodlentitselftoimagesconsistingoflargeareasofflatcolor,andresultedinthecharacteristicposterdesignsofthisperiod.

"Lithography,orprintingfromsoftstone,largelytooktheplaceofengravingintheproductionofEnglishcommercialmapsafterabout1852.Itwasaquick,cheapprocessandhadbeenusedtoprintBritisharmymapsduringthePeninsulaWar.Mostofthecommercialmapsofthesecondhalfofthe19thcenturywerelithographedandunattractive,thoughaccurateenough."[6]

Themodernlithographicprocess

A1902lithographmap（originalsize33×24cm）

High-volumelithographyisusedpresentlytoproduceposters,maps,books,newspapers,andpackaging—justaboutanysmooth,mass-produceditemwithprintandgraphicsonit.Mostbooks,indeedalltypesofhigh-volumetext,arenowprintedusingoffsetlithography.

Foroffsetlithography,whichdependsonphotographicprocesses,flexiblealuminum,polyester,mylarorpaperprintingplatesareusedinsteadofstonetablets.Modernprintingplateshaveabrushedorroughenedtextureandarecoveredwithaphotosensitiveemulsion.Aphotographicnegativeofthedesiredimageisplacedincontactwiththeemulsionandtheplateisexposedtoultravioletlight.Afterdevelopment,theemulsionshowsareverseofthenegativeimage,whichisthusaduplicateoftheoriginal（positive）image.TheimageontheplateemulsioncanalsobecreatedbydirectlaserimaginginaCTP（Computer-To-Plate）deviceknownasaplatesetter.Thepositiveimageistheemulsionthatremainsafterimaging.Non-imageportionsoftheemulsionhavetraditionallybeenremovedbyachemicalprocess,thoughinrecenttimesplateshavecomeavailablewhichdonotrequiresuchprocessing.

LithographypressforprintingmapsinMunich

Theplateisaffixedtoacylinderonaprintingpress.Dampeningrollersapplywater,whichcoverstheblankportionsoftheplatebutisrepelledbytheemulsionoftheimagearea.Hydrophobicink,whichisrepelledbythewaterandonlyadherestotheemulsionoftheimagearea,isthenappliedbytheinkingrollers.

Ifthisimageweretransferreddirectlytopaper,itwouldcreateamirror-typeimageandthepaperwouldbecometoowet.Instead,theplaterollsagainstacylindercoveredwitharubberblanket,whichsqueezesawaythewater,picksuptheinkandtransfersittothepaperwithuniformpressure.Thepaperpassesbetweentheblanketcylinderandacounter-pressureorimpressioncylinderandtheimageistransferredtothepaper.Becausetheimageisfirsttransferred,oroffsettotherubberblanketcylinder,thisreproductionmethodisknownasoffsetlithographyoroffsetprinting.[7]

Manyinnovationsandtechnicalrefinementshavebeenmadeinprintingprocessesandpressesovertheyears,includingthedevelopmentofpresseswithmultipleunits（eachcontainingoneprintingplate）thatcanprintmulti-colorimagesinonepassonbothsidesofthesheet,andpressesthataccommodatecontinuousrolls（webs）ofpaper,knownaswebpresses.AnotherinnovationwasthecontinuousdampeningsystemfirstintroducedbyDahlgreninsteadoftheoldmethodwhichisstillusedonolderpresses（conventionaldampening）,whicharerollerscoveredwithmolleton（cloth）whichabsorbsthewater.Thisincreasedcontrolofthewaterflowtotheplateandallowedforbetterinkandwaterbalance.Currentdampeningsystemsincludea"deltaeffectorvario"whichslowstherollerincontactwiththeplate,thuscreatingasweepingmovementovertheinkimagetocleanimpuritiesknownas"hickies".

ArchiveoflithographicstonesinMunich

Theprocessoflithographyprintingisseenhere.[8]Thissimplifiedversionofalithographicprintingpressgivesyouanideaofhowtheprintingprocessworks.Thispressisalsocalledaninkpyramidduetothefactthattheinkistransferredthroughseverallayersofrollerswithdifferentpurposes.Thelithographicprintingpressesarecommonlyusedinnewspaperproductionwherefastrollingandjumpingrollsareafamouspartofthepressingsceneineverynewspaperproductionmovie.

Theadventofdesktoppublishingmadeitpossiblefortypeandimagestobemodifiedeasilyonpersonalcomputersforeventualprintingbydesktoporcommercialpresses.Thedevelopmentofdigitalimagesettersenabledprintshopstoproducenegativesforp