Journal of Photopolymer Science and Technology Volume 20, Number 5 (2007) 637-642 @TAPJ Oxime Sulfonate Chemistry for Advanced Microlithography Hitoshi Yamato, Toshikage Asakura, Yuichi Nishimae, Akira Matsumoto, Junichi Tanabe, Jean-Luc Birbaum, Peter Murer, Tobias Hintermann and Masaki Ohwa Technology Center Electronic Materials, Coating Effects Segment, Ciba Specialty Chemicals K.K., 7-1-13, Doi-cho, Amagasaki, Japan 660-0083 Oxime sulfonate compounds are one of the important chemistry as photoacid generator for advanced lithography application and practically used in mass production of semiconductor chips. This chemistry is adjustable for various applications like g-/h-/i-line, KrF and ArF lithography. This paper describes an overview of oxime sulfonate chemistry for semiconductor resist application, including commercially available products. Keywords: oxime sulfonate, photoacid generator, g-line, i-line, KrF, ArF, chemically amplified resist 1. Introduction The development of semiconductor chips is desired resist performance such as resolution, making progress with an astonishing speed, depth-of-focus, line edge roughness and etching enabling electronic apparatus smaller, higher resistance, the acid-labile polymers have been speed, and higher performance. This dynamic intensively studied first and developed notably. For advancement is significantly attributable from the further improvement of the CA resist, PAG is the development of photolithography technology. At key ingredient. Several chemistries have been an early era of integrated circuits (IC) extensively investigated as the photoactive manufacturing lithography technique was component for the CA resists, e.g., iodonium introduced with light source of g-line wavelength sulfonate, sulfonium sulfonate, (436 nm). For further miniaturization of IC the diazomethanedisulfone, N-sulfonyloxyimido wavelength of light source is getting shorter and compounds, nitrobenzyl sulfonate, and so on [3]. shorter, i.e., i-line (365 nm), KrF (248 nm) and Among them, we have particularly paid attention ArF (193 nm). Currently ArF immersion is actively to oxime sulfonate chemistry due to its potential investigated as the most advanced technology, and ability as latent acid and its wide structure EUV (13.5 nm) is discussed as the next generation variation. lithography. When the g-line and i-line light We have developed several oxime sulfonate sources were used, the resist comprised compounds, aiming to g-/h-/i-line, KrF and ArF diazonaphthoquinone (DNQ) as photo-sensitive lithography. In addition, a sensitization of oxime component [1]. However, after introduction of KrF sulfonate has been investigated. These studies are laser, the DNQ resist can’t be employed for the described in this paper. advanced lithography because the absorption of DNQ resist at 248 nm and 193 nm is too high to 2. PAG for g-/h-/i-line application transmit the light throughout the resist to the Recently there are demands for broadband and i-line bottom. As an alternative technology, chemically resist with high sensitivity, high resolution and thick amplified (CA) resist was developed [2]. The CA thickness. DNQ resist has been widely used for resist is composed of polymer bearing acid-labile broadband and i-line applications so far but its groups and photoacid generator (PAG). Photolytic decomposition of PAG during light exposure performance does not satisfy such new demands generates acids in the CA resist. This acid acts as and the CA resist is attracted for these applications. catalyst to facilitate de-protection reaction of ester Chloromethyl triazines with extended conjugation group or acetal group of polymer, rendering are known as suitable PAG for g-/h-/i-line exposure polymer matrix alkaline-soluble. For achieving 637 Received April 6, 2007 Accepted May 21, 2007 J・P肋叩OJy〝7・Scf・乃C加oJ・，VbJ・20，No・5，2007 ［41．However hydrochloric acid photochemically retainsagoodsolubilityabove15％inPGMEAas generated from chloromethyl triazineis highly SurrlmarizedinTable2．TbegoodsolubilityofPAG volatile and corrosive and can be a concem minimizestherisk of particle generation dunng regarding potentialdamage ofthe manufactunng resiststorageandimprovesformulationflexibility． equlPment．Since sulfonic acids areless volatile， less mobileandless corrosive，they aretherefore Preferred over hydrochloric acidin the resist ab le 2 S olu b ility in P G M E A applications．Thoughonly afew sulfonic acid iC U P A G lX X Solubility （％） generators sensitive up to g－line arekn0wn・We 10 3 20 havebeeninvestigatingoximesulfonatetypePAG． 108 ＞30 This chemistry can be a4iusted to the target 12 1 17 applicationsand exposure wavelengthrange by Selectionfromawiderangeofchromophoresand acidmoieties． 2．4 Bemeretalreportedoximesulfonateaslatent 1．9 acidcatalystforcoatingapplicationl5］butsuch qJ COmPOunds do not have absorpt10ninalonger 宣1．4 月 WaVelength．Aiming for gr瓜－／i－1ine 叩Plication， L O t′l IRGACURE㊨pAGlXXseriesisnewlydeveloped 毒0・9 l6］・Figurel shows UV absorption．spectrum， 0．4 indicatlngSu伍cientlyred－ShiftedabsorptlOnPrOfile －0．1 OVerg－line（436nm）withtheLmaxat405nm．Ths 200 300 400 500 600 red－Shiftedprofileisattributablefromtheextended WaYek口車hくnm） COqugatedsystembycombinationofphenylnng Figure2tTVabsorptioTLChangeolICtlPAGlXX 肌dqulnOidestruCtureOfthiophenerlng．Withour upOneXpOSure negative tone modelformulationIRGACURE㊨ PAGlXXshowsagoodsensitivitynotonlywithi－ 1ineexposurebutalsowithg－1ineexposure． Figure2displaysachangeofUVal）SOrPtlOnin acetonitrile solution upon exposure to436mm monochromaticlight．A distinctive absorption at TabIclIRGACURE⑧pAGlⅡ 255nmemergedandtheabsorptlOnabove420mm ICUPAG lXX Acidgene叫ed COmpletely disappeared during exposure・The 103 n－Propanesulfomicacid qu血m yield ofphotolysi岳，Od，WaS determined 108 nJCktanesulfomicacid fromtheabsorptlOndecreaseat436nm，indicatlng 121 p－Toluenesulbnicacid thatofIRGACURE⑧pAG103wasO．13．Similarly theamountofacidgenerated upon exposurewas determinedbytheindicatordyemethod．InFigure 3，thedec托aSeOfthenormalizedal）SOrPt10nat 3已d七〇的qく 【ひくdp名望己＼【p竃pOl已苫払】 L O． 0．2 00 4 L O． 0．2 00 4 0hO洪d巴08pONdd∈JON 弓－票寸－d喜や巳OS焉 190 240 290 340 390 440 490 Wavelength／nm FigurelUVabsorptionofICtJPAGlO3 0 100 200 300 400 Exposuretime（min） As7t－COIt）ugation ofanOrganic moleculeis extended，the solubilityofthe molecule usually Figure3AcidgenerationandtJVchangeofICtl becomeslower．HoweverIRGACURE⑧pAGIXX PAGlXXuponexposure 638 J・P加opo抄肌Scf・乃C九oJ・，VbJ・20，No・5，2007 436 mm and the normalized molar acid qompnslng POlyhydroxystyrene（PHS）based concentration（relative to initial molar PAG polymer and PAG was developed for KrF concentration）ofthe photochemically generated lithography・There are mainly two polymer ● acid were plotted agalnst eXPOSure time・It was PlatformSWithdi飽rentacid－hbilegroups・Oneof foundthatthe decrease ofabsorptlOn at436mm themis so－Called acetaltype polymer，i・e・，PHS （photobleaching）was equaltothegeneratedacid Partiallyprotectedwithacetalgroup・Tもeotheris concentration when both were normalized tothe so－CalledESCAPtypepolymer，i・e・，CO－POlymerOf initialmolarPAGconcentration．Thissuggeststhat PHS andtert－butylmethacrylate．The acetaltype phot0－decompositionofIRGACURE㊨PAGIXX POlymerCanbede－PrOteCtedbelow1100Catpost－ quantitatively generates acid・Tberefore，the exposure baking（PEB），Whilethe ESCAP type quantum yield of photolysis，4＞d，COrreSPOnds POlymerneedstobeheatedintherangeof120－ directlytothatforacidformation，¢a，thus 1300C． IRGACURE⑧pAGIXXisthermallystableup la／¢d＝l to1550Cinthe neatformbut the stal）ilitylS loweredto1400CinapolymermatriX．ThisPAGis The reportedla／．d ratiosfor oxime sulfonates StableenoughfortheapplicationofacetaltypeKrF werefoundintherangeofO．6toO．8［7］．Hence，it resist．On the other hand，thereis ariskinits was concluded thatIRGACURE㊨ pAGIXX applicationforESCAPtypeformulationintermsof PrOvides good or superior photoacid generation thermaldecompositionofPAGatPEB・ e鍋ciency，basedongoodacidconversionyield・ Wehavestudiedthethermalstabilityofoxime TもestorageStabilityofPAGisoneofcritical SulfonateanddevelopedthermallystableKrFPAG， requlrementSfor CA resist application・Because IRGACURE㊨ pAG 203［8］．Ths 00mpOund ev飢Smal1amOuntOfacidcanCauSedegradationof possessestrifluoromethylgroupa句acenttooxime CAresist．ThestabilityofIRGACURE㊥pAGIXX group， Which stabilizes this molecule・ areevaluatedbymonitorlngaCidconcentrationin IRGACURE㊥pAG203isstableupto1880Ceven thesamplestoredatvarioustemperatureatfrequent inapolymermatriXandover2000Cinaneatform intervals．No acidformation was observed after asshowninFigure5．Tberefore，thisPAGcanbe morethanlyearstorageevenat400C．Whenthe employedin both acetal and ESCAP type sampleisstoredat40C，IRGACURE⑧pAGIXX formulations． hasfoundtobestablemorethan5years，弧dthe evaluationisstillcontinued． びくd⊃望POPgd＼写0鴫PO盲やuOヱ（竺【gl00806 040200 lrgacurePA6203 0 50 100 150 200 250 300 Th℃（W由り J ‾ l ■● ■◆● ■′ ’．■ ■．t ■ Figure4Storage stability ofICtJPAG103in t ●● neatmrm き〇一－霊石工 l l 3．PAGfbrKrFapplication When KrF excimer－laser（248 nm）yas introducesasthelightsourceforresistapplicatlOn， 「■● ● －■ ● theconventionalDNQresistcouldnotbeemployed Temp（C） duetoahighabsorptlOnOfnovolakpolymermatriX and DNQ molecules．Tberefore，the CA resist Figure5DSCcurvesofICtJPAG203 639 J・P加opoJym・Scf・mc〝OJ・，VoJ・20，Nb・5，2007 As can be seen 丘om the UV absorptlOn methyladamantylmethacrylate）is a key reaction spectruminFigure6，IRGACURE⑧pAG203has dunngthelithographyprocess・Tもeoximesulfonate anabsorptlOnValleyaround248mmandshowsa COmPOunds with a stropg acid such as relativelylowabsorptionatthewavelengthofKrF Perfluoroalkylsulfonate have been