1Imprint-based Fabrication and ApplicationsZhaoning Yu, Ph.D.Advanced StudiesHP LabsPalo Alto, CA 94304Email: [email protected] 235/NSE 203: Nano-scale FabricationUniversity of California – Berkeley Mar.14, 2007Outline Imprint-based fabrication for nano-gratings Scatterometry: Real-time Imprint Monitoring (RIMS) Frequency Doubling for ultra-high density nano-wire arraysPart1: Imprint-based fabrication techniques Nanofluidic channels for biological applications Subwavelength optical elementsPart 2: Applications of nano-scale gratings2Outline Imprint-based fabrication for nano-gratings Scatterometry: Real-time Imprint Monitoring (RIMS) Frequency Doubling for ultra-high density nano-wire arraysPart1: Imprint-based fabrication techniques Nanofluidic channels for biological applications Subwavelength optical elementsPart 2: Applications of nano-scale gratingsBackground: gratings by mechanical rulingdiamond ruling toolAl (or Au)mirrordetectorslowgrating carriagediamond carriage Not good for gratings with very fine pitches ( < 1µm ): Total length of grooves is limited by diamond wear Mechanical stability: < 12 strokes/min Slow: days to weeks3Grating pattern generation by interference lithographysubstratek1k2θθθλsin2=Λ Grating period: λ of light source: 351.1 nm0 102030405060708090012345θ (degree)Λ⁄λ200 nmλ= 351.1 nmInterference lithography set-upFor generating periodic patterns over large areabeam-splittervariableattenuatormirror mirrorsubstratelenspinholepinholelensθθlaser beamλ = 351 nmphotoresist4I(x,t) D(x)∫TdttxI0),(Contrast degradation caused by system instability∫=TdttxIxD0),()(mMmMDDDDD+−=γDose profile:Contrast in D(x): Noise and instability degrade image contrastInterference lithography: exposure results200 nmresistARCSiO2Si substrate500 nmresistARCSiO21-µm period200-nm period Contrast is much lower for reduced grating period52D array by interference lithography1 µmresistSiO2SiO2resistARC200 nm 1- µm period: easy 200 nm period: very difficultInterference lithography: pattern transfer steps1. Exposure & development2. Shadow Cr3. Shadow Cr4. Three-step RIECrCrARCsubstratephotoresistSiO2CrLift-offRIE‘dry’ development‘wet’ development Tri-layer resist scheme6Effect of dry development on pattern contrast200 nmresistARCSiO2Si substrate200 nmresistARCSiO2Si substrateAfter exposure & developmentAfter shadow evaporation & O2 RIE Wafers up to 4-in. can be patterned Remaining problems: Line-edge roughness Line-width controlInterference lithography: remaining problems200 nmresistARCSiO2Si substrateResist grating by interference lithography Sidewall roughness Line-width control* M. Farhoud, et al., J. Vac. Sci. Technol. B 17(6), 3182 (1999).period = 200 nm7Steps of Nanoimprint Lithography (NIL)substratemoldresist1. Press in mold2. Heat up mold and substrate3. Separation after cooling4. O2RIE1. Resist grating by NIL2. RIE to isolate lines3. Thermal annealingNIL resistsubstrateRoughness reduction technique by thermal re-flow200 nm200 nmZhaoning Yu, L. Chen, W. Wu, H. Ge, and S. Y. Chou, J. Vac. Sci. Technol. B 21, 2089 (2003)8Roughness reduction using wet-etched Si mold1. SiO2grating in (111) direction2. Anisotropic etching of Si3. Remove SiO2mask SiO2(110)(111)(110) Si substrateNIL MoldSiO2Si200 nm200 nmZhaoning Yu, L. Chen, W. Wu, H. Ge, and S. Y. Chou, J. Vac. Sci. Technol. B 21, 2089 (2003)200 nm period smooth-edged grating in resist after NIL200 nm200 nmTop view Cross-section Duplicated pattern in resist9(KOH:DI:IPA)-based wet-etch of SiL2L1X2(KOH)X2(H2O)X2(IPA)X1(KOH)X1(H1O)X1(IPA)beakertemperature probestir barhot plate4-inch waferExperimental set-up2-phase mixtureKOH:DI:IPA=500g:1600ml:400mlSi etch-rate characterization test structuresWtWodWbR111R110R111mask(110) SiαdWtWoWbR111mask(100) SiR100R111(100) Si substrate (110) Si substrate10Wet-etched (110) Si test structure(a)200 nm(110) substrate(110)(111)(b)200 nm(110)(111)(110) substrate (110) substrate: vertical sidewallsWet-etched (100) Si test structureSiO2(100) substrate(b)200 nm(111)(100) substrateSiO2(a)200 nm(100) substrate (100) substrate: triangular profile11Etch-rate dependence on temperature55 60 65 70 75 80 85 9050100150200250300350R110R110 (nm/min)T (°C)R11055 60 65 70 75 80 85 900102030405060R111R111 (nm/min)T (°C)R111 65°C for better control and uniformityFabrication of triangular profile grating mold(100) Simask(111) plane1. Pattern SiO2grating 2. KOH:DI:IPA wet-etch 3. Remove mask200 nmmask(111)Zhaoning Yu and Stephen Y. Chou, Nano Letters 4, 341 (2004)12Grating fabrication using the triangular-profile moldCr6. O2RIE 7. CHF3RIE 8. Cleaning5. Shadow CrmoldresistSiO2Si1. Spin resist 2. Imprint 3. SeparationCr4. Shadow CrmoldRoughness reduction through wet-etch and NIL(100) Si(111) planeSiO2SiO2IL patterned grating mold duplicated gratingmold Roughness reduction resulting from wet-etch13Reduction in grating line edge roughness200 nm(a)SiO2Si substrate200 nm(b)SiO2Si substrateinterference lithography triangular mold NIL NIL: improved line-edge smoothnessGrating line-width control in the triangle mold processθwΛα°=74.54αCr maskimprinted resist θαtantan112+Λ=w Grating line-width:200 nm200 nm200 nm200 nm14Improvement in line-width control compared to IL * M. Farhoud, et al., J. Vac. Sci. Technol. B 17(6), 3182 (1999).interference lithography *Nonlineartriangular mold NILLinearperiod = 200 nm period = 200 nm Different line-widths can be easily achievedImprovement in line-width uniformity Same width after shadow and RIEwide SiO2 linesmoldnarrow SiO2 linesmoldImprint & shadow O2RIEIL & wet-etchCrCrCrresistresist15Mold separation process smaller contact area ( ~ 65% of a square mold ) no “friction” problemTriangular Mold:triangular moldhresistsquare moldh“friction”-FFresistFabrication of 2D structures by NIL1. Spin resist2. Imprint second grating3. Pattern transfer 4. 2D moldresist substrate with grating200 nm200 nm162D structures by NIL: pattern transfer ImprintO2RIELift-offCHF3RIE1.2.3.4.moldresistsubstrateCrCr200 nm200 nmOvercoming the λ-limit: frequency-doublingSiO2SiSi3N4Si Mold1. 200 nm period2. CVD Si3N43. RIE4. Remove SiO25. 100 nm pitch100 nmTop view100 nmCross-sectionZhaoning Yu, W. Wu, L. Chen, and S. Y. Chou, J. Vac. Sci. Technol. B 19, 2816
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