Screening of basic resist materials and PAGs for EUV-Lithography 1. Int. EUVL-Symposium, Dallas, TX Klaus Lowack, Wolf-Dieter Domke, liver Kirch, Karl Kragler, Heinz-Ulrich Scheunemann* Infineon Technologies AG, 915 Erlangen, Germany * BESSY GmbH, 12489 Berlin, Germany Never stop thinking. eturn to Listing
Introduction: EUV absorbance The EUV absorbance in organic materials is done by inner-shell electrons and is therefor - differently from optical lithography - independent of molecular structure. The attenuation length plot defines the depth, where the EUV radiation is attenuated to 1/e of the initial energy [LBNL CX]. Attenuation lengths at 13.4 nm wavelength ( 94 ev) are converted to EUV absorbance using Beers law. EUV absorbance goes proportional with the heteroatom/carbon ratio I-line, DUV and 193nm resists all show more or less the same EUV absorbance of 3-6 µm -1 The fluorine content in 157nm resist result in a higher EUV absorbance of 5-1 µm -1 Siloxane and CH-units in the polymer lower the EUV absorbance EUV absorbance [1/µm] 2 18 Teflon 16 14 12 1 157 8 PI PC 6 PMMA *) Heteroatom are 4 193 non-c 2 and non-h 248 PP 365 Siloxan,,5 1, 1,5 2, 2,5 Heteroatom *) /Carbon atio
Absorption of various Polymers and PAGs EUV absorbance [1/µm] 7 6 5 4 3 2 1 TPS-Nonaflate DPI-Triflate bis-tbutyl-pi- Nonaflate TPS-Hexaflate bis-tbutyl-pi- Hexaflate bis-tbutyl-pi-triflate TPS-Triflate *) Heteroatom are non-c and non-h, 1, 2, 3, 4, 5, 6, Carbon/Heteroatom *) atio bis-tbutyl-pi-tosylate The strongest absorbing atoms in resists and PAGs are J > F > >> N > C, Cl, S, H Triphenylsulfonium PAGs have a lower absorbance than Diphenyliodonium PAGs longer CF 2 chains in the PAG anion increase the absorbance (nonaflate > hexaflate > triflate) While for the polymer it is advantageous to have a low absorbance, this is not yet proven for the PAGs
Materials under Investigation: Polymers & PAGs Acrylic MA type I, Si-containing PSS-type Acrylic-MA-polymers were prepared by radical polymerization. Si(CH 3 ) 3 CH 3 X CH 3 Y PSS-type polymers and PAG materials were used as received. PHST and ESCAP type materials were used as reference. Acrylic MA type II Si Si Si Si Si Si Si Si = i-bu C H PHST type The photoacid generators used were Triphenylsulfonium- (TPS), Diphenyliodonium- (DPJ) and bistbutylphenyliodonium (tb-dpj)salts of trifluorosulfonic- (Triflate), hexafluorosulfonic- (Hexaflate) and nonafluorosulfonic (Nonaflate) acid. Ph 3 S + CF 3 S 3 - Ph 2 J + (tbu-ph) 2 J + CF 3 CHF CF 2 S 3 - CF 3 (CF 2 ) 3 S 3 - H C ESCAP type
EUV Beamline at the Berliner Elektronenspeicherring- Gesellschaft für Synchrotronstrahlung (BESSY) Main parts of the BESSY EUV setup: Pre-mirror is a low-pass for the absorption of high energetic photons to prevent multilayer-mirror damage Multilayer-mirror for in-band EUV (12.5-13.5 nm) Si-membrane window (option) for vacuum separation and contamination protection Exposure chamber with dose control
Exposure Chamber Details at BESSY Spectral Power [mw/nm] 7,E-1 6,E-1 5,E-1 4,E-1 3,E-1 2,E-1 1,E-1,E+ Spectral Intensity at the EUV-Beamline Dipol Spectrum Spectrum after Pre-mirror Spectrum after 2 Multilayer-mirrors 5 1 15 2 25 3 35 4 wavelength [nm] Spectral Power [mw/nm] 1,E-1 8,E-2 6,E-2 4,E-2 2,E-2 Spectral Power Distribution at EUV-Beamline,E+ 12 12,5 13 13,5 14 14,5 15 wavelength [nm] without Si-Window after.5 µm Si 11 µw/cm² 45 µw/cm² pen Frame area : 3 mm x 6 mm Intensity: 12 µw/cm 2 at 2 ma ring current Uniformity: +/- 2,5 % over a range of 42 mm; +/- 1,25 % over a range of 38 mm dose calibration: with AXUV-1 diodes (PTB) with a sensitivity of,254 A/W dose increments are achieved with a rotating chopper wheel using either linearly or logarithmic spaced openings other parameters: 1-6 mbar pressure,exposure times sec - min
What can we learn from bulk lithographic EUV data? Film thickness [nm] 12 1 8 6 4 2 Though lithographers are mainly interested in small pattern and pattern profiles, a lot of information can be gained from open frame maesurements: - resist sensitivity and contrast, - unexposed film thickness loss, - resist loss at.75 E - negative tone behavior at higher doses Data at different bake temperatures can be used to extract parameters for resist simulation. The resist image can also be used to characterize the exposure uniformity of the beamline setup and allow easy control of changes in this setup..1 1. 1. Dosis [mj/cm2] Exposure dose: 1.3 mj/cm 2 Y Axis [mm] 5 1 15 2 25 3 Filmthickness [nm] 12 1 8 6 4 2,1 1, 1, EUV Dose [mj/cm 2 ] High sensitivity, high contrast 1 2 3 4 5 6 X Axis [mm] Medium sensitivity, medium contrast 11. -- 12. 1. -- 11. 9. -- 1. 8. -- 9. 7. -- 8. 6. -- 7. 5. -- 6. 4. -- 5. 3. -- 4. 2. -- 3. 1. -- 2. Step width: 2mm Height scale: nm Dose Uniformity of BESSY exposure field (3 x 6 mm) from filmthickness measurements of developed resist
esults & Discussion I Acrylic MA type II resist with TPS X-flates PAG showed, that the variation of the PAG anion chain length (increasing F- content, increasing absorbance in EUV) has a significant impact on sensitivity in EUV compared to DUV. The shortest anion gave best sensitivity and contrast. Film Thickness [nm] 12 1 8 6 4 2 Nonaflate Hexaflate Triflate 8 7 6 5 4 3 2 1 2,5 2 1,5 contrast Nonaflate Hexaflate Triflate Dose-to-clear [mj/cm 2 ] γ DUV γ EUV D DUV D EUV,1 1 1 1 dose-to-clear [mj/cm 2 ] 3, 2,8 2,6 2,4 2,2 2, 1,8 1,6 1,4 1,2 1,,8,6,4,2, dose [mj/cm 2 ] dose-to-clear vs. F-content in resist,2,3,4,5,6,7,8,5 Nonaflate Hexaflate Triflate The dose-to-clear increases linearly with the molar fluorine content of the resist F-content in resist formulation [mmol]
esults and Discussion II Film Thickness [nm] 12 1 8 6 4 2 Acrylic MA type II resist with S- or J-containing cations show a higher sensitivity and a better contrast with the higher EUV absorbing J in the cation. This is also true for the PSS polymers: the J- containing resist is 4-5 times faster in EUV than in DUV. The PSS polymers show all high contrast. PSS Polymer, 5 % PAG 3,5 3 2,5 2 1,5 1,5 TPS Hexaflate DBuPJ Hexaflate Dose-to-clear [mj/cm 2 ] D DUV Film Thickness [nm] 12 1 8 6 4 2 D EUV 12 1 8 6 4 2 TPS Hexaflate DBuPJ Hexaflate Acrylic MA polymer, 5% PAG γ DUV contrast γ EUV TPS Hexaflate DBuPJ Hexaflate DPJ Triflate 1 1 dose [mj/cm 2 ],1 1 1 dose [mj/cm 2 ]
esults and Discussion III Acrylic MA type II resists gives systems with high sensitivity and no netative-tone behavior up to a dose of 25 mj/cm2, which is a Eneg/E ratio of > 3. ne of the reference systems (ESCAP) showed a negative tone behavior at 4 times E. PAG type and photobase can be used to adjust the sensitivity (A: TPS Triflate; B TPS nonaflate + TPS acetate). The acrylic copolymer itself is patternable at doses of 3 mj/cm 2. GPC & I data suggest main chain scissioning. 2 C) without PAG GPC: Film Thickness [nm] 12 1 8 6 4 2 A) with PAG B) with PAG & base C B A Mw [1 3 g/mole] 1 9 8 7 6 5 4 3 1 2 3 4 5 6 tboc group molecular weight vs. EUV dose EUV dose [mj/cm 2 ],1 1 1 1 dose [mj/cm 2 ] Exposure without PAG (sample C) gives TMAH-developable material without any changes in the content of deblocking groups. FT-I of Sample C after EUV exposure at 6 mj/cm 2
esults and Discussion IV 12 acrylic MA type I; 23 % tbu; 5% TPS Hft, base acrylic MA type II; 45 % tbu, 5% TPS Hft, no base FT-I spectrum (type I) before EUV exposure: Film Thickness [nm] 1 8 6 4 2,1 1 1 CH 3 CH 2 C= (SA) C-- CH 2 CH 3 tbu C= (Ester) --tbu dose [mj/cm 2 ] With PAG containing resist, the main mechanismus is the deblocking, however, the polymer itself undergoes also main chain scissioning. t-boc content and base addition give similar effects as known from DUV... with exposure decreases.. FT-I difference spectrum: changes with EUV exposure CH 3 C= (Ester) Bandshift C-- CH 3 tbu --tbu FT-I microscopy is a valid method for the investigation of structure changes with dose. increases.. -CH C= (SA) C= (Acid)
Summary & Acknowledgement An EUV beamline has been built at the BESSY GmbH for open frame characterization of basic resist materials and PAGs. A set of polymers with F-, S- and J-containing PAGs has been investigated for their bulk lithographic behavior at 13.4 nm exposure wavelengths. The sensitivities of these resists range from.8 to 11 mj/cm 2, contrast values range from 3 to 14. The EUV absorbance of the PAG anion & cation has an important impact on sensitivity. ecommendations for good combinations of anions and cations could be given. The acrylic MA resist showed no negative tone behavior up to 3 times their dose-to-clear. All acrylic co-polymer resist systems will undergo partial main chain scissioning during EUV exposure. preliminary patterning tests of the acrylic MA type I and II polymers at the EUV-LLC 1x microstepper show the potential for high resolution and moderate LE. The work at BESSY will continue with some emphasis on outgassing and on extraction of resist model parameters. Acrylic MA type I resist: Sensitivity 7.4 mj/cm 2 resolution 8 nm overall LE: 5.2 nm Acrylic MA type II resist: 4 nm lines We thank Ingrid Wiechert for the open frame exposures at BESSY and Donna Connell for the patterning at the EUV-LLC. National funding for the BMBF project 1 M 364A is gratefully acknowledged