High Refractive Index Polymer Platforms for 193nm Immersion Lithography

Transcription

1 High Refractive Index Polymer Platforms for 193nm Immersion Lithography Ratnam Sooriyakumaran Daniel P. Sanders Hoa Truong Robert D. Allen IBM Almaden Research Center Matthew E. Colburn Gregory R. McIntyre IBM Albany NanoTech

2 High Index Polymer Platforms utline Introduction Need for high index resist Some guidelines for material selection Screening for high index polymer platforms Sulfur based compounds Aromatic systems Silicon back-bone polymers Summary: Screening of Materials Polycarbosilane polymer design and challenges High Index resist development and performance Nanocomposite Resists Conclusions 2

3 Will a high index resist offer improved imaging performance? Loss of contrast at high NA (> 1) due to TM polarization component can be reduced by increasing the refractive index (RI) of the resist Brunner et. al., Proc. SPIE, 4691 (2002) Improvement in Exposure Latitude and MEEF are predicted for resists with RI > 1.8 using unpolarized illumination at high NA; RI ~ 2.0 has the greatest benefit Conley et. al., 3 rd International Symposium on Immersion Lithography Also potentially valuable for high index immersion lithography with NA > 1.6 3

4 Possible Approaches Many high RI elements not compatible with resist requirements Alkali metals, alkaline earth metals, transition metals, main-group metals, and halogens (except fluorine) prohibited from photoresists. Possible approaches: Aromatic and heteroaromatic compounds (w/ manipulation of abs. bands) Group VIA (S, Se) compounds Phosphorous compounds Group IVA (Si, Ge ) compounds 4

5 Relationship between Refractive Index and Absorbance Kramers-Kronig Relationship Anomalous dispersion Normal dispersion n n - Refractive Index k Extinction Coefficient k λ kmax λ nmax Wavelength [nm] Both n & k increase as the wavelength approaches an absorption peak (nd) However, n reaches its maximum (λ nmax ) just before k reaches its max. (λ kmax ) (ad) If λ nmax ~ 193 nm, one would have a material with high index and relatively low abs. Look for materials that have λ kmax closer to but blue shifted from 193nm 5

6 Screening for High Index Materials So far we have screened more than 100 candidate materials including: Sulfur Compounds Aromatic compounds Silicon compounds n & k values were measured at SEMATECH Absorbance verified by UV spectra 6

7 Previous Work on Sulfur Compounds Andrew Whittaker et. al., U. Queensland Proc. SPIE, 6519, , (2007) x S y S S S Yukio Nishimura et. al., JSR Corp. 3rd Intl. Symposium on Immersion Lithography wt% S needed to get n = 1.85 Best resist: n = 1.76, Abs = 1.70 μm -1 ~ 7.7 wt% S 80 nm imaging n = 1.76 n = 1.80 Abs = 5.22 μm -1 Abs = 7.20 μm 148 nm nm 90 nm Current issues Higher percentage of sulfur needed to achieve n > 1.8 High absorbance associated with high sulfur content Poor lithographic performance when sulfur content is high 7

8 We feel sulfur-containing resists offer limited potential Almaden materials screen x x x x S S S S n = 1.69 Abs = μm -1 n = 1.75 n = 1.82 n = 1.86 Abs = 1.51 μm -1 Abs = 3.29 μm -1 Abs = 5.28 μm -1 D increases more than n with increase in sulfur content Decreased resist sensitivity Poor image profiles High sulfur content could cause etch and outgassing problems 8

9 E o Increases with Increase in Sulfur Content ( ( ) ) S CF 3 CF 3 H FARM: NBHFA/ECPMA NBHFA/ECPMA 60:40 NBHFA/ECPMA/ETCPMA 55:40:05 NBHFA/ECPMA/ETCPMA 50:40:10 NBHFA/ECPMA/ETCPMA 45:40:20 ETCPMA E o (mj/cm 2 ) at 123 o C PEB

10 Tuning aromatic compounds had limited success Fluorination blueshifts absorption band, increases n, decreases k x n 193 = n 193 = k 193 = k 193 = α 10 = μm -1 α 10 = μm -1 F x n F n k k Still too absorbing! F F Wavelength [nm] Wavelength [nm] Useful lessons, but materials unlikely to be useful for this application 10

11 Another Approach: Silicon Back-Bone Polymers Polymer Refractive Index (n) at 193-nm Absorbance (α 10 /μm) At 193-nm Poly(Cyclohexylmethylsilane) ( Si ) n Polycarbomethylsilane Aldrich, Mw ~ ( Si CH 2 ) n Polycarbomethylsilane Aldrich, Mw ~ 3500 H Silicon Content 48 wt.% ( Si CH 2 ) n H Poly(dimethylsilylethylene) ( Si CH 2 CH 2 ) n Carbosilane polymers have higher refractive index and relatively low absorption at 193-nm 11

12 Summary: Screening of Materials Sulfur containing resists offer limited potential Higher absorption at 193 nm Poor litho performance May have etch and outgassing problems Tuning aromatic compounds had limited success Even when substituted with strong electron withdrawing groups, absorption is too high Carbosilane polymers offer better optical properties than any yet reported Unsubstituted polycarbomethylsilane has n = 1.96, Abs. = 3.6 / μm Very high silicon content enables it to be used in thin film imaging schemes Next: Functional Carbosilane Polymers 12

13 Carbosilane Polymers: Starting Materials ( Si CH 2 ) n H Polycarbomethylsilane (PCMS) Aldrich Chemical Company: Solid materials, Hyperbranched, possibly have Si-Si linkages Narrow polydispersity Mw = 1229, Mn = 798, PDI = 1.54 Possibly Yajima polycarbosilane (S. Yajima et al., Nature, 1976, 260, 683) Starfire Systems (NY) Liquid, May be linear, Very broad polydispersity Mw = 5500, Mn = 874, PDI =

14 Functional Carbosilane Polymers Functionalyzed by Hydrosilation Reaction R H Si CH 2 R Si CH 2 R x Hydrosilation Catalyst It was possible to substitute only about 50% of the available Si-H in Aldrich Polymers In Starfire System polymers, it was possible to substitute more than 90% of the Si-H; Polydispersity > 5, the polymer becomes insoluble in most organic solvents Most of our work was carried out with Aldrich polycarbomethylsilane (PCMS) Difunctional monomers were used to increase the amount of useful functional groups R x 14

15 Carbosilane Polymers: GPC Data 30 Aldrich PCMS After Hydrosilation 15 MV 15 MV Minutes Minutes Mw = 1229, PDI = 1.54 Mw = 5682, PDI = Starfire PCMS After Hydrosilation 8 MV 6 MV Minutes Mw = 5500, PDI = Minutes Mw = , PDI =

16 Designing Functional Carbosilane Polymers Difunctional monomers are needed for dissolution 220 PCMS-VAA ( ) ( ) Si CH 2 Si CH 2 a b H Film Thickness (nm) H Dissolution Rate by QCM Time in 0.26 N TMAH (sec) PCMS-2Almalomi (RS ) ( ) ( ) Si CH 2 Si CH 2 a b H Film Thickness (nm) H H Time in 0.26 N TMAH (sec) 16

17 Functional Carbosilane Polymers: Examples n & k Measured at SEMATECH ( ) ( ) Si CH 2 Si CH 2 a b PCMS Source Aldrich R - functional group (after hydrosilation) MCP ester-nb n 1.83 A (α 10 )/μm 2.62 H Aldrich PCMS Substitution < 50% Narrow PDI Soluble in most organic solvents Starfire PCMS Substitution > 50% Broad PDI Solubility in organic solvents very low R Aldrich Aldrich Aldrich Aldrich Starfire Starfire AllylHFA NB methanol Allylmalonic acid 2-Allylphenol MCP ester-nb/ NBDCAH Vinylacetic acid Protected with Angelicalactone

18 193nm Litho Performance Contrast curves High Index Resist PCMS-ALMTHP (RS ) PEB = 40-89C (PAB=110C, ptiyield/60s) CH Si H Si CH2 CH 2 CH 2 CH 2 Thickness(Å) T40C T43C T46C T49C T52C T63C T67C T75C T83C T89C R R 1 10 Dose(mJ/cm 2 ) R = THP Polymer n = 1.83 Abs = 1.99 μm -1 TPSN Formulation n = 1.82; Abs = 2.60 μm -1 Low absorbing PAGs may help 170 nm l/s, 159 nm thick film, PEB 60 0 C/60, 23.2 mj/cm2 0.6 NA ISI ministepper 18

19 Litho Performance Needs Improvement CH2 Si H Si CH2 CH 2 CH 2 CH 2 Resist n = 1.81 Abs = 2.43 μm -1 R R R = Angelicalactone 193 nm ISI mini-stepper (0.6NA), CG PAB/PEB = 110C/70C/60s, on AR nm 1:1 140 nm 1:1 150 nm 1:1 FT=113 nm Residue may be due to mismatch with the ARC 160 nm 1:1

20 Nanocomposite Resists with High Index Nanoparticles Photoresists containing silicon dioxide nanoparticles have previously been reported Fedynyshyn et. al., Proc. SPIE, 3999, 627 (2000) Conceivably, high index resists could be formulated with nanoparticles with high index We recently received Material A from Prof. Emmanuel Giannelis at Cornell Sufficiently dispersed in chloroform only We were able to cast clear films of Material A: n = 2.01; k = 0.098; Abs = 2.78 μm-1 20

21 Material A: Thin Films Relatively high absorbance at 193nm UV Spectrum (Film Thickness: ~ 0.19 μm) 0.995@182nm 1.0 Absorbance (AU) @193nm Abs. : 2.46 / μm Wavelength (nm) This level of absorption may be acceptable in thin film resist applications However, we were unable to disperse Material A in photoresists due to limited solubility in most organic solvents 21

22 Summary and future work Achieving n of with D < 2.5 μm -1 is possible with carbosilane polymers (current resists: n ~ 1.7) Carbosilane resists can be used in thin film imaging schemes Low Absorbing PAGs and bases may help limit the absorption of the resist Better carbosilane starting materials are needed to synthesize functional polymers with improved properties and resist performance High Index nanoparticles may offer additional boost to index; Need to be functionalized to improve solubility in resist solvents We may be able to achieve n ~ 1.9 by combining carbosilane polymers with nanoparticles; However, synthetic and formulation challenges remain It may be very difficult to develop a resist with n > 1.9; But, the greatest benefit in process improvement is predicted when n ~ 2 22

23 Acknowledgements SEMATECH Georgia Rich and Alvina Williams for n&k measurements Prof. Emmanuel Giannelis of Cornell for providing Material A Paul Zimmerman for useful discussions 23