Lecture 16 Chemical Engineering for Micro/Nano Fabrication Next: 193nm Lithography
Absorption coefficient [1/µm] Absorption of Photoresist Polymers 2.8 Poly-(4-hydroxystyrene) 2.4 Meta-cresol novolak 2.0 ArF 193 nm KrF 248 nm i-line 365 nm 1.6 1.2 0.8 0.4 Polyacrylates (aliphatic) 0.0 175 200 225 250 275 300 325 350 375 400 Wavelength [nm] Source: R.D. Allen et al., IBM J. Res. Develop. 41 (1/2), 95-104 (1997)
Impact of Photoresist Absorbance on Developed Image Profile Exposure Step Final Profile Moderate absorbance High absorbance
Relative Etch Rate Relative Etch Rate of Polymers Aliphatic Aromatic Carbon
The hnishi Number Watanabe, F. and hnishi, Y., J. Vac. Soc. Technol. B,422 (1986)
193 nm Resist Materials Challenge: 248 and 365 nm resists are unsuitable for 193 nm imaging because they are opaque at this wavelenth Etch resistance requires high carbon/hydrogen ratio but aromatics are precluded because of their absorption How do you achieve both 193nm optical transparency and etch resistance?
High C:H Ratio of Alicyclic Hydrocarbons The key! Structure: CH 3 (CH 2 ) n CH 3 Formula: C 6 H 6 C 12 H 16 C 7 H 10 C n H 2n+2 Unsaturation Number: 4 5 3 0
APEX 248nm Resist Design CH CH 2 CH CH 2 tbc H Tethering Function Acid Lability Base Solubility Etch Resistance
UTexas193nm Design [ ] [ ] C C(CH 3 ) 3 C H Tethering Function Acid Lability Etch Resistance Base Solubility
Early Lithography Resist 0.80 0.20 C C + Ø 3 SSbF 6 H C(CH 3 ) 3 poly(nbca-co-cbn) Synthesis requires metal catalyst! Excellent image quality Adhesion failure
Trading Etch Resistance for Adhesion: Alternating Systems: CMA + V601 THF 70C x H 3 C CCH 3 CH 3 V601 N N CCH 3 CH 3 CH 3 Waco Chemical No Metal! Yield : M n : M w : Pd : 60% 4,660 6,860 1.472 Shelf Life issues?
Images in UT 193nm CMA Resist Alternating co-polymer Uzo koroanyanwu, Jeff Byers
Improving Etch Resistance + V601 Dioxane 70C x DNBC UV Absorbance 0.44 mm -1 @ 193 nm Yield : M n : M w : Pd : 55 % 3,400 4,340 1.276 With JSR
Performance Resist and Process Development Basic Chemistry Formulation and Process Development 248nm ptimization I-line 193nm Issues! Time
Fujitsu s Acrylic Platform CH 2 H C C m CH 2 H C C n CH 2 H C C o CH 2 H C p C H Acrylate Copolymers Free radical polymerizations No metal
Acrylic Polymer Platform H F 3 C CF 3 H F 3 C CF 3 Fujitsu IBM,JSR, etc. H CF 3 CF 3
Types of PAGs Used For 193 nm Lithography R R TPS S + R DPI INIC I + VLATILE F 3 C S 3 - S 3 - NN-INIC N S Ar SIT ALS S + R NN-VLATILE AsF 6 - Rf S 3 - N S CF 3 MDT NEALS NAT. Tf CH 3 CH 3 S + S + F 3 C PF 6 - CF 2 CF 2 CF 2 S 3 - nonaflate : too weak for 193 nm S 3 - H S N S CF 3 MBT NIT
193nm Resist Challenges Pattern Collapse Line Edge Roughness (LER) Etch Resistance Heisenberg Principle issue Pattern Collapse New Defect Types m Bridging LER
Line edge Roughness 193 248
Simulation of a PE Bake Blocked sites Unreacted polymer Latent Image Edge Gerard Schmid
Influence of Base on LER Base quencher can decrease the acid sphere of influence in low contrast regions, thereby reducing LER. I(x) Acid Base x No base With base J. E. Meiring, T. B. Michaelson, G. M. Schmid and C. G. Willson, Proc. SPIE, 5753(2005), to be published
Exploring Base Effects To add base quencher seems to make the contrast higher, thereby LER reducing. I(x) x x x 0% base 15% base 30% base 6.61 nm RMS 5.47 nm RMS 3.89 nm RMS J. E. Meiring, T. B. Michaelson, G. M. Schmid and C. G. Willson, Proc. SPIE, 5753(2005), to be published
Typical ArF KrF system always shows dramatic moderate variation of DR dissolution dissolution rate(a/sec) 100000 Comparison of ArF and KrF 10000 1000 100 10 1 0.1 Low contrast value Gradually increasing DR No DR @ Unexposed area 0< DR @ Unexposed area 0.01 1.0 10.0 100.0 No DR changes until this point DSE(mJ/cm2) Moderate Rmax Uniform DR inside film Quite high Rmax Different DR inside film Suddenly the dissolution begins The contrast is very high total total surface surface middle middle bottom bottom
DR Dissolution behavior KrF System H ArF System This difference in the contrast amplifies small variations in the blend region. Digital n/ff switching phenomenon makes the line edge rough.
DR Is there such a thing as too much contrast? The KrF system has lower contrast Small fluctiuations cause small changes in dissolution rate.. The ArF system changes from insoluble to soluble over a very narrow dose range Small fluctuations are amplified and cause huge changes in dissolution rate. Stochastic process noise becomes line edge roughness
Could have been Can it be done again at 157nm??? Perhaps.but This time it would have been really hard!!
Absorption (mm -1 ) of Common Polymers Transmission 0.00001%!!! Wavelength (nm) 157.6 193 248 248 resist 6.84 0.37 193 resist 6.86 0.47 Polystyrene* 6.20 Polynorbornene* 6.10 PMMA* 5.69 Fluorocarbon* 0.70 * R.R.Kunz,et al., Proc. SPIE 3678, 13 (1999). Vacuum UV 2, H 2 absorbs at this wavelength Even hydrocarbons like butane and polyethylene absorb strongly
Fluorination of Norbornane Skeleton F F paque n F F n Transparent? F? 248 nm 193 nm 157 nm How many fluorines and where to fluorinate?
Selective Fluorination of Norbornane F Absorbance (mtorr -1 cm -1 ) F F F F F 150 155 160 165 170 175 180 Wavelength (nm) Geminal substitution at the two carbon bridge is the most effective fluorination pattern -CF 3 acrylates
Surprising Serendipitous Discovery Ni (II) H + CF 3 CF 3 n n CF 3 CF 3 F 3 C F 3 C H A 157 = 2.57 mm -1 A 157 = 1.15 mm -1 NBHFABC and NBHFA are surprisingly transparent T. Chiba, et. al., J. Photopolym. Sci. Technol, 13 (2000) 657-664
Absorbance of Fluorinated Polymers CH 3 Absorbance (mm -1 ) 7 6 5 4 3 2 (6.02 mm -1 ) CH 2 C CMe (5.42 mm -1 ) CF 3 CH 2 C CMe CF 3 CF 3 (2.68 mm -1 ) (2.44 mm -1 ) 1 0 150 160 170 180 190 200 Wavelength (nm) CF 3 CF 3 (1.15 mm -1 ) Hexafluoroisopropyl and -trifluoromethylcarboxylic acid are groups surprisingly transparent! H
Some Imaging Results 100nm 90nm 80nm 60nm 40nm
Performance Resist and Process Development Basic Chemistry 60nm Formulation and Process Development 248nm ptimization I-line 157 nm 193nm We are well off the base line Time
Images in UT 157nm Resists 70nm Intel Announcement Issues include: Pace, Resist, Pellicles, CaF 2, Birefringence, Cost, etc. 85nm 60nm 34