The use of Modified Polytetrafluoroethylene for 157nm and 193nm Soft Pellicles Paul A. Zimmerman, Chris van Peski, and Danny Miller International SEMATECH Andrew Proctor Intel Corporation Ryan P. Callahan and Matthew Cashion University of Texas, Austin
Outline Introduction (old work) Approach Materials Transparency Experimental Details Irradiation Chamber, Starting Materials, and Exp. Conditions, results Moving forward (new work) Approaches Results Conclusions
Introduction: Goals and Approach Develop a polymer that can meet requirements for 157nm pellicle Incorporate learning's from University projects Focus on systems that have reasonable economics < $400.00/pellicle Material should be useful for 193 and 248nm lithography Develop first from a robustness standpoint and then seek to improve transparency
Transparency Polymer systems need cross-linking, rings, heteroatoms, or branching to break up σ-conjugation (Source French et al. DuPont) Introducing hydrogen to improve transparency causes rapid degradation of all material in which it is used Systems can easily be designed and synthesized that meet the >70% initial transparency goal; however, all fail to survive or stabilize at useful transparencies The most transparent (and longest lived) species at 157nm are the perfluoropolyethers
Proposed New Materials CF CF CF 2 CF CF CF 2 CF CF 2 CF CF 2 CF 2 CF CF CF 2 CF CF 2 CF CF CF 2 CF CF 2 CF CF CF CF CF 2 CF 2 CF CF CF 2 CF 2 CF CF 2 CF CF CF 2 CF CF 2 CF CF 2 CF CF CF 2 CF CF 2 CF CF CF C CF 2 CF O CF CF 2 O CF 2 CF 2 O CF 2 CF O CF CF O CF O CF 2 CF O CF CF 2 O CF CF 2 CF O CF 2 CF O CF 2 CF O CF 2 CF CF CF CF 2 O CF CF CF O CF CF O CF 2 CF O CF 2 CF CF CF 2 O CF CF CF CF 2 CF CF 2 CF CF CF O CF 2 CF O CF 2 CF CF 2 CF 2 O CF CF 2 O CF 2
Absorption Spectrum of PTFE Absorption Intensity Intensity 5 6 7 8 9 10 11 ev
Experimental: Irradiation Chamber Cu Gasket Al Frames Heater Cavities Thermocouple Ports SS Cap Ti Foil SS Plate Al Chamber Conflat Fitting for Valve Assembly
Experimental: Materials and Conditions Used PTFE (~6.5µm), FEP (~13µm), and PFA (~13µm) (Commercial Grade) Materials were held at T m during irradiation Irradiation conditions: 5mA @800kV with 5 sec sweeps of the e-beam on the material Stacked free standing films in Ar atmosphere Fluorination of the films carried out in the same chamber (20% F 2 in N n ) E.R Lovejoy, M.I. Bro, and G.H. Bowers, Chemistry of Radiation Crosslinking of Branched Fluorocarbon Resins. J. Appl. Polymer Sci., 9, 411, (1965). A. Oshima, S. Ikeda, E. Katoh, Y. Tabata, Chemical structure and physical properties of radiation-induced crosslinking of polytetrafluoroethylene, Rad. Physics and Chem., 62, 39, (2001). U. Lappan, U Geissler, L. Häussler, D. Jehnichen, G. Pompe, K. Lunkwitz, Radation-induced branching and crosslinking of poly(tetrafluoroethylene) (PTFE), Nucl. Inst. and Methods in Physics Res. B 185, (2001)
Irradiation of PTFE Films Red = Control PTFE Light Green = Irradiated (~3.5MGy/cm 2 ) % Transmission Dark Green = Irradiated (~7MGy/cm 2 ) 100 Blue = Irradiated (~7 MGy) and F 2 treatment 90 80 70 60 50 40 30 20 10 0 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 Wavelength (nm)
XRD Data of PTFE and Irradiated PTFE Control PTFE Irradiated PTFE
Comparison of PTFE, FEP, PFA % Transmission 100 90 80 70 60 50 40 30 20 10 0 Blue = PTFE Green = FEP Red = PFA 120.6 140.6 160.6 180.6 200.6 220.6 240.6 260.6 280.6 300.6 Wavelength (nm)
Modified PTFE at 193nm and 248nm Paul Zimmerman Modified Extruded PTFE UV-VIS Spectra Tested at 193nm 400 Hz 100 Transmission (%) 95 90 85 80 PZ F-PTFE Baseline PZ F-PTFE 756 J/cm2 Dose PZ F-PTFE 3.7 KJ/cm2 Dose 75 70 185 190 195 200 205 210 215 220 225 230 235 240 245 250 255 Wavelenght (nm) Wavelength (nm)
TOF-SIMS Data pre and post-exposure 4 x10 1.4 C 3 F Red = Irradiated + F 2 Blue = Irradiated and exposed 1.2 1.0 C 4 H 7 C 3 H 8 N Intensity 0.8 C 4 H 9 0.6 0.4 C 4 H 5 C 3 H 4 N C 3 H 6 N 0.2 52 54 56 58 / u
TOF-SIMS Data (Cont) 3 x10 C 3 F 3.5 3.0 Red = Irradiated + F 2 Blue = Irradiated and exposed 2.5 C 4 H 7 Intensity 2.0 1.5 1.0 0.5 55.0 / u
TOF-SIMS Data (Cont. d) Intensity 2 x10 6.0 5.0 4.0 3.0 2.0 1.0 C 13 F 25 Control PTFE Intensity 2 x10 7.0 6.0 5.0 4.0 3.0 2.0 1.0 C 13 F 25 Irradiated PTFE Intensity 2 x10 6.0 5.0 4.0 3.0 2.0 1.0 C 13 F 25 Irradiated and Exposed PTFE 700 800 900 1000 / u
Crosslinking Density of Irradiated Films Assume the yield of Crosslinks for the films = G(X) = 3 Dose: 1MGy = 100 MRad The number of events per 100 units = G(X) * MW(g/mol) * Dose (MRad) *1.036 x 10-6 *100% = 3*50*100* 1.036 x 10-6 *100 = 1.55 CF 2 units per 100 involved in crosslinks Therefore at a dose of 7MGy there will be a crosslink every 100/1.55/7 ~ 9.2 units Source: Principles of Radiation Chemistry, O Donnell and Sangster, p. 166
Most Recent work Approaches Modify material in hand Reduce thickness of 6.5 µm thick PTFE to 1 µm Increase cross linking density to improve transparency Tried to obtain 2 µm thick PTFE from several companies No response to requests Exploration of new materials
Results: Exposure Dose Variation PTFE (e-beam and F2 treated) Transmission % 100 90 80 70 60 50 40 30 20 10 0 5 min (3.4 MGy/cm2) 10 Min (6.8 MGy/cm2) 15 Min (10.2 MGy/cm2) 20 Min (13.6 MGy/cm2) 120 140 160 180 200 220 240 260 280 300 wavelength(nm)
XPS Results CF x CF 2 CF 2 C CF 2 CF 2
Conclusions New Approach of increasing dose to reduce thickness and improve transparency does not work It is likely that 2µm PTFE will be suitable for the process and produce extremely transparent and resilient membranes New materials may also offer options, however, this can t be said with certainty
Acknowledgements Sematech- Georgia Rich,Vicki Graffenberg, The Whittaker Group (University of Queensland), Roger Sinta MIT/LL, The Turro Group (Columbia University), The Yue Kuo Group (Texas A&M), The Desmarteau Group (Clemson), The Chuminov and Luzinov Groups (Clemson) St. Gobain for providing a significant amount of the starting materials for the project Disclaimer: SEMATECH, the SEMATECH logo, International SEMATECH, and the International SEMATECH logo are the registered servicemarks of SEMATECH INC. ARMC, ATDF, the ATDF logo, Advanced Technology Development Facility, ISMI and the International SEMATECH Manufacturing Initiative are servicemarks of SEMATECH INC. All other service marks and trademarks are the property of their respective owners.