Thin Resist film Processing issues Ioannis Raptis Patterning

Thin Resist film Processing issues Ioannis Raptis Patterning Group Institute of Microelectronics National Center for Scientific Reasearch ‘Demokritos’ 15310 Ag. Paraskevi Attikis, Greece E-mail: raptis@imel. demokritos. gr http: //imel. demokritos. gr Contents ØGlass transition changes in thin resist films ØEtching rate of thin resist films ØDissolution properties of thin resist films 1

SW-OPTI methodology / Results Operation Principle Interference Equation Parameters affecting Tgfilm qfilm thickness qfilm – substrate interactions qcoating method qdistribution of molecules At glass transition v. Specific volume v. Refractive index v. Surface roughness change Exposure layout 50 m rectangular pads C. D. Diakoumakos, I. Raptis Polymer 44 251(2003) D. Niakoula, I. Raptis, D. Goustouridis, P. Argitis Jpn. J. Appl. Phys. 43 (5247)2004

Tgfilm values of AZ-EM materials MMC 13: terpolymer Mw: 30000 MMC 14: terpolymer Mw: 14000 MMC 15: terpolymer Mw: 45000

MW-OPTI interferometry method / Results Specifications: Real time calculation of polymeric film thickness Controlled heating and cooling rate Controlled atmosphere (humidity level) Results: Evaluation of Tgfilm for films down to 50 nm Thin exposed PMMA resist

Etch Rate vs. initial thickness • Etch Rate is decreasing as the initial film thickness declines • For initial thicknesses >150 nm ER gets its bulk value • ERbulk – ERthickn~50 nm>20 nm/min • Relative decrease of about 20% depending on the polymer Increased etch resistance of thin polymeric films Possible explanations for this are based on the effect of: • Sample heating (during process) • Physical properties of polymer (Free volume, Density, Diffusivity) N. Vourdas, A. G. Boudouvis, E. Gogolides Microelec. Eng. 78, 474(2005)

Multi Wavelength Dissolution Rate Monitor Spectrometer Characteristics • Low-Moderate sampling Rate (<50 samples/sec) • Need for fitting • Applicable to very thin films (>40 nm) • Allows detailed study of swelling Dissolution behaviour depends on film thickness Effect of Molecular Weight on dissolution A. Kokkinis, E. S. Valamontes, I. Raptis J. Physics (2005) “Dissolution properties of ultrathin photoresist films for the fabrication of nanostructures”

Conclusions / Future Plans Conclusions • Non destructive Optical methodologies were developed for the in-situ monitoring of the thin film properties. • Tgfilm in case of thin films are different from the bulk ones. Exposed and unexposed areas present different properties • Dissolution of thin films was studied. Results depend on the polymer/resist material. • Thin film issues are important for the sub 45 nm nodes Future Plans • Comparison of the three available optical methodologies for the Tgfilm calculation • Development processing conditions effect on the development rate of thin films • Thermal processing (PAB, PEB) effects on polymer/resist properties in the case of thin films