Ultrathin films and defectivity

Typical examples of UTR defects are shown in Fig. 11.11. The defects are categorized into four types, namely, COPs (associated with substrate imperfections), bubbles (associated with trapped gas), particles, and fall-on particles (the last two being associated with discrete particles of various sizes and origins). Bursting of bubbles of the kind shown in Fig. 11.11 will result in holes in the film (see Fig. 11.12). 

Other investigators reported pinhole defect density data that scale roughly with the inverse of the square of the film thickness, which can be derived from dynamic arguments, as was shown in Eq. (11.20). Spinodal decomposition dominates the nucleation process under clean room conditions, while particle nuclea-tion increases in higher aerosol concentration environments.  

Given the enhanced surface mobility, which is a consequence of the decreased surface density, and hence increased free volume of UTR film surfaces relative to the bulk and that of the film-substrate interfacial region, the lithographic properties of UTR films are bound to be dominated by interfacial effects. The surface region of such films is usually saturated with water or other solvents that can act as plasticizers. Thus, the Tg value of the surface chains can be further lowered with 

Garbassi, M. Morra, E. Ochiello, Polymer Surfaces From Physics to Technology, 2nd ed., John Wiley Sons, Hoboken, NJ (1998). 

Okoroanyanwu, Thin him instabilities and implications for ultra thin resist processes J. Vac. Sci. Technol. B 18(6), 3381 3387 (2000) U. Okoroanyanwu, Limits of ultra thin resist processes Future Fab. Int. 10, 157 163 (2001). ibid. 

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