Summary and Conclusion

In sum, the most basic level of analysis is able to demonstrate why spin coating so often reliably produces a film of uniform thickness; it reproduces the usual experimental dependence of film thickness on spin speed; and in simple cases it can predict the final film thickness explicitly based only on process parameters and material properties. Defects and nonuniformities in spin coated films (Fig. 3) ultimately arise from neglected effects that become important in individual cases. One example is particulate dirt on a substrate, which can produce streaking as illustrated in Fig. 3a. For an ab initio investigation of process defects and nonuniformities, one may relax additional assumptions in the theoretical model, typically at the expense of an analytical solution.

For further reading, Acrivos et al. show that uniformity itself is not guaranteed for non-Newtonian liquids. [15] Moriarty et. al. begin to consider the effects of frontal propagation. [16] Bornside considers the effects of variation in composition, viscosity and diffusivity as a function of z. [17] Schwartz et. al. consider the inclusion of viscous, capillary, gravitational, centrifugal, Coriolis and finite contact angle effects, showing for example that one of the main causes of fingers during acceleration (Fig. 3b) is imperfect substrate wetting. [18]

© 2007 S. L. Hellstrom. The author grants permission to copy, distribute and display this work in unaltered form, with attributation to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.

References

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[11] F. Kreith, J. H. Taylor and J. P. Chong, "Heat and Mass Transfer from a Rotating Disk," J. Heat Trans., 81, 95 (1959).

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[13] ibid., "Mass Transfer, Flow, and Heat Transfer about a Rotating Disk," J. Heat Trans., 82, 294 (1960).

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[18] L. W. Schwartz and R. V. Roy, "Theoretical and Numerical Results for Spin Coating of Viscous Liquids," Phys. Fluids, 16, 569 (2004).