The resist spin-coating process

The diagrams in Fig. 11.4 show a schematic of the spin-coating process. The variables and coordinates used in developing the mathematical equations governing this flow are also indicated in the diagrams. 

The two main forces governing the spin-coating process are the viscous forces of the fluid that retard the expulsion of material from the wafer and centrifugal 

Polymer Interface and Adhesion, Marcel Dekker, New York (1982). 

Levinson, Principles of Lithography, 2nd ed., p. 59, SPIE Press, Bellingham, WA (2005). W.A. Zisman, Relation of equilibrium contact angle to liquid and solid constitution, in Contact Angle Wettability and Adhesion, Advances in Chemistry Series, Vol. 43, American Chemical Society, Washington, DC (1964). 

The terms on the right-hand side of Eq. (11.3) represent centrifugal force (mroi ) acting at a distance r from the rotation axis m is the mass of the liquid under consideration. This force creates a shear stress within the liquid, which is expressed as prco y, where y is the depth from the surface of the fluid. The terms on the left-hand side of Eq. (11.3), involving the radial velocity of the liquid at depth y, represent the viscous forces. 

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