December 1, 2000 Feature Article

Overview of Spin Coating

Chris E. Scott
Associate Professor of Polymer Engineering
Department of Materials Science and Engineering
Massachusetts Institute of Technology



Overview

Spin coating is the preferred method for application of thin, uniform films to flat substrates. This process is very simple, illustrated in Figure 1 at right. An excess amount of polymer solution is placed on the substrate. The substrate is then rotated at high speed in order to spread the fluid by centrifugal force. Rotation is continued for some time, with fluid being spun off the edges of the substrate, until the desired film thickness is achieved. The solvent is usually volatile, providing for its simultaneous evaporation.

This process is used extensively in microlithography for the manufacture of integrated circuits. A photoresist solution is applied to a wafer using spin coating followed by heating to remove the solvent. The polymer itself is photochemically active. A positive resist reacts with radiation to become more soluble. In contrast, a negative resist reacts with radiation to become less soluble. Thus, the use of masked radiation followed by selective removal of the irradiated or nonirradiated polymer provides for the establishmend of a detailed pattern on the surface.

Figure 1.


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