Spin coating
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Spin coating is a procedure used to apply uniform thin films to flat substrates. In short, an excess amount of the solvent is placed on the substrate, which is then rotated at high speed in order to spread the fluid by centrifugal force. Rotation is continued while the fluid spins off the edges of the substrate, until the desired thickness of the film is achieved. The applied solvent is usually volatile, and simultaneously evaporates. So, the higher the angular speed of spinning, the thinner the film. The thickness of the film also depends on the concentration of the solution and the solvent.
A device used for spin coating is called a spin coater, which are very popular in microlithography and the semiconductor industry. In principle, they consist of a high speed motor with a vacuum plate attached on the top. Spin coating can be used to create thin films with thicknesses below 10 nm.
Stages of spin coating
Although different engineers count things differently, there are four distinct stages to the spin coating process.
- Deposition of the coating fluid onto the wafer or substrate
- The substrate is accelerated up to its final, desired, rotation speed
- The substrate is spinning at a constant rate and fluid viscous forces dominate the fluid thinning behavior
- The substrate is spinning at a constant rate and solvent evaporation dominates the coating thinning behavior
References
- S. Middleman and A.K. Hochberg Process Engineering Analysis in Semiconductor Device Fabrication, McGraw-Hill, p. 313 (1993)
- Dirk W. Schubert, Thomas Dunkel; Spin coating from a molecular point of view: its concentration regimes, influence of molar mass and distribution; Materials Research Innovations Vol. 7, p. 314 (2003)
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