Spin Coating of Photoresists

During spincoating, the centrifugal force of the substrate spinning with several 1.000 rounds per minute (rpm) distributes few ml of resist over the substrate. Advantages: The high resist film thickness homogeneity as well as the short coating times make spincoating the most-applied coating technique at least in microelectronics. The fact that the coated resist already lost a significant amount of its solvent after spin coating, no time-consuming delays have to be kept before further process steps (handling, softbake). Limitations and disadvantages: In case of non-rotation-symmetric substrates, the resist forms a pronounced edge bead near the substrate edges due to the strong air turbulences. On textured substrate, the attained edge coverage of the textures is rather small, and parts of the topology might not be coated at all. With only few %, the resist yield is comparable low.