Chemical control of defect formation during spin-coating of sol-gels

Spin-coating is a simple process for rapidly depositing thin coatings onto relatively flat substrates. The substrate to be covered is held by some rotatable fixture (often using a vacuum to clamp the substrate in place) and the coating solution is deposited onto the surface; the action of spinning causes the solution to spread out and form a very uniform coating of the chosen material on the surface of the substrate. Unfortunately there are many defects that can form during the deposition process that can detract from the desired coating uniformity. Some defects can be avoided simply by installing careful clean-room practices: good chemical cleaning of substrates and good air filtration to prevent particulates. Other defects arise as a direct result of solvent evaporation induced by the air-flow field above the rapidly spinning substrate. These defects will be the focus of this chapter.