![]() If the total liquid is too small, the coating will not be complete. Ideally, the perfect amount of material is deposited, and very little is slung off the sides of the wafer. The duration and flow rate of the liquid is another important consideration. However, if the wafer is spun too quickly, it can lead to uniformity by streaking and even wafer breakage. If all other parameters are left constant, the faster the spin, the thinner the coating, as the centrifugal forces are stronger and overcome surface tension and van Der Waals forces more easily. The most obvious control is the rotational speed of the chuck. Spin coating controlsĮngineers have several controls that they can adjust to optimize spin coated thin films. This article will mostly discuss spin coating’s application in the semiconductor industry. To ensure a thin, and thus predictable layer of photoresist, spin coating is the method of choice. Each of these steps relies on a thin layer of photoresist, a chemical that bonds to the wafer or oxide layer and can be selectively exposed and removed. During the numerous steps a silicon wafer undergoes to transform sand into a computer chip, there are many lithography steps. The semiconductor industry uses more spin coatings than virtually anyone else. ![]() The spread of the droplets on the surface depends on the surface roughness and wettability, as well as the liquid properties, such as the surface tension. Once the wafer is up to speed, the liquid is dripped at a controlled flow rate onto the surface of the wafer. The chuck will either have a physical clamp or hold the wafer in place by pulling a vacuum against the backside of the wafer. A wafer is held in place by a rotating chuck, which then spins at a set rotational speed. ![]()
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