The spinner is a wafer holder - motor combination used to apply a very thin layer of photoactive chemical to the surface of the wafer (the "photoresist"). The wafer is held on the spinner during photoresist application by vacuum suction. This allows the spinner to rotate the wafer at several thousand RPM.
For safety, the spinner top is closed before the spinning action is started. This ensures that stray photoresist or HMDS droplets are contained within the spinner enclosure. The circular opening in the spinner top is used for dispensing the chemicals.
