| 摘要 |
<p>An auto focus system is provided to effectively control a defocus caused by a step generated at the end of a wafer and a defocus caused by particles attached to the back surface of the wafer by finely adjusting the wafer while using piezo. A wafer holder(20) is installed on a wafer stage(10) to mount a wafer on the wafer stage. An optical system(40) is installed at one side of the wafer stage to irradiate light to the wafer. A piezo(70) is attached to the upper surface of the wafer holder, composed of a quadrilateral base plate and a cylindrical pin installed on the upper surface of the base plate wherein the center of the upper surface of the cylindrical pin expands or contracts. The piezo expands or contracts the center of its upper surface to make the wafer agree with a pitch disposed in a focus sensor(3) so that the wafer is transferred vertically. A controller(1) controls the expansion or contraction operation of the center of the upper surface according to position values of the pitch in the focus sensor. Focus control units are installed at regular intervals on the outer surface of the wafer holder to vertically drive the wafer holder. A reflection mirror(50) is installed under the optical system so that the light irradiated from the optical system is irradiated toward the wafer. Light passes through a reticle(60) in a manner that a pattern is formed in the wafer by the light irradiated from the optical system.</p> |
