Submicron Radial Runout Error Compensation Method for the Turntable in a Wafer Prealigner

Abstract

In order to eliminate the influence of the radial runout error of the turntable on the prealignment precision of a wafer pre- aligner,an on-line detection and compensation method for the error is proposed.The mandrel above and rotating along with the turn- table is taken as the detecting component of the radial runout,and the radial distance of the mandrel is detected by a vortex sensor. The sensor's measurement value consists of fixed error and radial runout error,the former is solved off-line by means of ensemble average method or radial runout features of the turntable,based on which the radial runout error is separated from the data of the vortex sensor when working on-line.The radial runout error is used to compensate the peripheral data of the wafer detected by a laser displacement sensor with the compensation method simplified according to the error features.The experimentation has proved that the use of the radial runout compensation method has improved the prealignment precision of the system and made it meet the re- quirement of micron positioning precision.