Precision polishing system

Abstract

A precision polishing system able to polish samples to an accuracy within the submicron range is disclosed. The novel polishing system has applications in the semiconductor field for use in polishing silicon wafers during testing and quality control inspections. In the examination of failed wafers during the semiconductor manufacturing process, it is desirable to examine a cross section of the wafer at the point of failure. The polishing system of the present invention enables very accurate polishing of the wafer down to the submicron accuracy range. The sample is held is place by a gripper assembly which is attached to a polishing arm slideably connected to a fixed rail. The polishing arm is raised and lowered to polish the sample using a polishing wheel covered with a suitable abrasive. A video microscope attached to an object lens and a video camera provide images that are processed to control the polishing operation. The video microscope is mounted on a precision X-Y table to facilitate focusing and defect location of the sample in addition to forming part of the closed loop control of the polishing process. Two closed loop feedback control methods are utilized by the invention to achieve high polishing accuracies. The first utilizes electromechanical means to perform rough polishing of the sample. The second method utilizes digital image processing techniques to accurately control the movement of a polishing arm which holds the sample as it is polished.