Abstract

A novel technique for monitoring the stress and etching depth during plasma etching, namely, white light diffractometry is presented. A small 2-D Ronchi depth grating is written on the wafer along with the IC pattern. The monitoring light beam illuminates the grating so that the relative light intensities and positions of different diffraction orders from the grating give the stress and etching depth information. Different etching depths give different relative intensities of diffraction orders. Moreover, the stress changing of the surface results in the width changing of the diffraction grating so that the relative positions of different diffraction orders give the information of stress. To achieve high accuracy, high sensitivity in a wide range of depth and stress, a white light source is used. Spectral data of diffraction are collected by a 2-D CCD detector array. The correlation between the collected data and the desired data makes it possible to precisely monitor and control the plasma etching process.

© 1991 Optical Society of America