Plasma etching is often considered a yield limiter in the manufacturing of Submicron integrated circuit devices. Much effort has been devoted to developing reliable models that relate the process outputs to variations in real-time sensor signals. These models, called chamber state models, allow semiconductor manufacturers to predict etch behavior. In this article, we propose to use optical emission spectroscopy (OES) as a real-time sensor to quantify and predict the etching performance in an integrated circuit manufacturing line. This method is especially useful in plasma processing because it provides in situ and real-time analysis without disturbing the plasma or interfering with the process. This study is based on an OES system that has been installed on an Applied Materials 5300 Centura dielectric etcher with a single optical fiber connected from the reactor viewport to a spectrograph. A designed experiment was performed on oxide test wafers. Several etch characteristics, including etch rate, within-wafer uniformity, and aspect-ratio dependent etching (ARDE), were modeled in this study. Various modeling techniques such as multivariate principle component analysis, and partial least squares were employed to relate the various OES signatures to etching performance. The results show that 87% of etch rate variation and more than 95% of the variation in within-wafer uniformity can be explained by these models, although the OES signals can only explain 65% of the variation in ARDE.