Abstract: Methods and systems for using a time-series of spectra to identify endpoint of a multi-step semiconductor fabrication processes such as multi-step deposition and multi-step etch processes. One method includes accessing a virtual carpet (e.g., a machine learning model) that is formed from a time-series of spectra for the multi-step processes collected during a training operation. During production, in-situ time-series of spectra are compared to the virtual carpet as part of end pointing of multi-step fabrication processes.