i e a device maker etc or it can be coupled to an intranet at for example a vendor site i e an equipment manufacturer additionally for example controller 55 can be coupled to the internet furthermore another computer i e controller server etc can for example access controller 55 to exchange data via at least one of a direct connection an intranet and the internet the controller 55 also implements an algorithm for detection of an endpoint of an etch process being performed in plasma etch processing system 10 based on input data provided from light detection device 34 as described further herein the process of endpoint determination in accordance with an embodiment of the invention proceeds in two phases in the first phase optical emission spectroscopy oes data are acquired using light detection device 34 during one or more etch processing runs performed in a plasma etch processing system 10 such that a multivariate model can be established of the acquired optical emission spectroscopy oes data once the multivariate model of the optical emission spectroscopy oes data has been established it can be used in a second phase for in situ etch endpoint detection as long as the etch process being run during the second phase is reasonably similar in terms of structures being etched etch process conditions etch processing system used etc to those used in the one or more etch processing runs performed in the first phase this is to ensure the validity of multivariate model with reference now to fig2 where a flowchart 200 of the first phase is shown the process of setting up a multivariate model of the optical emission spectroscopy oes data.