End-point detection of polymer etching using Langmuir probes

The adequate determination of the end point of a plasma-etching process is very important for integrated circuit fabrication. In this paper, the autho rs propose a new method, making use of the floating potential, as determine d by a single Langmuir probe with a radio frequency (RF) choke, For the etc hing of a polymer film with an oxygen plasma using a reactive ion-etching s ystem, this method yields a reproducible and reliable signal, which was suc cessfully used to detect the end point for several wafers. It is better tha n the method using the de self-bias voltage as the end-point detection sign al, and approximately as good as when using emission spectrometry-at least when the resist area is larger than 4.4 cm(2)-whereas it uses a much cheape r equipment set. Langmuir probe measurements indicate that the floating pot ential changes are caused by several mechanisms: the average mass change, t he plasma density, the average electron temperature, and the electron energ y distribution all change after the end point of the etching.