In-situ electron density measurement in inductively coupled plasma using microwave reflectometer by Wi-Fi antenna on wafer

Among the characteristics of the low-temperature plasma often used in semiconductor processes, electron density plays an important role for understanding the plasma physics. Therefore, various studies involving invasive and non-invasive methods have been conducted to measure the electron density. This study aims to verify the possibility of measuring the electron density by simultaneously utilizing the characteristics of both invasive and non-invasive methods using a reflectometer attached to a commercial Wi-Fi antenna on a wafer in the vacuum chamber. The electron density was additionally measured using an interferometer and a single Langmuir probe under the same experimental conditions to assess the reliability of the reflectometer results, and the results were compared. The experiments were performed by increasing the 13.56 MHz radio frequency power applied to generate the plasma discharge in the 300 mm inductively coupled plasma bevel etcher equipment from 200 W to 400 W and 600 W, respectively. The electron densities measured using the three measurement methods (reflectometer/interferometer/single Langmuir probe) were confirmed to be in excellent agreement. Hence, the in-situ reflectometer on the wafer was verified to produce reliable results.