The influence of high negative substrate pulse bias on bulk plasma density

In this paper, we have used a dual Langmuir probe system to locate the edge of sheath and studied the influence of high negative pulse bias on bulk plasma density. Bulk plasma density changes greatly with and without substrate bias, but is insensitive to different non-zero substrate bias. Pulse width and frequency has greater influence on bulk plasma density, but there is not a simple linear increase between them, inflexion is observed with longer pulse width and higher frequency. We use two competitive interaction mechanisms --ionization cross sections and the secondary electron emission to explain the phenomenon above.