Advances in IEDF Measurements by Lock-in Detection

The distribution functions of the particles in a plasma provide the most complete description of its properties. Often the focus is on the distribution of the electrons, but the distribution of the ions can provide a wealth of information as well, such as the plasma and sheath potential, plasma density and electron temperature. The methods for experimentally obtaining the ion velocity distribution function (IVDF) have the added advantage of being essentially non-invasive. However, they usually lack the large dynamic range (several orders of magnitude) required for extracting this additional information.

In this contribution, we present a simple and inexpensive method that enables extending the capabilities of any retarding field energy analyzer device. The method is based on a harmonic modulation of the discriminating voltage and a lock-in detection. The implementation of the method together with an analysis of its accuracy are presented. The application of the system to obtaining the plasma parameters in an inductively coupled argon plasma is illustrated.