Invited Paper PS1-TuA3
Ion Energy Distribution Measurements at the Substrate Location in Continuous-wave and Pulse Modulated Plasmas

Tuesday, October 29, 2013, 2:40 pm, Room 102 B

Low pressure plasmas are used extensively in modern industry to process substrates. Both etching and deposition processes are controlled by energetic ion bombardment of the substrate. As substrates become larger, feature sizes smaller and film properties more complex there is an increasing demand for accurate monitoring and control of the ion energy distribution. Ion energy measurements have been reported in the literature for many decades. The two most common instruments that have been used are the quadrupole mass spectrometer and the retarding field energy analyzer (RFEA). The simplicity of the RFEA has led to its widespread use in various applications. The focus of this talk will be on the recent advances in RFEA technology for ion energy measurements in different types of plasma processes. In most cases the substrate is processed using an electrical bias. The substrate holder may be powered with radio-frequency (RF), pulsed-RF, direct current (DC) or pulsed-DC electrical signals. This complicates the use of RFEAs for ion energy measurement at the substrate location. The presence of the RFEA must not disturb the electrical bias and the electrical bias must not impair the RFEA data acquisition. Here we present an electrically filtered RFEA technology that allows for deployment at the biased substrate location. The filtering allows the RFEA sensor to float at the electrical bias voltage. We will discuss a number of filter configurations that cover the many frequencies, waveform shapes and bias levels that can be encountered. We also discuss a special configuration that permits time resolved measurements of the ion energy at the biased substrates under certain conditions. A number of novel extensions to the standard technology will also be presented. Spatially resolved measurements of the ion energy at multiple locations (simultaneously) across 300mm and 450mm substrate holders, used for plasma etching, will be presented. This RFEA design gives important information about the spatial uniformity of the plasma process under various plasma conditions. An embodiment of the RFEA design which can be used to determine the ion angular distribution is presented. This technique uses an additional orifice with variable aspect ratio to scan the angular distribution of the in coming ions across the energy range. Measurement of the ion angular distribution is particularly important near the edge of substrates, where yield is often poor due to sheath curvature in this region. Finally, the first results of a novel RFEA configuration that enables discrimination of the different ion species in the bombarding energy distribution will be presented and discussed.