Plasma Diagnostics and Energy Transport of a dc Discharge Used for Sputtering

Abstract

An investigation of plasma properties and energy‐transport mechanisms within a dc anomalous glow discharge has been conducted, with particular reference to those processes operating in the vicinity of the anode. The objective of this work was to obtain more quantitative information about the species in the plasma contributing to the heating of substrates located on the anode during sputtering. Techniques employed in this study involved the use of Langmuir probes for the detection of low‐energy species, of an electrostatic analyzer for detection of high‐energy species within the plasma, and of temperature‐sensitive probes for energy‐flux measurements. The negative glow of the plasma was found to contain two electron‐energy distributions, one of density ∼2×10¹⁰ cm⁻³ and mean energy ∼0.6 eV, and the other ∼2×10⁸ cm⁻³ and ∼6 eV energy. A low‐energy positive‐ion population approximately balanced these densities. Under all operating conditions, the plasma potential was found to be a few volts positive with respect to ground. Energy‐flux measurements at the anode showed that the main source of energy was not from these populations in the plasma, however. Further examination of the discharge, using the electrostatic analyzer, revealed the presence of high‐energy secondary electrons emitted at, or in, the vicinity of the cathode. Many of these electrons penetrated to the anode with the full fall of cathode potential, and it was found that they were the cause of the initial rapid rise of substrate temperature on commencement of sputtering. Radiation from uncooled cathodes was also a source of energy at the anode, once equilibrium temperatures had been approached.