Metrology for in-situ industrial plasma processing

Low-temperature plasmas (LTPs) already enable diverse technologies ranging from nano-electronics for electronic computer and mobile phone chips, spacecraft propulsion to
surgical devices. 'Cold' plasmas are weakly ionised and far from thermodynamic equilibrium; the electrons are hot (i.e. ~ 10,000 degrees), while the heavier ions and neutrals (dominant component) are close to room temperature. These plasmas efficiently produce reactive species, particularly free radicals e.g. atoms, that play a crucial role in surface interactions.

LTPs are extensively used in semiconductor manufacturing to create Integrated Circuits, and has enabled the continuation of Moore's law. Increased packing density of transistors grant more computing power, but critical dimensions have reached the atomic scale. Compounded by the fact that the etching of silicon chips are highly sensitive to changes in plasma parameters, the slightest deviation in etched features will have a significant impact on the performance of processors. Reproducibility between wafer batches is also essential to improve quality and efficiency. Thus, in order to better design and control the plasma-surface interaction, knowledge of the dynamics of these species is important. Sensors that probe the plasma-surface interface are critical to feed into design strategies for these processing applications.

The project will build on a developing sensor design concept that aims to provide information comparable to that of other diagnostic techniques, such as Two-photon Absorption Laser Induced Fluorescence (TALIF) and Energy Resolved Actinometry (ERA). However, these latter techniques are experimentally complex and expensive to adopt in an industrial setting. Thus, development of this simple, non-invasive sensor that can gather information inside the processing chamber is critical for real-time process control. Plasma operating conditions common to processing applications will be investigated, namely molecular electro-negative gases e.g. hydrogen and oxygen.