Plasma processing has played a crucial and pivotal role in a number of industries, but probably one of the more significant has been the semiconductor sector. With plasma etching and surface treatment being key steps in wafer manufacturing, modest improvements in methods, methodologies, processes or control at the low level have very significant outcomes in the overall production of semiconductors and their varied uses. This work takes a multi-pronged approach from design and
analysis of recently developed radio emission spectra capture to system level data acquisition over multi-sensors (which includes novel sensor approaches) for insertion into a hierarchical time series database structure, built upon a novel message-based network bus subsystem. Early work focused on the development of an optical viewport to obtain a planar view of the plasma. This was followed by the development of the non-invasive E and B-field radio probe technique for plasma monitoring RES (Radio Emission Spectroscopy), leading to the development of two branches of the sensor: the time-domain (TRES) and the frequency-domain (FRES). The two techniques can be applied in parallel to the
commonly acquired data, but the processing techniques are somewhat different.
The investigation of arcing within the chamber, which is very much a transient event, lends itself to TRES processing. TRES processing is by the application of novel near field B- and E-field analysis to detect these time-variant events where the frequency variation is small. The continuous operation of the plasma can be observed by applying digital signal processing (DSP) techniques to the FRES data, where the main measurement is frequency variant and the time resolution is large.
Our approach is to use non-invasive measurement techniques from a range of sensors both in real time and in analytical modes. The analytical mode can be instantiated as an analysis technique, field-deployed, and as such can trigger a direct response to the process. The non-invasive sensors can be used as standalone to monitor operating processes and with simple thresholding can produce notifications of significant events.
The work on the development of the novel FRES and the TRES sensor systems led to the investigation of the underlying scientific principles for the emission of such waves when driven by a single frequency. This FRES and TRES sensor subsystem has also been a commercial success with the technology being taken up by major semiconductor manufacturers for the determination of plasma conditions while
processing wafers.
The combination of novel non-invasive sensors, the real time alarm notification, the analysis over the broad-spectrum data and the instantiation of analytic blocks permits a very powerful and cost-effective tool in the control, maintainability and accounting of the production of semiconductor devices in a modern plant.