"Plasma emission monitoring (PEM) has been used for a number of years to either monitor the condition of or actively control vacuum plasma processes. This approach has many
advantages such as fast response time, monotonic sensor behaviour and the ability to control
uniformity by monitoring different areas of the process. There are however some
disadvantages, e.g. there is required a clear line of sight to the plasma that can be obscured by substrate movement, the PEM sensor can become coated by the deposited material and,
of course, it can be only be used when the process itself generates a plasma.
A new type of remote plasma generator has been developed, which when combined with
advances in miniature spectrometers can be used to perform optical plasma spectroscopy
over a wide pressure range of 1 mBar to 1E-6 mBar. Presented are a number of examples of
its use as an intelligent pressure gauge (penning pressure measurement in conjunction with
plasma spectroscopy), etching process monitoring, vacuum quality monitoring, and reactive
deposition control. A novel, pulsed power, method of enhancing the sputter effect inside the sensor has also been developed. This allows for use of the sputtered cathode emission as a secondary, indirect
indicator of the condition of the vacuum and state of the process, enabling monitoring and
control of processes otherwise not possible via conventional plasma spectroscopy.
Furthermore, this sputter mode of operation has the effect of “cleaning” the sensor’s cathode,
allowing for extended operation with processes that would otherwise damage the sensor.