Advanced EMICON (Emission Controller) system vs. traditional PEM (Plasma Emission Controller) system

A traditional PEM (Plasma Emission Monitor) system in charge of a closed loop control of a reactive sputtering process is well-known established in a variety of coating applications in decades. Normally a high sensitivity PMT (Photo-Multiplier Tube) detector amplifies the light signal coming from plasma zone filtered by a narrow band-pass filter or scattered by a grating system or a monochromator. A long narrow tube with a simple collimating lens installed in front of the filter to block the contamination to the lens from plasma particles typically is mounted very close to the plasma zone and it is suffering high temperature from plasma heating and severe coating on the surface. Along the light path, only the spectra information filtered is able to be monitored and a disadvantage is its band width of the filter is too large for spectra analysis and the control precision is also limited due to very poor optical resolution. Typically a good bandpass filter has CWL (Central Wavelength Length) +/- 2nm and FWHM (Full Width Half Maximum) 10+/-2nm.

An advanced spectroscopic EMICON (EMIssion CONtrol) system equips high precision linear arrayed CCD detector and some revolutionary optics along the light path from plasma zone to the detector. Optical resolution is easily achieved in less than 1.5nm. For some applications request higher optical resolution, a solution is available to obtain 10 times better as well. This is really good for the study of plasma species in the process. EMICON allows the monitoring by multiple line elements and different band spectra in the same LOS (Light-Of-Sight) simultaneously, which an user can easily tell the ratio among different ions, atoms and molecules those involved in the plasma reaction. With the merit of broad band spectral range, the characteristics and behaviors of plasma particles participated in the plasma reaction are realized in detail. To stabilize the plasma reaction, it is possible to establish a closed loop control with PID regression built-in function. An Online QC can be achieved as well through easy-to-use endpoint settings on the software.