ICP vs ECR
ICP: Inductive Coupled Plasma
ECR: Electron Cyclotron Resonance
Up to ca 1985 the RIE technology (parallel plate reactor) could meet the typical demands for dry etching. With increasing understanding of the plasma etch processes it became clear, that such a configuration would not operate in the optimum processing range for high rates at low ion energies ("Bias"). In fact with conventional RIE the plasma/ ion density is coupled with the ion energy and depends on the applied power and the process pressure.
OPT started in 1985 to look for technologies to decouple the density and the energy of the ions. Driven by literature the market first looked at the so called "Electron Cyclotron Resonance" concept. One of the first commercially available ECR systems (for low damage III/ V etching) was installed in 1987 by OPT !
While the goals high rates and/ or low damage have been achieved in many cases, one also learned about the disadvantages of the ECR technology:
It turned out, that a much simpler technology as "Inductive Coupled Plasma" overcomes all of the above problems. Today all major suppliers of plasma equipment use the ICP or similar technologies for high rate/ low damage etch applications. ICP (as well as earlier ECR) also finds its applications in low temperature PECVD.
ICP sources can be operated over a wide pressure range (i e can also be
used as "remote" sources): 1 - 500 mtorr
The plasma density in most cases increases linear with power even up to high power levels.
OPTs ICP sources (ICP 65, ICP 180, ICP 380) are "true ICP sources" with (removable) ESS !