Reactive ion etching (RIE) uses both physical and chemical mechanisms to achieve high levels of resolution. The process is one of the most diverse and most widely used processes in industry and research.

Since the process combines both physical and chemical interactions, the process is much faster.

The high energy collision from the ionization helps to dissociate the etchant molecules into more reactive species. An isotropic etch profile is possible as well as an anisotropic.

Therefore the RIE process, a chemical physical etch process, is the most important process in semiconductor manufacturing for structuring various films.

Inside the process chamber the wafer is placed on a high frequency electrode (HF electrode). By impact ionization plasma is generated in which free electrons as well as positively charged ions occur.

If the HF electrode is at a positive voltage the free electrons accumulate on it and cannot leave the electrode again because of their electron affinity. Thus the electrode charges up to -1000 V (BIAS voltage).

If the mean free path of the ions is high, the particles impact on the wafer surface in almost perpendicular direction.

Thus material is strike out of the surface by the accelerated ions (physical etching).

Lateral sidewalls are not affected and the etch profile remains anisotropic. By increasing the pressure in the etching chamber the mean free path of the particles is reduced. Therefore there are much more collisions and thus the particles are heading into various directions.

This causes a less directed etching, the etch process gets a more chemical character. The selectivity increases, the etch profile is more isotropic.