Reactive Ion Etching:
- Reactive ion etching (RIE) uses mid-level RF power and mid-range pressure to combine both physical and chemical etching in one process.
- The positive ions from plasma bombard the wafer’s surface (physical etch) at the same time that the free radicals adsorb to the surface (chemical etch).
- This process program can control the amount of physical vs. chemical etch by adjusting the process pressure or RF power.
- An increase in RF power will increase the physical etch while an increase in process pressure will increase the rate of chemical etch.
- This process provides high selectivity ratio.
- It also produces anisotropic profiles.
Its ability to capitalize on the advantages of both physical and chemical etching makes RIE an invaluable tool in the manufacture of microsystems.
Need for DRIE:
- Plasma etching can produce deeper trenches, than wet etching, but with tapered angles.
- Tapered trenches are not desirable in many applications such as resonators.
The DRIE process can produce deep trenches with θ ≈ 0.
The DRIE process provides thin films of a few microns protective coatings on the side walls during the etching process.
- It involves use of high density plasma source.
- The process allows alternating process of plasma (ion) etching of the substrate material and the deposition of etching-protective material on the sidewalls.
Special polymers are frequently used for sidewall protective films.