Write short note on DRIE & its significance for MEMS device fabrication.
1 Answer

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.

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