Dry etching
Dry etching refers to the removal of material, typically a masked pattern of semiconductor material, by exposing the material to a bombardment of ions (usually a plasma of reactive gases such as fluorocarbons, oxygen, chlorine, boron trichloride; sometimes with addition of nitrogen, argon, helium and other gases) that dislodge portions of the material from the exposed surface. A common type of dry etching is reactive-ion etching. Unlike with many (but not all, see isotropic etching) of the wet chemical etchants used in wet etching, the dry etching process typically etches directionally or anisotropically.
Applications
Dry etching is used in conjunction with photolithographic techniques to attack certain areas of a semiconductor surface in order to form recesses in material, such as contact holes (which are contacts to the underlying semiconductor substrate) or via holes (which are holes that are formed to provide an interconnect path between conductive layers in the layered semiconductor device) or to otherwise remove portions of semiconductor layers where predominantly vertical sides are desired. Along with semiconductor manufacturing, micromachining and display production, the removal of organic residues by oxygen plasmas is sometimes correctly described as a dry etch process. The term plasma ashing can be used instead.
Dry etching is particularly useful for materials and semiconductors which are chemically resistant and could not be wet etched, such as silicon carbide or gallium nitride.
| Wet Etching | Dry Etching |
|---|---|
| highly selective | easy to start and stop |
| no damage to substrate | less sensitive to small changes in temperature |
| cheaper | more repeatable |
| may have anisotropies | |
| fewer particles in environment |
High aspect ratio structures
Dry etching is currently used in semiconductor fabrication processes due to its unique ability over wet etch to do anisotropic etching (removal of material) to create high aspect ratio structures (e.g. deep holes or capacitor trenches).
Hardware design
The dry etching hardware design basically involves a vacuum chamber, special gas delivery system, RF waveform generator and an exhaust system.