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.

See also

• Plasma etcher
• Etching (microfabrication)