Dry etching
Encyclopedia
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. 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.
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. In conjunction with semiconductor
manufacturing, micromachining
and display production the removal of organic residues by oxygen plasmas is sometimes correctly described as a dry etch process. However, also the term plasma ashing
may be used.
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.
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
material, by exposing the material to a bombardment of ions (usually a plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
of reactive gases such as fluorocarbons, oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
, chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
, boron trichloride
Boron trichloride
Boron trichloride is a chemical compound with the formula BCl3. This colorless gas is a valuable reagent in organic synthesis. It is also dangerously reactive.-Production and properties:Boron reacts with halogens to give the corresponding trihalides...
; sometimes with addition of nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
, argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
, helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
and other gases) that dislodge portions of the material from the exposed surface. Unlike with many (but not all, see isotropic etching
Isotropic etching
In semiconductor technology isotropic etching is non-directional removal of material from a substrate via a chemical process using an etchant substance. The etchant may be a corrosive liquid or a chemically active ionized gas, known as a plasma....
) of the wet chemical etchants used in wet etching
Wet etching
Wet etching may refer to:*Industrial etching*Etching...
, the dry etching process typically etches directionally or anisotropically.
Explanation
Dry etching is used in conjunction with photolithographic techniquesPhotolithography
Photolithography is a process used in microfabrication to selectively remove parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical "photoresist", or simply "resist," on the substrate...
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
Semiconductor device
Semiconductor devices are electronic components that exploit the electronic properties of semiconductor materials, principally silicon, germanium, and gallium arsenide, as well as organic semiconductors. Semiconductor devices have replaced thermionic devices in most applications...
) or to otherwise remove portions of semiconductor layers where predominantly vertical sides are desired. In conjunction with semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
manufacturing, micromachining
Microelectromechanical systems
Microelectromechanical systems is the technology of very small mechanical devices driven by electricity; it merges at the nano-scale into nanoelectromechanical systems and nanotechnology...
and display production the removal of organic residues by oxygen plasmas is sometimes correctly described as a dry etch process. However, also the term plasma ashing
Plasma ashing
In semiconductor manufacturing plasma ashing is the process of removing the photoresist from an etched wafer. Using a plasma source, a monatomic reactive species is generated. Oxygen or fluorine are the most common reactive species...
may be used.
Dry etching is particularly useful for materials and semiconductors which are chemically resistant and could not be wet etched, such as silicon carbide
Silicon carbide
Silicon carbide , also known as carborundum, is a compound of silicon and carbon with chemical formula SiC. It occurs in nature as the extremely rare mineral moissanite. Silicon carbide powder has been mass-produced since 1893 for use as an abrasive...
or gallium nitride.