Plasma etcher

A plasma etcher, or etching tool, is a tool used in the production of semiconductor devices. A plasma etcher produces a plasma from a process gas, typically oxygen or a fluorine-bearing gas, using a high frequency electric field, typically 13.56 MHz. A silicon wafer is placed in the plasma etcher, and the air is evacuated from the process chamber using a system of vacuum pumps. Then a process gas is introduced at low pressure, and is excited into a plasma through dielectric breakdown.

Uses

Plasma can be used to grow a silicon dioxide film on a silicon wafer (using an oxygen plasma), or can be used to remove silicon dioxide by using a fluorine bearing gas. When used in conjunction with photolithography, silicon dioxide can be selectively applied or removed to trace paths for circuits.

For the formation of integrated circuits it is necessary to structure various layers. This can be done with a plasma etcher. Before etching, a photoresist is deposited on the surface, illuminated through a mask, and developed. The dry etch is then performed so that structured etching is achieved. After the process, the remaining photoresist has to be removed. This is also done in a special plasma etcher, called an asher.[1]

Dry etching allows a reproducible, uniform etching of all materials used in silicon and III-V semiconductor technology. By using inductively coupled plasma/reactive ion etching (ICP/RIE), even hardest materials like e.g. diamond can be nanostructured.[2][3]

Plasma etchers are also used for de-layering integrated circuits in failure analysis.

Plasma confinement

Industrial plasma etchers often feature plasma confinement to enable repeatable etch rates and precise spatial distributions in RF plasmas.[4] One method of confining plasmas is by using the properties of the Debye sheath, a near-surface layer in plasmas similar to the double layer in other fluids. For example, if the Debye sheath length on a slotted quartz part is at least half the width of the slot, the sheath will close off the slot and confine the plasma, while still permitting uncharged particles to pass through the slot.

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References
  1. http://www.pvatepla.com/en/products/plasma-systems/microwellen-plasma/photoresist-ashing/overview
  2. Radtke, Mariusz; Nelz, Richard; Slablab, Abdallah; Neu, Elke (2019-10-24). "Reliable Nanofabrication of Single-Crystal Diamond Photonic Nanostructures for Nanoscale Sensing". Micromachines. MDPI AG. 10 (11): 718. doi:10.3390/mi10110718. ISSN 2072-666X.
  3. Radtke, Mariusz; Render, Lara; Nelz, Richard; Neu, Elke (2019-11-21). "Plasma treatments and photonic nanostructures for shallow nitrogen vacancy centers in diamond". Optical Materials Express. The Optical Society. 9 (12): 4716. doi:10.1364/ome.9.004716. ISSN 2159-3930.
  4. http://www.eecs.berkeley.edu/~lieber/confinedphys20Apr05.pdf
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