View source for Plasma etching

{{Infobox technology
|image = Rieoperation.svg
|technology = Etching
|names = Dry etching
|equipment = [[:Category:Plasma etching equipment|List of plasma etching equipment]]
}}

Plasma etching is a form of [[plasma processing]] designed to [[etching|remove]] material from a sample using plasma discharges.  It is highly controllable and can be used to etch a wide variety of materials.  The most commonly used form of plasma etching is referred to in the microfabrication world as [[reactive ion etching]] (RIE).  However, there are other types of plasma etching, including [[plasma ashing]] and [[ion milling]].  For a detailed overview of plasma etching in the LNF, please review the [https://drive.google.com/file/d/0B76AgohVTgqdamFiaE1mRk9mVmM/preview?usp=sharing&resourcekey=0-yGk7A8kAmb0kQArcKPNlTQ Tech Talk]

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==Reactive ion etching==
{{main|Reactive ion etching}}

Reactive ion etching (RIE) is one of the most common forms of [[plasma etching]].  It typically uses a combination of chemically reactive elements and energetic ions to etch the desired material.  One major advantage to RIE over other forms of etching is that the process can be designed to be highly [[Isotropy|anisotropic]], allowing for much finer resolution and higher aspect ratios.

{{:Reactive ion etching}}
==Deep reactive ion etching==
{{main|Deep reactive ion etching}}

Deep reactive ion etching (DRIE) is a term used to describe RIE processes that are designed to achieve high (>10:1) aspect ratios or etch depths greater than several microns. One common process is the [[Wikipedia:Bosch process|Bosch process]].

{{:Deep reactive ion etching}}
==Plasma ashing==
{{main|Plasma ashing}}

Plasma ashing typically refers to the removal of organics, particularly [[photoresist]] from a sample using a plasma discharge.  These processes typically use [[oxygen]] as the main etch gas and sometimes require a high temperature to enhance the reactivity.

===YES-CV200RFS(E)===
The [[YES-CV200RFS(E)|YES-CV200RFS(E) (YES Plasma Stripper)]] is the primary plasma ashing equipment in the main cleanroom of the LNF.  Its primary uses are low-temperature [[plasma descum]] and high-temperature [[photoresist stripping|stripping]] of [[photoresist]] but can also be used to etch a wide variety of polymers as well as for [[sample cleaning]] and [[surface activation]].

==Ion milling==
{{main|Ion milling}}

Ion milling uses an ion beam (typically [[argon]]) to [[sputtering|sputter]] material from the surface of the sample. It has very low selectivity (typically 1:1) but can be used on any material, even [[inert metal]]s.

===Nanoquest II Ion Mill===
{{main|Nanoquest II Ion Mill}}
The Nanoquest II Ion Mill is a 22 cm ion source for milling up to 150 mm wafers. It can etch most materials including metals, ceramics, semiconductors, dielectrics, etc.

==Method of operation==
{{see also|Reactive ion etching#Method of operation}}

==Parameters==
Parameters that affect plasma etching characteristics include pressure, gas composition, and, [[plasma generation]] method, and generator power.

===Gas composition===
{{main|Plasma etching/Gases}}

The type and ratio of [[:Category:gases|gases]] used in a plasma etch is chosen depending on the material being etched, the [[etch mask|masking material]], and the [[etch stop]] material in order to achieve high [[selectivity]].

===Pressure===
Chamber pressure varies depending on the system and material being etched but typically ranges from 5 mTorr to 300 mTorr.  Typically, more physical etches and etches designed to be very vertical or to have high aspect ratios run at lower pressures, while more reactive etches will use a higher pressure to increase the density of the reactive gases.  Most plasma etching systems control the pressure in the chamber using a throttle valve on the exhaust port, allowing it to be accurately set regardless of the gases chosen.

===Plasma source and power===
The plasma generation source is critical to the function of the etch.  [[Plasma processing/Capacitively coupled plasmas|Capacitively]] and [[Plasma processing/Inductively coupled plasmas|inductively]] coupled RF plasmas are very common, particularly in [[RIE]], but certain applications may use microwave sources, [[Wikipedia:Electron_cyclotron_resonance|ECR]] sources, etc.  Additionally, while in RIE the sample is typically placed directly under the source, sometimes the sample may be placed more indirectly from the source, such as in [[plasma ashing]].
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===Sample temperature===
Some plasma etching systems allow for the temperature of the sample to be controlled.  For most processes, the sample is kept between 20-50°C and are actively cooled to prevent damage to the mask, which is often [[photoresist]].  A liquid nitrogen cooled chuck, such as on the [[Oxford ICP RIE]] can be used to perform [[cryogenic etching]].  Also, some etch processes (e.g. [[polymer]] etching) benefit from a heated chuck (can be up to 200°C).

==Complete tool list==
For a complete list of plasma etching equipment available at the LNF, please see [[:Category:Plasma etching equipment|list of plasma etching equipment]] or the specific plasma etching category, above.

<categorytree mode=pages>Plasma etching equipment</categorytree>

==See also==
* [[Plasma processing]]

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==Further reading==
* [http://lnf-wiki.eecs.umich.edu/wiki/User_Resources#LNF_Tech_Talks_.28technology_seminar_series.29 LNF Tech Talk for RIE]

[[Category:Plasma etching| ]]
[[Category:Plasma processing|Etching]]