Editing Sputtering (section)

==Applications and phenomena==

Sputtering only happens when the kinetic energy of the incoming particles is much higher than conventional thermal energies ([[Inequality (mathematics)|≫]] 1 [[Electronvolt|eV]]). When done with [[direct current]] (DC sputtering), voltages of 3-5 kV are used. When done with [[alternating current]] ([[Radio frequency|RF]] sputtering), frequencies are around the 14&nbsp;MHz range.

===Sputter cleaning===
Surfaces of solids can be cleaned from contaminants by using physical sputtering in a [[vacuum]]. Sputter cleaning is often used in [[surface science]], [[vacuum deposition]] and [[ion plating]]. In 1955 Farnsworth, Schlier, George, and Burger reported using sputter cleaning in an ultra-high-vacuum system to prepare ultra-clean surfaces for low-energy electron-diffraction (LEED) studies.<ref>{{cite journal | last1=Farnsworth | first1=H. E. | last2=Schlier | first2=R. E. | last3=George | first3=T. H. | last4=Burger | first4=R. M. | title=Ion Bombardment-Cleaning of Germanium and Titanium as Determined by Low-Energy Electron Diffraction | journal=Journal of Applied Physics | publisher=AIP Publishing | volume=26 | issue=2 | year=1955 | issn=0021-8979 | doi=10.1063/1.1721972 | pages=252–253| bibcode=1955JAP....26..252F }}</ref><ref>{{cite journal | last1=Farnsworth | first1=H. E. | last2=Schlier | first2=R. E. | last3=George | first3=T. H. | last4=Burger | first4=R. M. | title=Application of the Ion Bombardment Cleaning Method to Titanium, Germanium, Silicon, and Nickel as Determined by Low-Energy Electron Diffraction | journal=Journal of Applied Physics | publisher=AIP Publishing | volume=29 | issue=8 | year=1958 | issn=0021-8979 | doi=10.1063/1.1723393 | pages=1150–1161| bibcode=1958JAP....29.1150F }}</ref><ref>G.S. Anderson and Roger M. Moseson, “Method and Apparatus for Cleaning by Ionic Bombardment,” U.S. Patent #3,233,137 (filed Aug. 28, 1961) (Feb.1, 1966)</ref>  Sputter cleaning became an integral part of the [[ion plating]] process. When the surfaces to be cleaned are large, a similar technique, [[plasma cleaning]], can be used. Sputter cleaning has some potential problems such as overheating, gas incorporation in the surface region, bombardment (radiation) damage in the surface region, and the roughening of the surface, particularly if ''over done.'' It is important to have a ''clean'' [[Plasma (physics)|plasma]] in order to not continually recontaminate the surface during sputter cleaning. Redeposition of sputtered material on the substrate can also give problems, especially at high sputtering pressures. Sputtering of the surface of a compound or alloy material can result in the surface composition being changed. Often the species with the least mass or the highest [[vapor pressure]] is the one preferentially sputtered from the surface.

===Film deposition===
{{main|Sputter deposition}}
[[Sputter deposition]] is a method of [[thin film deposition|depositing]] [[thin film]]s by sputtering that involves eroding material from a "target" source onto a "substrate", e.g. a silicon [[wafer (semiconductor)|wafer]], solar cell, optical component, or many other possibilities.<ref>{{Cite news|url=https://www.admatinc.com/thinfilms/sputteringtarget/|title=Sputtering Targets {{!}} Thin Films|work=Admat Inc.|access-date=2018-08-28|language=en-US}}</ref> [[Resputtering]], in contrast, involves re-emission of the deposited material, e.g. SiO<sub>2</sub> during the deposition also by ion bombardment.

Sputtered atoms are ejected into the gas phase but are not in their [[thermodynamic equilibrium]] state, and tend to deposit on all surfaces in the vacuum chamber. A substrate (such as a wafer) placed in the chamber will be coated with a thin film. Sputtering deposition usually uses an [[argon]] plasma because argon, a noble gas, will not react with the target material.

=== Sputter damage ===
Sputter damage is usually defined during transparent electrode deposition on optoelectronic devices, which is usually originated  from the substrate's bombardment by highly energetic species. The main species involved in the process and the representative energies can be listed as (values taken from<ref name="Aydin 3549–3584">{{Cite journal|last1=Aydin|first1=Erkan|last2=Altinkaya|first2=Cesur|last3=Smirnov|first3=Yury|last4=Yaqin|first4=Muhammad A.|last5=Zanoni|first5=Kassio P. S.|last6=Paliwal|first6=Abhyuday|last7=Firdaus|first7=Yuliar|last8=Allen|first8=Thomas G.|last9=Anthopoulos|first9=Thomas D.|last10=Bolink|first10=Henk J.|last11=Morales-Masis|first11=Monica|author11-link= Mónica Morales Masis |date=2021-11-03|title=Sputtered transparent electrodes for optoelectronic devices: Induced damage and mitigation strategies|journal=Matter|language=English|volume=4|issue=11|pages=3549–3584|doi=10.1016/j.matt.2021.09.021|s2cid=243469180|issn=2590-2393|doi-access=free|hdl=10754/673293|hdl-access=free}}</ref>):

* Sputtered atoms (ions) from the target surface (~10 eV), the formation of which mainly depends on the binding energy of the target material;
* Negative ions (originating from the carrier gas) formed in the plasma (~5–15 eV), the formation of which mainly depends on the plasma potential;
* Negative ions formed at the target surface (up to 400 eV), the formation of which mainly depends on the target voltage;
* Positive ions formed in the plasma (~15 eV), the formation of which mainly depends on the potential fall in front of a substrate at floating potential;
* Reflected atoms and neutralized ions from the target surface (20–50 eV), the formation of which mainly depends on the background gas and the mass of the sputtered element.

As seen in the list above, negative ions (e.g., O<sup>−</sup> and In<sup>−</sup> for ITO sputtering) formed at the target surface and accelerated toward the substrate acquire the largest energy, which is determined by the potential between target and plasma potentials. Although the flux of the energetic particles is an important parameter, high-energy negative O<sup>−</sup> ions are additionally the most abundant species in plasma in case of reactive deposition of oxides. However, energies of other ions/atoms (e.g., Ar<sup>+</sup>, Ar<sup>0</sup>, or In<sup>0</sup>) in the discharge may already be sufficient to dissociate surface bonds or etch soft layers in certain device technologies.  In addition, the momentum transfer of high-energy particles from the plasma (Ar, oxygen ions) or sputtered from the target might impinge or even increase the substrate temperature sufficiently to trigger physical (e.g., etching) or thermal degradation of sensitive substrate layers (e.g. thin film metal halide perovskites).

This can affect the functional properties of underlying charge transport and passivation layers and photoactive absorbers or emitters, eroding device performance. For instance, due to sputter damage, there may be inevitable interfacial consequences such as pinning of the Fermi level, caused by damage-related interface gap states, resulting in the formation of Schottky-barrier impeding carrier transport. Sputter damage can also impair the doping efficiency of materials and the lifetime of excess charge carriers in photoactive materials; in some cases, depending on its extent, such damage can even lead to a reduced shunt resistance.<ref name="Aydin 3549–3584"/>

===Etching===
In the semiconductor industry sputtering is used to etch the target. Sputter etching is chosen in cases where a high degree of etching [[anisotropy]] is needed and selectivity is not a concern. One major drawback of this technique is wafer damage and high voltage use.

===For analysis===
Another application of sputtering is to etch away the target material. One such example occurs in [[secondary ion mass spectrometry]] (SIMS), where the target sample is sputtered at a constant rate. As the target is sputtered, the concentration and identity of sputtered atoms are measured using [[mass spectrometry]]. In this way the composition of the target material can be determined and even extremely low concentrations (20&nbsp;μg/kg) of impurities detected. Furthermore, because the sputtering continually etches deeper into the sample, concentration profiles as a function of depth can be measured.

===In space===
Sputtering is one of the forms of space weathering, a process that changes the physical and chemical properties of airless bodies, such as asteroids and the [[Moon]]. On icy moons, especially [[Europa (moon)|Europa]], sputtering of photolyzed water from the surface leads to net loss of hydrogen and accumulation of oxygen-rich materials that may be important for life. Sputtering is also one of the possible ways that [[Mars]] has lost most of its [[atmosphere]] and that [[Mercury (planet)|Mercury]] continually replenishes its tenuous surface-bounded [[exosphere]].

===Optics===
Due to its adaptability with a wide range of materials, Sputtering is used to create various types of coatings that enhance the performance of optical components.<ref>{{cite web |url=https://www.sputtertargets.net/blog/exploring-the-advantages-and-disadvantages-of-sputtering.html |title=Exploring the Advantages and Disadvantages of Sputtering |last=Green |first=Julissa |website=Stanford Advanced Materials |access-date=July 1, 2024}}</ref> [[Anti-reflective coating|Anti-reflective coatings]] are applied to [[lenses]] and optical instruments to minimize light reflection and increase light transmission, which improves clarity and reduces glare.<ref>{{cite journal |last1=Raut |first1=Hemant |last2=Ganesh |first2=V. |date=2011 |title=Anti-reflective coatings: A critical, in-depth review |journal=Energy & Environmental Science |volume=4 |issue=10 |page=3779-3804 |doi=10.1039/C1EE01297E}}</ref> Sputtering is also used to deposit reflective coatings on mirrors, ensuring high reflectivity and durability for applications such as [[telescopes]], [[cameras]], and laser systems.<ref>{{cite web |url=https://www.nacl.com/the-power-of-anti-reflective-coatings-on-ig4-and-ig6-substrates/ |title=The power of anti-reflective coatings on ig4 and ig6 substrates |last=Plats |first=Kelley |date=Oct 12, 2023 |website=NACL |access-date=July 1, 2024}}</ref>