Deep reactive-ion etching: Difference between revisions

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{{Short description|Highly anisotropic etch process}}

{{More citations needed|date=December 2009}}

'''Deep reactive-ion etching''' ('''DRIE''') is a special subclass of [[reactive-ion etching]] (RIE). It enables highly [[anisotropy|anisotropic]] [[etching (microfab)|etch]] process used to create deep penetration, steep-sided holes and trenches in [[wafer (semiconductor)|wafer]]s/substrates, typically with high [[aspect ratio (image)|aspect ratio]]s. It was developed for [[microelectromechanical systems]] (MEMS), which require these features, but is also used to excavate trenches for high-density [[capacitor]]s for [[dynamic random access memory|DRAM]] and more recently for creating through-silicon vias ([[Through-silicon via|TSVs]]) in advanced 3D wafer level packaging technology.

In DRIE, the substrate is placed inside a reactor, and several gases are introduced. A plasma is struck in the gas mixture which breaks the gas molecules into ions. The ions are accelerated towards, and react with the surface of the material being etched, forming another gaseous element. This is known as the chemical part of the reactive ion etching. There is also a physical part, if ions have enough energy, they can knock atoms out of the material to be etched without chemical reaction.

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==Applications==

Etching depth typically depends on the application:

* in [[DRAM]] memory circuits, capacitor trenches may be 10–20 µmμm deep,

* in MEMS, DRIE is used for anything from a few micrometers to 0.5 mm.

* in irregular chip dicing, DRIE is used with a novel hybrid soft/hard mask to achieve sub-millimeter etching to dice silicon dies into lego-like pieces with irregular shapes.<ref>{{cite journal | last1= Ghoneim | first1= Mohamed | last2 = Hussain | first2= Muhammad | title = Highly Manufacturable Deep (Sub-Millimeter) Etching Enabled High Aspect Ratio Complex Geometry Lego-Like Silicon Electronics| journal= Small | date= 1 February 2017 | doi=10.1002/smll.201601801 | pmid= 28145623 | volume=13 | issue= 16 | page=1601801| hdl= 10754/622865 | url= https://repository.kaust.edu.sa/bitstream/10754/622865/1/smll.201601801_R2.pdf | hdl-access= free }}</ref><ref>{{cite news | last= Mendis | first= Lakshini | title= Lego-like Electronics | newspaper= Nature Middle East | date= 14 February 2017 | doi= 10.1038/nmiddleeast.2017.34 }}</ref><ref>{{cite news | last= Berger | first= Michael | title=Lego like silicon electronics fabricated with hybrid etching masks | newspaper= Nanowerk | date= 6 February 2017 | url= http://www.nanowerk.com/spotlight/spotid=45763.php}}</ref>

* in flexible electronics, DRIE is used to make traditional monolithic CMOS devices flexible by reducing the thickness of silicon substrates to few to tens of micrometers.<ref>{{ cite journal | last1= Ghoneim | first1= Mohamed | first2=Nasir | last2=Alfaraj | first3=Galo | last3=Torres-Sevilla | first4=Hossain | last4=Fahad | first5=Muhammad | last5=Hussain | title=Out-of-Plane Strain Effects on Physically Flexible FinFET CMOS | journal=IEEE Transactions on Electron Devices | volume= 63 | issue= 7 | pages= 2657–2664 | date= July 2016 | doi=10.1109/ted.2016.2561239| hdl= 10754/610712 | bibcode= 2016ITED...63.2657G | s2cid= 26592108 | url= https://figshare.com/articles/journal_contribution/5048395 | hdl-access=free }}</ref><ref>{{ cite journal | first1= Mohamed T. | last1= Ghoneim | first2= Muhammad M. | last2= Hussain | title=Review on physically flexible nonvolatile memory for internet of everything electronics | journal= Electronics | volume= 4 | issue= 3 | pages= 424–479 | date=23 July 2015 | arxiv= 1606.08404 | doi= 10.3390/electronics4030424 | s2cid= 666307 | doi-access= free }}</ref><ref>{{cite journal | first1= Mohamed T. | last1= Ghoneim | first2= Muhammad M. | last2= Hussain | title=Study of harsh environment operation of flexible ferroelectric memory integrated with PZT and silicon fabric | journal=Applied Physics Letters | date=3 August 2015 | doi=10.1063/1.4927913 | volume=107 | issue= 5 | page=052904| hdl= 10754/565819 | url=https://repository.kaust.edu.sa/bitstream/10754/565819/1/1.4927913.pdf | bibcode= 2015ApPhL.107e2904G | hdl-access=free }}</ref><ref>{{cite journal | first1=Mohamed T. | last1=Ghoneim | first2=Jhonathan P. | last2=Rojas | first3=Chadwin D. | last3=Young | first4=Gennadi | last4=Bersuker | first5=Muhammad M. | last5=Hussain | title=Electrical Analysis of High Dielectric Constant Insulator and Metal Gate Metal Oxide Semiconductor Capacitors on Flexible Bulk Mono-Crystalline Silicon | journal= IEEE Transactions on Reliability | volume=64 | issue=2 | pages=579–585 | date=26 November 2014 | doi=10.1109/TR.2014.2371054 | s2cid=11483790 | url=https://figshare.com/articles/journal_contribution/5048398 }}</ref><ref>{{cite journal | first1=Mohamed T. | last1=Ghoneim | first2=Mohammed A. | last2=Zidan | first3=Mohammed Y. | last3=Alnassar | first4=Amir N. | last4=Hanna | first5=Jurgen | last5= Kosel | first6=Khaled N. | last6=Salama | first7=Muhammad | last7=Hussain | title=Flexible Electronics: Thin PZT-Based Ferroelectric Capacitors on Flexible Silicon for Nonvolatile Memory Applications | journal=Advanced Electronic Materials | date=15 June 2015 | doi=10.1002/aelm.201500045 | volume=1 | issue=6 | page=1500045| doi-access=free | s2cid=110038210 | url=https://figshare.com/articles/journal_contribution/5048353 }}</ref><ref>{{cite journal | first1=Mohamed T. | last1=Ghoneim |first2=Arwa | last2=Kutbee | first3=Farzan | last3=Ghodsi | first4=G. |last4=Bersuker | first5=Muhammad M. | last5=Hussain | title=Mechanical anomaly impact on metal–oxide–semiconductor capacitors on flexible silicon fabric | journal= Applied Physics Letters | date=9 June 2014 | doi=10.1063/1.4882647 | volume=104 | issue=23 | page=234104| hdl=10754/552155 | url=http://repository.kaust.edu.sa/kaust/bitstream/10754/552155/1/1.4882647.pdf | bibcode=2014ApPhL.104w4104G | s2cid=36842010 | hdl-access=free }}</ref>

DRIE is distinguished from RIE fromby its etch depth. Practical etch depths for RIE (as used in [[integrated circuit|IC]] manufacturing) would be limited to around 10&nbsp;µmμm at a rate up to 1&nbsp;µmμm/min, while DRIE can etch features much greater, up to 600&nbsp;µmμm or more with rates up to 20&nbsp;µmμm/min or more in some applications.

DRIE of glass requires high plasma power, which makes it difficult to find suitable mask materials for truly deep etching. Polysilicon and nickel are used for 10–50&nbsp;µmμm etched depths. In DRIE of polymers, Bosch process with alternating steps of SF₆ etching and C₄F₈ passivation take place. Metal masks can be used, however they are expensive to use since several additional photo and deposition steps are always required. Metal masks are not necessary however on various substrates (Si [up to 800&nbsp;µmμm], InP [up to 40&nbsp;µmμm] or glass [up to 12&nbsp;µmμm]) if using chemically amplified negative resists.

Gallium ion implantation can be used as etch mask in cryo-DRIE. Combined nanofabrication process of focused ion beam and cryo-DRIE was first reported by N Chekurov ''et al'' in their article "The fabrication of silicon nanostructures by local gallium implantation and cryogenic deep reactive ion etching".<ref>{{cite journal |last1=Chekurov |first1=N |last2=Grigoras |first2=K |last3=Peltonen |first3=A |last4=Franssila |first4=S |last5=Tittonen |first5=I |display-authors=2 |title=The fabrication of silicon nanostructures by local gallium implantation and cryogenic deep reactive ion etching |journal=Nanotechnology |date=11 February 2009 |volume=20 |issue=6 |pages=065307 |doi=10.1088/0957-4484/20/6/065307 |pmid=19417383 |bibcode=2009Nanot..20f5307C |s2cid=9717001 |url=https://www.researchgate.net/publication/24403592}}</ref>

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==See also==

*[[Microelectromechanical systems]]

*[[Reactive-ion etching]]

==References==