Editing Doping (semiconductor) (section)

==Techniques of doping and synthesis==

=== Doping during crystal growth ===

Some [[dopant]]s are added as the (usually [[silicon]]) [[boule (crystal)|boule]] is grown by [[Czochralski method]], giving each [[wafer (electronics)|wafer]] an almost uniform initial doping.<ref>{{cite book |doi=10.1007/978-94-009-0917-5_1 |chapter=Silicon Crystal Growth |title=Microelectronic Materials and Processes |date=1989 |last1=Lin |first1=W. |last2=Benson |first2=K. E. |pages=1–24 |isbn=978-0-7923-0154-7 }}</ref>

Alternately, synthesis of semiconductor devices may involve the use of [[Metalorganic vapour phase epitaxy|vapor-phase epitaxy]]. In vapor-phase epitaxy, a gas containing the dopant precursor can be introduced into the reactor. For example, in the case of n-type gas doping of  [[gallium arsenide]], [[hydrogen sulfide]] is added, and sulfur is incorporated into the structure.<ref name=Schubert>{{cite book|title= Doping in III-V Semiconductors |author= Schubert, E. F.|year=2005 |pages=241–243|publisher= Cambridge University Press|isbn=978-0-521-01784-8}}</ref> This process is characterized by a constant concentration of sulfur on the surface.<ref name=Middleman>{{cite book|title= Process Engineering Analysis in Semiconductor Device Fabrication|author= Middleman, S.|year=1993 |pages=29, 330–337|publisher= McGraw-Hill|isbn=978-0-07-041853-0}}</ref> In the case of semiconductors in general, only a very thin layer of the wafer needs to be doped in order to obtain the desired electronic properties.<ref name=Deen>{{cite book|title= Analysis of Transport Phenomena |author= Deen, William M.|year=1998 |pages=91–94|publisher= Oup USA|isbn=978-0-19-508494-8}}</ref>

=== Post-growth doping ===

To define circuit elements, selected areas — typically controlled by [[photolithography]]<ref>{{cite web|url=http://www.computerhistory.org/semiconductor/timeline/1955-Photolithography.html |title=Computer History Museum – The Silicon Engine{{pipe}}1955 – Photolithography Techniques Are Used to Make Silicon Devices |publisher=Computerhistory.org |access-date=2014-06-12}}</ref> — are further doped by such processes as thermal [[diffusion]] doping (tube furnace diffusion) <ref>{{cite web | title=1954: Diffusion Process Developed for Transistors | website=Computer History Museum | url=https://www.computerhistory.org/siliconengine/diffusion-process-developed-for-transistors/}}</ref> and [[ion implantation]], the latter method being more popular in large production runs for integrated circuits because of increased controllability.<ref name="ion-implantation-in-silicon-technology">{{cite journal |url=https://www.axcelis.com/wp-content/uploads/2019/02/Ion_Implantation_in_Silicon_Technology.pdf |title=Ion Implantation in Silicon Technology |first1=Leonard |last1=Rubin |first2=John |last2=Poate |journal=The Industrial Physicist |volume=9 |issue=3 |date=June–July 2003 |publisher=[[American Institute of Physics]] |pages=12–15}}</ref>

Thermal diffusion doping, simply known as diffusion, is widely used in silicon photovoltaics<ref>{{cite journal |last1=Saga |first1=Tatsuo |title=Advances in crystalline silicon solar cell technology for industrial mass production |journal=NPG Asia Materials |date=July 2010 |volume=2 |issue=3 |pages=96–102 |doi=10.1038/asiamat.2010.82 }}</ref> and uses chemicals such as [[Boron tribromide]] or [[diborane]]<ref name=":1">{{Cite web |title=CHAPTER 8: Diffusion |url=https://www.cityu.edu.hk/phy/appkchu/AP6120/8.PDF |website=www.cityu.edu.hk}}{{self-published inline|date=May 2025}}</ref> as a source for doping with boron.<ref>{{cite conference |doi=10.4229/EUPVSEC20202020-2CV.1.43 |date=2020 |last1=Lohmüller |first1=E. |last2=Glatz |first2=M. |last3=Lohmüller |first3=S. |last4=Belledin |first4=U. |last5=Mack |first5=S. |last6=Fellmeth |first6=T. |last7=Naber |first7=R.C.G. |last8=Wolf |first8=A. |title=BBr3 Diffusion: Process Optimization for High-Quality Emitters with Industrial Cycle Times |conference=37th European Photovoltaic Solar Energy Conference and Exhibition |pages=364–369 }}</ref><ref>{{cite journal |last1=Li |first1=Mengjie |last2=Ma |first2=Fa-Jun |last3=Peters |first3=Ian Marius |last4=Shetty |first4=Kishan Devappa |last5=Aberle |first5=Armin G. |last6=Hoex |first6=Bram |last7=Samudra |first7=Ganesh S. |title=Numerical Simulation of Doping Process by BBr3 Tube Diffusion for Industrial n -Type Silicon Wafer Solar Cells |journal=IEEE Journal of Photovoltaics |date=May 2017 |volume=7 |issue=3 |pages=755–762 |doi=10.1109/JPHOTOV.2017.2679342 }}</ref> With the diffusion process, the wafer is placed in a quartz tube furnace, using a quartz holder called a ''boat''<ref>{{cite book |doi=10.1007/978-981-99-2836-1_66 |chapter=Diffusion and Ion Implantation Equipment |title=Handbook of Integrated Circuit Industry |date=2024 |last1=Cheng |first1=Zhaoyang |last2=Liu |first2=Xiaozhen |last3=Xie |first3=Junyu |last4=Zuo |first4=Zhuliang |pages=1361–1382 |isbn=978-981-99-2835-4 }}</ref> at a temperature of 1200°C in which a chemical compound containing the dopant, such as Boron tribromide for doping with boron to create p-type semiconductor regions, or [[Phosphoryl chloride]] to create n-type regions,<ref>{{cite journal |last1=Park |first1=Chan-Hyuck |last2=Pan |first2=Han |last3=Ishikawa |first3=Yasuhiko |last4=Wada |first4=Kazumi |last5=Ahn |first5=Donghwan |title=N-type doping of germanium epilayer on silicon by ex-situ phosphorus diffusion based on POCl3 phosphosilicate glass |journal=Thin Solid Films |date=September 2018 |volume=662 |pages=1–5 |doi=10.1016/j.tsf.2018.07.028 |bibcode=2018TSF...662....1P }}</ref><ref>{{cite journal |last1=Li |first1=Hongzhao |last2=Kim |first2=Kyung |last3=Hallam |first3=Brett |last4=Hoex |first4=Bram |last5=Wenham |first5=Stuart |last6=Abbott |first6=Malcolm |title=POCl3 diffusion for industrial Si solar cell emitter formation |journal=Frontiers in Energy |date=March 2017 |volume=11 |issue=1 |pages=42–51 |doi=10.1007/s11708-016-0433-7 }}</ref> is introduced into the furnace. This creates a layer of the dopant on the surface of the wafer and this step is called pre-deposition. Then a second step, called drive-in, is performed in which the wafer is heated at a higher temperature of 1300°C to introduce the dopant into the structure of the wafer.<ref>{{cite web | url=https://www.azom.com/article.aspx?ArticleID=21657#:~:text=Pre%2Ddeposition%20and%20drive%2Din,1000%20to%201250oC | title=Why and How do We Dope Semiconductors? | date=9 May 2022 }}</ref> Diffusion can use solid, liquid or gaseous sources with dopant atoms, such as solid [[boron nitride]] for boron, [[arsenic trioxide]] for arsenic, liquid [[arsenic trichloride]], gaaseous [[arsine]] or [[phosphine]]. If using a gaseous source, it is carried to the furnace using a carrier gas such as nitrogen, and then allowed to decompose on the hot surface of the wafer, depositing the desired dopant, such as arsenic for example. If a liquid source is used, its vapors are carried to the furnace using nitrogen.<ref name=":1" /><ref>{{cite web | url=https://eee.poriyaan.in/topic/diffusion-process-of-ic-fabrication-11890/ | title=Diffusion process of IC fabrication }}{{self-published inline|date=May 2025}}</ref><ref>{{cite book |doi=10.1007/978-981-99-2836-1_66 |chapter=Diffusion and Ion Implantation Equipment |title=Handbook of Integrated Circuit Industry |date=2024 |last1=Cheng |first1=Zhaoyang |last2=Liu |first2=Xiaozhen |last3=Xie |first3=Junyu |last4=Zuo |first4=Zhuliang |pages=1361–1382 |isbn=978-981-99-2835-4 }}</ref> The furnace can be either horizontal or vertical.<ref>{{cite web | url=https://slideplayer.com/slide/3514659/ | title=Chapter 7 Dopant Diffusion - PPT video online download }}</ref>

=== Spin-on glass ===
Spin-on glass or spin-on dopant doping is a two-step process. First, a mixture of SiO<sub>2</sub> and dopants (in a solvent) is applied to a wafer surface by [[spin-coating]]. Then it is stripping and baked at a certain temperature in a furnace with constant nitrogen+oxygen flow.<ref>{{Cite web |title=Spin-on Glass |url=http://inside.mines.edu/~sagarwal/phgn435/SOD.htm |access-date=2022-12-22 |website=inside.mines.edu}}</ref>

===Neutron transmutation doping ===
{{See also|Neutron activation}}
[[Neutron]] [[nuclear transmutation|transmutation]] doping (NTD) is an unusual doping method for special applications. Most commonly, it is used to dope silicon n-type in high-power electronics and [[semiconductor detector]]s. It is based on the conversion of the Si-30 isotope into [[phosphorus]] atom by neutron absorption as follows:

<math chem display="block">^{30}\mathrm{Si} \, (n,\gamma) \, ^{31}\mathrm{Si} \rightarrow \, ^{31}\mathrm{P} + \beta^- \; (T_{1/2} = 2.62 \mathrm{h}). </math> 
In practice, the silicon is typically placed near a [[nuclear reactor]] to receive the neutrons. As neutrons continue to pass through the silicon, more and more phosphorus atoms are produced by transmutation, and therefore the doping becomes more and more strongly n-type. NTD is a far less common doping method than diffusion or ion implantation, but it has the advantage of creating an extremely uniform dopant distribution.<ref>{{cite book |last1=Baliga |first1=B. Jayant |title=Modern Power Devices |date=1987 |publisher=Wiley |isbn=978-0-471-81986-8 |page=32 }}</ref><ref>{{cite book |last1=Schmidt |first1=P. E. |last2=Vedde |first2=J. |chapter=High Resistivity NTD Production and Applications |pages=3–16 |chapter-url={{GBurl|jD7ZGk12fsgC|p=3}} |editor1-last=Claeys |editor1-first=Cor L. |title=Proceedings of the Fifth International Symposium on High Purity Silicon |date=1998 |publisher=The Electrochemical Society |isbn=978-1-56677-207-5 }}</ref>