Ion implantation
{{Short description|Use of ions to cause chemical changes}}
{{Use American English|date = February 2019}}
{{Use dmy dates|date=August 2021}}
Image:Ion implantation machine at LAAS 0521.jpg technological facility in Toulouse, France.]]
Ion implantation is a low-temperature process by which ions of one element are accelerated into a solid target, thereby changing the target's physical, chemical, or electrical properties. Ion implantation is used in semiconductor device fabrication and in metal finishing, as well as in materials science research. The ions can alter the elemental composition of the target (if the ions differ in composition from the target) if they stop and remain in the target. Ion implantation also causes chemical and physical changes when the ions impinge on the target at high energy. The crystal structure of the target can be damaged or even destroyed by the energetic collision cascades, and ions of sufficiently high energy (tens of MeV) can cause nuclear transmutation.
General principle
Image:ion implanter schematic.svg
Ion implantation equipment typically consists of an ion source, where ions of the desired element are produced, an accelerator, where the ions are electrostatically accelerated to a high energy or using radiofrequency, and a target chamber, where the ions impinge on a target, which is the material to be implanted. Thus ion implantation is a special case of particle radiation. Each ion is typically a single atom or molecule, and thus the actual amount of material implanted in the target is the integral over time of the ion current. This amount is called the dose. The currents supplied by implants are typically small (micro-amperes), and thus the dose which can be implanted in a reasonable amount of time is small. Therefore, ion implantation finds application in cases where the amount of chemical change required is small.
Typical ion energies are in the range of 10 to 500 keV (1,600 to 80,000 aJ). Energies in the range 1 to 10 keV (160 to 1,600 aJ) can be used, but result in a penetration of only a few nanometers or less. Energies lower than this result in very little damage to the target, and fall under the designation ion beam deposition. Higher energies can also be used: accelerators capable of 5 MeV (800,000 aJ) are common. However, there is often great structural damage to the target, and because the depth distribution is broad (Bragg peak), the net composition change at any point in the target will be small.
The energy of the ions, as well as the ion species and the composition of the target determine the depth of penetration of the ions in the solid: A monoenergetic ion beam will generally have a broad depth distribution. The average penetration depth is called the range of the ions. Under typical circumstances ion ranges will be between 10 nanometers and 1 micrometer. Thus, ion implantation is especially useful in cases where the chemical or structural change is desired to be near the surface of the target. Ions gradually lose their energy as they travel through the solid, both from occasional collisions with target atoms (which cause abrupt energy transfers) and from a mild drag from overlap of electron orbitals, which is a continuous process. The loss of ion energy in the target is called stopping and can be simulated with the binary collision approximation method.
Accelerator systems for ion implantation are generally classified into medium current (ion beam currents between 10 μA and ~2 mA), high current (ion beam currents up to ~30 mA), high energy (ion energies above 200 keV and up to 10 MeV), and very high dose (efficient implant of dose greater than 1016 ions/cm2).{{Cite web|title=Ion Implantation {{!}} Semiconductor Digest|url=https://sst.semiconductor-digest.com/2015/12/ion-implantation/|access-date=2021-06-21|language=en-US}}{{cite web |title=Ion Implantation in Silicon Technology |url=https://www.axcelis.com/wp-content/uploads/2019/02/Ion_Implantation_in_Silicon_Technology.pdf |access-date=2 March 2024}}{{cite book |doi=10.1007/978-3-540-45298-0_15 |chapter=Ion implantation in CMOS Technology: Machine Challenges |title=Ion Implantation and Synthesis of Materials |date=2006 |pages=213–238 |isbn=978-3-540-23674-0 }}
= Ion source =
All varieties of ion implantation beamline designs contain general groups of functional components (see image). The first major segment of an ion beamline includes an ion source used to generate the ion species. The source is closely coupled to biased electrodes for extraction of the ions into the beamline and most often to some means of selecting a particular ion species for transport into the main accelerator section.
The ion source is often made of materials with a high melting point such as tungsten, tungsten doped with lanthanum oxide, molybdenum and tantalum. Often, inside the ion source a plasma is created between two tungsten electrodes, called reflectors, using a gas often based on fluorine containing the ion to be implanted whether it is germanium, boron, or silicon, such as boron trifluoride,{{cite book | url=https://books.google.com/books?id=vqUSBwAAQBAJ&dq=bf3+ion+implantation&pg=PA76 | title=Ion Implantation: Basics to Device Fabrication | isbn=978-1-4615-2259-1 | last1=Rimini | first1=Emanuele | date=27 November 2013 | publisher=Springer }} boron difluoride,{{cite book |doi=10.1109/IIT.2014.6940042 |chapter=Improved ion source stability using H2 co-gas for fluoride based dopants |title=2014 20th International Conference on Ion Implantation Technology (IIT) |date=2014 |last1=Hsieh |first1=Tseh-Jen |last2=Colvin |first2=Neil |pages=1–4 |isbn=978-1-4799-5212-0 }} germanium tetrafluoride or silicon tetrafluoride.{{cite web | url=https://www.semiconductor-digest.com/source-materials-enable-the-evolution-of-the-ion-implantation-process/ | title=Source Materials Enable the Evolution of the Ion-Implantation Process | date=8 February 2020 }} Arsine gas or phosphine gas can be used in the ion source to provide arsenic or phosphorus respectively for implantation.{{cite book | url=https://books.google.com/books?id=nDhpLa1rl44C&dq=arsine+ion+implantation&pg=RA3-SA83-PA10 | title=Encyclopaedia of Occupational Health and Safety | isbn=978-92-2-109816-4 | last1=Stellman | first1=Jeanne Mager | date=28 February 1998 | publisher=International Labour Organization }} The ion source also has an indirectly heated cathode. Alternatively this heated cathode can be used as one of the reflectors, eliminating the need for a dedicated one,{{cite book | url=https://books.google.com/books?id=PsVVKz_hjBgC&dq=ion+source+repeller&pg=SA7-PA43 | isbn=978-1-4200-1766-3 | title=Handbook of Semiconductor Manufacturing Technology | date=19 December 2017 | publisher=CRC Press }}{{cite journal |last1=Horsky |first1=Thomas N. |title=Indirectly heated cathode arc discharge source for ion implantation of semiconductors |journal=Review of Scientific Instruments |date=April 1998 |volume=69 |issue=4 |pages=1688–1690 |doi=10.1063/1.1148866 |bibcode=1998RScI...69.1688H }}{{cite web|url=https://global-sei.com/technology/tr/bn73/pdf/73-03.pdf|title=History of Ion Implanter and Its Future Perspective|website=global-sei.com|first1=Masayasu|first2=Masao|last1=Tanjyo|last2=Naito|archive-url=https://web.archive.org/web/20241201191443/https://global-sei.com/technology/tr/bn73/pdf/73-03.pdf|archive-date=1 December 2024|url-status=live}} or a directly heated cathode is used.{{cite journal |last1=Sakai |first1=Shigeki |last2=Hamamoto |first2=Nariaki |last3=Inouchi |first3=Yutaka |last4=Umisedo |first4=Sei |last5=Miyamoto |first5=Naoki |title=Ion sources for ion implantation technology (invited) |journal=Review of Scientific Instruments |date=February 2014 |volume=85 |issue=2 |pages=02C313 |doi=10.1063/1.4852315 |pmid=24593650 |bibcode=2014RScI...85bC313S }}
Oxygen or oxide based gases such as carbon dioxide can also be used for ions such as carbon. Hydrogen or hydrogen with xenon, krypton or argon may be added to the plasma to delay the degradation of tungsten components due to the halogen cycle.{{cite book |doi=10.1109/IIT.2016.7882870 |chapter=Exemplary Ion Source for the Implanting of Halogen and Oxygen Based Dopant Gases |title=2016 21st International Conference on Ion Implantation Technology (IIT) |date=2016 |last1=Hsieh |first1=Tseh-Jen |last2=Colvin |first2=Neil K. |pages=1–4 |isbn=978-1-5090-2024-9 }}{{cite book |doi=10.1109/IIT.2014.6940042 |chapter=Improved ion source stability using H2 co-gas for fluoride based dopants |title=2014 20th International Conference on Ion Implantation Technology (IIT) |date=2014 |last1=Hsieh |first1=Tseh-Jen |last2=Colvin |first2=Neil |pages=1–4 |isbn=978-1-4799-5212-0 }} The hydrogen can come from a high pressure cylinder or from a hydrogen generator that uses electrolysis.{{cite web|url=https://www.axcelis.com/wp-content/uploads/2019/03/Production-Worthy-Al-beams-for-SiC-Applications.pdf|title=Production-worthy Al beams for SiC applications|website=www.axcelis.com|archive-url=https://web.archive.org/web/20240218233026/https://www.axcelis.com/wp-content/uploads/2019/03/Production-Worthy-Al-beams-for-SiC-Applications.pdf|archive-date=18 February 2024|url-status=live}}
Repellers at each end of the ion source continually move the atoms from one end of the ion source to the other, resembling two mirrors pointed at each other constantly reflecting light.
The ions are extracted from the source by an extraction electrode outside the ion source through a slit shaped aperture in the source,{{cite web|url=https://www.semitracks.com/newsletters/march/2012-march-newsletter.pdf|title=Ion Implanation Part 1 - Equipment|website=www.semitracks.com|publisher=Semitracks|first=Christopher|last=Henderson|archive-url=https://web.archive.org/web/20240218233025/https://www.semitracks.com/newsletters/march/2012-march-newsletter.pdf|archive-date=18 February 2024|url-status=live}}{{cite book |doi=10.1109/PAC.1991.164876 |chapter=Ion sources for commercial ion implanter applications |title=Conference Record of the 1991 IEEE Particle Accelerator Conference |date=1991 |last1=Walther |first1=S.R. |last2=Pedersen |first2=B.O. |last3=McKenna |first3=C.M. |pages=2088–2092 |isbn=0-7803-0135-8 }} then the ion beam then passes through an analysis magnet to select the ions that will be implanted and then passes through one or two{{cite journal |last1=Satoh |first1=Shu |last2=Platow |first2=Wilhelm |last3=Kondratenko |first3=Serguei |last4=Rubin |first4=Leonard |last5=Mayfield |first5=Patrick |last6=Lessard |first6=Ron |last7=Bonacorsi |first7=Genise |last8=Jen |first8=Causon |last9=Whalen |first9=Paul |last10=Newman |first10=Russ |title=Purion XEmax, Axcelis ultra-high energy implanter with Boost™ technology |journal=MRS Advances |date=10 January 2023 |volume=7 |issue=36 |pages=1490–1494 |doi=10.1557/s43580-022-00442-9 }} linear accelerators (linacs){{cite book |doi=10.1109/IIT.2018.8807986 |chapter=Review of Major Innovations in Beam Line Design |title=2018 22nd International Conference on Ion Implantation Technology (IIT) |date=2018 |last1=Glavish |first1=Hilton |last2=Farley |first2=Marvin |pages=9–18 |isbn=978-1-5386-6828-3 }} that accelerate the ions before they reach the wafer in a process chamber. In medium current ion implanters there is also a neutral ion trap before the process chamber to remove neutral ions from the ion beam.{{cite book | url=https://books.google.com/books?id=OfJuCh5hCcEC&dq=ion+implanter+neutral+beam+trap&pg=PA57 | isbn=978-0-471-79027-3 | title=Fundamentals of Semiconductor Manufacturing and Process Control | date=26 May 2006 | publisher=John Wiley & Sons }}
Some dopants such as aluminum, are often not provided to the ion source as a gas but as a solid compound based on Chlorine or Iodine that is vaporized in a nearby crucible such as Aluminium iodide or Aluminium chloride or as a solid sputtering target inside the ion source made of Aluminium oxide or Aluminium nitride. Implanting antimony often requires the use of a vaporizer attached to the ion source, in which antimony trifluoride, antimony trioxide, or solid antimony are vaporized in a crucible and a carrier gas is used to route the vapors to an adjacent ion source, although it can also be implanted from a gas containing fluorine such as antimony hexafluoride or vaporized from liquid antimony pentafluoride. Gallium, Selenium and Indium are often implanted from solid sources such as selenium dioxide for selenium although it can also be implanted from hydrogen selenide. Crucibles often last 60–100 hours and prevent ion implanters from changing recipes or process parameters in less than 20–30 minutes. Ion sources can often last 300 hours.{{cite book |doi=10.1109/IIT.2014.6940042 | chapter=Improved ion source stability using H2 co-gas for fluoride based dopants | title=2014 20th International Conference on Ion Implantation Technology (IIT) | date=2014 | last1=Hsieh | first1=Tseh-Jen | last2=Colvin | first2=Neil | pages=1–4 | isbn=978-1-4799-5212-0 }}
The "mass" selection (just like in mass spectrometer) is often accompanied by passage of the extracted ion beam through a magnetic field region with an exit path restricted by blocking apertures, or "slits", that allow only ions with a specific value of the product of mass and velocity/charge to continue down the beamline. If the target surface is larger than the ion beam diameter and a uniform distribution of implanted dose is desired over the target surface, then some combination of beam scanning and wafer motion is used. Finally, the implanted surface is coupled with some method for collecting the accumulated charge of the implanted ions so that the delivered dose can be measured in a continuous fashion and the implant process stopped at the desired dose level.{{cite book | first1=Robert W. | last1=Hamm | first2=Marianne E. | last2=Hamm | title=Industrial Accelerators and Their Applications | publisher=World Scientific | year=2012 | isbn=978-981-4307-04-8}}
Application in semiconductor device fabrication
=Doping=
Semiconductor doping with boron, phosphorus, or arsenic is a common application of ion implantation. When implanted in a semiconductor, each dopant atom can create a charge carrier in the semiconductor after annealing. A hole can be created for a p-type dopant, and an electron for an n-type dopant. This modifies the conductivity of the semiconductor in its vicinity. The technique is used, for example, for adjusting the threshold voltage of a MOSFET. Ion implantation is practical due to the high sensitivity of semiconductor devices to foreign atoms, as ion implantation does not deposit large numbers of atoms. Sometimes such as during the manufacturing of SiC devices, ion implantation is carried out while heating the SiC wafer to 500 °C.{{cite book |doi=10.1109/IWJT.2015.7467062 |chapter=High temperature ion implanter for SiC and Si devices |title=2015 15th International Workshop on Junction Technology (IWJT) |date=2015 |last1=Takahashi |first1=Naoya |last2=Itoi |first2=Suguru |last3=Nakashima |first3=Yoshiki |last4=Zhao |first4=Weijiang |last5=Onoda |first5=Hiroshi |last6=Sakai |first6=Shigeki |pages=6–7 |isbn=978-4-8634-8517-4 }} This is known as a hot implant and it is used to control damage to the surface of the semiconductor.{{cite book | url=https://books.google.com/books?id=vqUSBwAAQBAJ&dq=hot+ion+implantation&pg=PA152 | isbn=978-1-4615-2259-1 | title=Ion Implantation: Basics to Device Fabrication | date=27 November 2013 | publisher=Springer }}{{cite book |doi=10.1109/IIT.2014.6940037 |chapter=VIISta 900 3D: Advanced medium current implanter |title=2014 20th International Conference on Ion Implantation Technology (IIT) |date=2014 |last1=Sinclair |first1=Frank |last2=Olson |first2=Joe |last3=Rodier |first3=Dennis |last4=Eidukonis |first4=Alex |last5=Thanigaivelan |first5=Thirumal |last6=Todorov |first6=Stan |pages=1–4 |isbn=978-1-4799-5212-0 }}{{cite journal |last1=Kachurin |first1=G.A. |last2=Tyschenko |first2=I.E. |last3=Fedina |first3=L.I. |title=High-temperature ion implantation in silicon |journal=Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms |date=May 1992 |volume=68 |issue=1–4 |pages=323–330 |doi=10.1016/0168-583X(92)96103-6 |bibcode=1992NIMPB..68..323K }} Cryogenic implants (Cryo-implants) can have the same effect.{{cite book |doi=10.1109/IWJT.2010.5475003 |chapter=Device performance and yield — A new focus for ion implantation |title=2010 International Workshop on Junction Technology Extended Abstracts |date=2010 |last1=Renau |first1=Anthony |pages=1–6 |isbn=978-1-4244-5866-0 }}
The energies used in doping often vary from 1 KeV to 3 MeV and it is not possible to build an ion implanter capable of providing ions at any energy due to physical limitations. To increase the throughput of ion implanters, efforts have been made to increase the current of the beam created by the implanter. The beam can be scanned across the wafer magnetically, electrostatically,{{cite book |doi=10.1109/IIT.1999.812079 |chapter=Scanned beam uniformity control in the VIISta 810 ion implanter |title=1998 International Conference on Ion Implantation Technology. Proceedings (Cat. No.98EX144) |date=1998 |last1=Olson |first1=J.C. |last2=Renau |first2=A. |last3=Buff |first3=J. |volume=1 |pages=169–172 |isbn=0-7803-4538-X }} mechanically or with a combination of these techniques.{{cite web | url=https://patents.google.com/patent/US4494005A/en | title=Beam scanning control device for ion implantation system }}{{cite web|url=https://www.axcelis.com/wp-content/uploads/2019/03/IntroducingThePurionH_Vanderberg_FINAL.pdf|title=Introducing Purion H, a Scanned Spot Beam High Currnet Ion Implanter|website=www.axcelis.com|publisher=Axcelis Technologies|first1=Bo|first2=Patrick|first3=Edward|first4=Bruce|first5=Joseph|first6=Weston|last1=Vanderberg|last2=Heres|last3=Eisner|last4=Libby|last5=Valinski|last6=Huff|archive-url=https://web.archive.org/web/20241228221733/http://www.axcelis.com/wp-content/uploads/2019/03/IntroducingThePurionH_Vanderberg_FINAL.pdf|archive-date=28 December 2024|url-status=live}}{{cite book |doi=10.1007/978-3-642-69156-0_15 |chapter=Comparison of Beam Scanning Systems |title=Ion Implantation: Equipment and Techniques |date=1983 |last1=Turner |first1=N. |pages=126–142 |isbn=978-3-642-69158-4 }} A mass analyzer magnet is used to select the ions that will be implanted on the wafer.Current, Michael & Rubin, Leonard & Sinclair, Frank. (2018). Commercial Ion Implantation Systems. Ion implantation is also used in displays containing LTPS transistors.
Ion implantation was developed as a method of producing the p-n junction of photovoltaic devices in the late 1970s and early 1980s,{{cite conference |last1=Armini |first1=A. J. |last2=Bunker |first2=S. N. |last3=Spitzer |first3=M. B. |title=Non-mass-analyzed ion implantation equipment for high volume solar cell production |conference=16th Photovoltaic Specialists Conference |date=1982 |pages=895–899 |bibcode=1982pvsp.conf..895A }} along with the use of pulsed-electron beam for rapid annealing,{{cite journal |last1=Landis |first1=G. A. |last2=Armini |first2=A. J. |last3=Greenwald |first3=A. C. |last4=Kiesling |first4=R. A. |title=Apparatus and technique for pulsed electron beam annealing for solar cell production |journal=15th Photovoltaic Specialists Conference |date=1981 |pages=976–980 |bibcode=1981pvsp.conf..976L }} although pulsed-electron beam for rapid annealing has not to date been used for commercial production. Ion implantation is not used in most photovoltaic silicon cells, instead, thermal diffusion doping is used.{{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 }}
=Silicon on insulator=
=Mesotaxy=
Mesotaxy is the term for the growth of a crystallographically matching phase underneath the surface of the host crystal (compare to epitaxy, which is the growth of the matching phase on the surface of a substrate). In this process, ions are implanted at a high enough energy and dose into a material to create a layer of a second phase, and the temperature is controlled so that the crystal structure of the target is not destroyed. The crystal orientation of the layer can be engineered to match that of the target, even though the exact crystal structure and lattice constant may be very different. For example, after the implantation of nickel ions into a silicon wafer, a layer of nickel silicide can be grown in which the crystal orientation of the silicide matches that of the silicon.
Application in metal finishing
=Tool steel toughening=
Nitrogen or other ions can be implanted into a tool steel target (drill bits, for example). The structural change caused by the implantation produces a surface compression in the steel, which prevents crack propagation and thus makes the material more resistant to fracture. The chemical change can also make the tool more resistant to corrosion.
=Surface finishing=
In some applications, for example prosthetic devices such as artificial joints, it is desired to have surfaces very resistant to both chemical corrosion and wear due to friction. Ion implantation is used in such cases to engineer the surfaces of such devices for more reliable performance. As in the case of tool steels, the surface modification caused by ion implantation includes both a surface compression which prevents crack propagation and an alloying of the surface to make it more chemically resistant to corrosion.
Other applications
=Ion beam mixing=
Ion implantation can be used to achieve ion beam mixing, i.e. mixing up atoms of different elements at an interface. This may be useful for achieving graded interfaces or strengthening adhesion between layers of immiscible materials.
=Ion implantation-induced [[nanoparticle]] formation=
Ion implantation may be used to induce nano-dimensional particles in oxides such as sapphire and silica. The particles may be formed as a result of precipitation of the ion implanted species, they may be formed as a result of the production of a mixed oxide species that contains both the ion-implanted element and the oxide substrate, and they may be formed as a result of a reduction of the substrate, first reported by Hunt and Hampikian.{{cite journal|last1=Hunt|first1=Eden|last2=Hampikian|first2=Janet|title=Ion implantation-induced nanoscale particle formation in Al2O3 and SiO2 via reduction|journal=Acta Materialia|date=1999|volume=47|issue=5|pages=1497–1511|doi=10.1016/S1359-6454(99)00028-2|bibcode=1999AcMat..47.1497H}}{{cite journal|last1=Hunt|first1=Eden|last2=Hampikian|first2=Janet|title=Implantation parameters affecting aluminum nano-particle formation in alumina|journal=Journal of Materials Science|date=April 2001|volume=36|issue=8|pages=1963–1973|doi=10.1023/A:1017562311310|s2cid=134817579}}{{cite web|last1=Hunt|first1=Eden|last2=Hampikian|first2=Janet|title=Method for ion implantation induced embedded particle formation via reduction|url=http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=6294223.PN.&OS=PN/6294223&RS=PN/6294223|website=uspto.gov|publisher=USPTO|access-date=4 August 2017|archive-date=9 March 2020|archive-url=https://web.archive.org/web/20200309064900/http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/PTO/srchnum.htm&r=1&f=G&l=50&s1=6294223.PN.&OS=PN/6294223&RS=PN/6294223|url-status=dead}} Typical ion beam energies used to produce nanoparticles range from 50 to 150 keV, with ion fluences that range from 1016 to 1018 ions/cm2.{{cite journal|last1=Werner|first1=Z.|last2=Pisarek|first2=M.|last3=Barlak|first3=M.|last4=Ratajczak|first4=R.|last5=Starosta|first5=W.|last6=Piekoszewski|first6=J.|last7=Szymczyk|first7=W.|last8=Grotzschel|first8=R.|title=Chemical effects in Zr- and Co-implanted sapphire|journal=Vacuum|date=2009|volume=83|pages=S57–S60|doi=10.1016/j.vacuum.2009.01.022|bibcode=2009Vacuu..83S..57W}}{{cite journal|last1=Alves|first1=E.|last2=Marques|first2=C.|last3=da Silva|first3=R.C.|last4=Monteiro|first4=T.|last5=Soares|first5=J.|last6=McHargue|first6=C.|last7=Ononye|first7=L.C.|last8=Allard|first8=L.F|title=Structural and optical studies of Co and Ti implanted sapphire|journal=Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms|date=2003|volume=207|issue=1|pages=55–62|doi=10.1016/S0168-583X(03)00522-6|bibcode=2003NIMPB.207...55A}}{{cite journal |last1=Xiang |first1=X |last2=Zu |first2=X T |last3=Zhu |first3=S |last4=Wei |first4=Q M |last5=Zhang |first5=C F |last6=Sun |first6=K |last7=Wang |first7=L M |title=ZnO nanoparticles embedded in sapphire fabricated by ion implantation and annealing |journal=Nanotechnology |date=28 May 2006 |volume=17 |issue=10 |pages=2636–2640 |doi=10.1088/0957-4484/17/10/032 |pmid=21727517 |bibcode=2006Nanot..17.2636X |hdl=2027.42/49223 |hdl-access=free }}{{cite journal|last1=Mota-Santiago|first1=Pablo-Ernesto|last2=Crespo-Sosa|first2=Alejandro|last3=Jimenez-Hernandez|first3=Jose-Luis|last4=Silva-Pereyra|first4=Hector-Gabriel|last5=Reyes-Esqueda|first5=Jorge-Alejandro|last6=Oliver|first6=Alicia|title=Size characterisation of noble-metal nano-crystals formed in sapphire by ion irradiation and subsequent thermal annealing|journal=Applied Surface Science|date=2012|volume=259|pages=574–581|doi=10.1016/j.apsusc.2012.06.114|bibcode=2012ApSS..259..574M}}{{cite journal|last1=Stepanov|first1=A. L.|last2=Marques|first2=C.|last3=Alves|first3=E.|last4=da Silva|first4=R. C.|last5=Silva|first5=M. R.|last6=Ganeev|first6=R. A.|last7=Ryasnyansky|first7=A. I.|last8=Usmanov|first8=T.|title=Nonlinear optical properties of gold nanoparticles synthesized by ion implantation in sapphire matrix|journal=Technical Physics Letters|date=2005|volume=31|issue=8|pages=702–705|doi=10.1134/1.2035371|bibcode=2005TePhL..31..702S|s2cid=123688388}}{{cite journal|last1=McHargue|first1=C.J.|last2=Ren|first2=S.X.|last3=Hunn|first3=J.D|title=Nanometer-size dispersions of iron in sapphire prepared by ion implantation and annealing|journal=Materials Science and Engineering: A|date=1998|volume=253|issue=1|pages=1–7|doi=10.1016/S0921-5093(98)00722-9}}{{cite journal|last1=Xiang|first1=X.|last2=Zu|first2=X. T.|last3=Zhu|first3=S.|last4=Wang|first4=L. M.|title=Optical properties of metallic nanoparticles in Ni-ion-implanted α-Al2O3 single crystals|journal=Applied Physics Letters|date=2004|volume=84|issue=1|pages=52–54|doi=10.1063/1.1636817|bibcode=2004ApPhL..84...52X}}{{cite journal|last1=Sharma|first1=S. K.|last2=Pujari|first2=P. K.|title=Embedded Si nanoclusters in α-alumina synthesized by ion implantation: An investigation using depth dependent Doppler broadening spectroscopy|journal=Journal of Alloys and Compounds|date=2017|volume=715|pages=247–253|doi=10.1016/j.jallcom.2017.04.285}}{{cite journal |last1=Xiang |first1=X |last2=Zu |first2=X T |last3=Zhu |first3=S |last4=Wang |first4=L M |last5=Shutthanandan |first5=V |last6=Nachimuthu |first6=P |last7=Zhang |first7=Y |title=Photoluminescence of SnO 2 nanoparticles embedded in Al 2 O 3 |journal=Journal of Physics D: Applied Physics |date=21 November 2008 |volume=41 |issue=22 |pages=225102 |doi=10.1088/0022-3727/41/22/225102 |hdl=2027.42/64215 |hdl-access=free }} The table below summarizes some of the work that has been done in this field for a sapphire substrate. A wide variety of nanoparticles can be formed, with size ranges from 1 nm on up to 20 nm and with compositions that can contain the implanted species, combinations of the implanted ion and substrate, or that are comprised solely from the cation associated with the substrate.
Composite materials based on dielectrics such as sapphire that contain dispersed metal nanoparticles are promising materials for optoelectronics and nonlinear optics.
| class="wikitable" style="text-align:center" |
| ! Implanted Species
! Substrate ! Ion Beam Energy (keV) ! Fluence (ions/cm2) ! Post Implantation Heat Treatment ! Result ! Source |
| rowspan=6 | Produces Oxides that Contain the Implanted Ion
| Co | Al2O3 | 65 | 5*1017 | Annealing at 1400 °C | Forms Al2CoO4 spinel |
|---|
| Co
| α-Al2O3 | 150 | 2*1017 | Annealing at 1000 °C in oxidizing ambient | Forms Al2CoO4 spinel |
| Mg
| Al2O3 | 150 | 5*1016 | --- | Forms MgAl2O4 platelets |
| Sn
| α-Al2O3 | 60 | 1*1017 | Annealing in O2 atmosphere at 1000 °C for 1 hr | 30 nm SnO2 nanoparticles form |
| Zn
| α-Al2O3 | 48 | 1*1017 | Annealing in O2 atmosphere at 600 °C | ZnO nanoparticles form |
| Zr
| Al2O3 | 65 | 5*1017 | Annealing at 1400 °C | ZrO2 precipitates form |
| rowspan=10 | Produces Metallic Nanoparticles from Implanted Species
| Ag | α-Al2O3 | 1500, 2000 | 2*1016, 8*1016 | Annealing from 600 °C to 1100 °C in oxidizing, reducing, Ar or N2 atmospheres | Ag nanoparticles in Al2O3 matrix |
| Au
| α-Al2O3 | 160 | 0.6*1017, 1*1016 | 1 hr at 800 °C in air | Au nanoparticles in Al2O3 matrix |
| Au
| α-Al2O3 | 1500, 2000 | 2*1016, 8*1016 | Annealing from 600 °C to 1100 °C in oxidizing, reducing, Ar or N2 atmospheres | Au nanoparticles in Al2O3 matrix |
| Co
| α-Al2O3 | 150 | <5*1016 | Annealing at 1000 °C | Co nanoparticles in Al2O3 matrix |
| Co
| α-Al2O3 | 150 | 2*1017 | Annealing at 1000 °C in reducing ambient | Precipitation of metallic Co |
| Fe
| α-Al2O3 | 160 | 1*1016 to 2*1017 | Annealing for 1 hr from 700 °C to 1500 °C in reducing ambient | Fe nanocomposites |
| Ni
| α-Al2O3 | 64 | 1*1017 | --- | 1-5 nm Ni nanoparticles |
| Si
| α-Al2O3 | 50 | 2*1016, 8*1016 | Annealing at 500 °C or 1000 °C for 30 min | Si nanoparticles in Al2O3 |
| Sn
| α-Al2O3 | 60 | 1*1017 | --- | 15 nm tetragonal Sn nanoparticles |
| Ti
| α-Al2O3 | 100 | <5*1016 | Annealing at 1000 °C | Ti nanoparticles in Al2O3 |
| rowspan=3 | Produces Metallic Nanoparticles from Substrate
| Ca | Al2O3 | 150 | 5*1016 | --- | Al nanoparticles in amorphous matrix containing Al2O3 and CaO |
| Y
| Al2O3 | 150 | 5*1016 | --- | 10.7± 1.8 nm Al particles in amorphous matrix containing Al2O3 and Y2O3 |
| Y
| Al2O3 | 150 | 2.5*1016 | --- | 9.0± 1.2 nm Al particles in amorphous matrix containing Al2O3 and Y2O3 |
Problems with ion implantation
=Crystallographic damage=
Each individual ion produces many point defects in the target crystal on impact such as vacancies and interstitials. Vacancies are crystal lattice points unoccupied by an atom: in this case the ion collides with a target atom, resulting in transfer of a significant amount of energy to the target atom such that it leaves its crystal site. This target atom then itself becomes a projectile in the solid, and can cause successive collision events.
Interstitials result when such atoms (or the original ion itself) come to rest in the solid, but find no vacant space in the lattice to reside. These point defects can migrate and cluster with each other, resulting in dislocation loops and other defects.
=Damage recovery=
Because ion implantation causes damage to the crystal structure of the target which is often unwanted, ion implantation processing is often followed by a thermal annealing. This can be referred to as damage recovery.
=Amorphization=
The amount of crystallographic damage can be enough to completely amorphize the surface of the target: i.e. it can become an amorphous solid (such a solid produced from a melt is called a glass). In some cases, complete amorphization of a target is preferable to a highly defective crystal: An amorphized film can be regrown at a lower temperature than required to anneal a highly damaged crystal. Amorphisation of the substrate can occur as a result of the beam damage. For example, yttrium ion implantation into sapphire at an ion beam energy of 150 keV to a fluence of 5*1016 Y+/cm2 produces an amorphous glassy layer approximately 110 nm in thickness, measured from the outer surface. [Hunt, 1999]
=Sputtering=
Some of the collision events result in atoms being ejected (sputtered) from the surface, and thus ion implantation will slowly etch away a surface. The effect is only appreciable for very large doses.
=Ion channelling=
Image:Diamond structure.png direction, showing hexagonal ion channels.]]
If there is a crystallographic structure to the target, and especially in semiconductor substrates where the crystal structure is more open, particular crystallographic directions offer much lower stopping than other directions. The result is that the range of an ion can be much longer if the ion travels exactly along a particular direction, for example the <110> direction in silicon and other diamond cubic materials.{{Cite book|title=Materials science of thin films : deposition and structure|author=Ohring, Milton|date=2002|publisher=Academic Press|isbn=9780125249751|edition=2nd|location=San Diego, CA|oclc=162575935}} This effect is called ion channelling, and, like all the channelling effects, is highly nonlinear, with small variations from perfect orientation resulting in extreme differences in implantation depth. For this reason, most implantation is carried out a few degrees off-axis, where tiny alignment errors will have more predictable effects.
Ion channelling can be used directly in Rutherford backscattering and related techniques as an analytical method to determine the amount and depth profile of damage in crystalline thin film materials.
Safety
= Hazardous materials =
In fabricating wafers, toxic materials such as arsine and phosphine are often used in the ion implanter process. Other common carcinogenic, corrosive, flammable, or toxic elements include antimony, arsenic, phosphorus, and boron. Semiconductor fabrication facilities are highly automated, but residue of hazardous elements in machines can be encountered during servicing and in vacuum pump hardware.
= High voltages and particle accelerators =
High voltage power supplies used in ion accelerators necessary for ion implantation can pose a risk of electrical injury. In addition, high-energy atomic collisions can generate X-rays and, in some cases, other ionizing radiation and radionuclides. In addition to high voltage, particle accelerators such as radio frequency linear particle accelerators and laser wakefield plasma accelerators present other hazards.
See also
References
{{reflist}}
External links
{{Commons category|Ion implantation}}
{{Glass science}}
Category:Semiconductor device fabrication