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Encyclopedia > Ion implantation

Ion implantation is a materials engineering process by which ions of a material can be implanted into another solid, thereby changing the physical properties of the solid. Ion implantation is used in semiconductor device fabrication and in metal finishing, as well as various applications in materials science research. The ions introduce both a chemical change in the target, in that they can be a different element than the target, and a structural change, in that the crystal structure of the target can be damaged or even destroyed. Materials engineering is a discipline related to materials science which focusses on materials design, processing techniques (casting, rolling, welding, ion implantation, crystal growth, thin film deposition, sintering, glassblowing, etc. ... ion (disambiguation) An ion is an atom or group of atoms with a net electric charge. ... Nasas Glenn Research Center clean room. ... The Materials Science Tetrahedron, which often also includes Characterization at the center Materials science is an interdisciplinary field involving the properties of matter and its applications to various areas of science and engineering. ... Enargite crystals In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ...

Ion implantation setup with mass separator
Ion implantation setup with mass separator

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, and a target chamber, where the ions impinge on a target, which is the material to be implanted. Each ion is typically a single atom, 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 implanters are typically small (microamperes), and thus the dose which can be implanted in a reasonable amount of time is small. Thus, ion implantation finds application in cases where the amount of chemical change required is small. Image File history File links Schematics of an mass separating implantation/deposition setup. ... Image File history File links Schematics of an mass separating implantation/deposition setup. ... An ion source is an electro-magnetic device that is used to create charged particles. ...


Typical ion energies are in the range of 2 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, the net composition change at any point in the target will be small. The electronvolt (symbol eV, or, rarely and incorrectly, ev) is a unit of energy. ... Ion Beam Deposition is a process of applying materials to a target through the application of an ion beam. ...


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.

Contents

Application in semiconductor device fabrication

Nasas Glenn Research Center clean room. ...

Doping

The introduction of dopants in a semiconductor is the most common application of ion implantation. Dopant ions such as boron, phosphorus or arsenic are generally created from a gas source, so that the purity of the source can be very high. These gases tend to be very hazardous. When implanted in a semiconductor, each dopant atom creates a charge carrier in the semiconductor (hole or electron, depending on if it is a p-type or n-type dopant), thus modifying the conductivity of the semiconductor in its vicinity. In semiconductor production, doping refers to the process of intentionally introducing impurities into an extremely pure (also referred to as intrinsic) semiconductor in order to change its electrical properties. ...


Silicon on Insulator

One prominent method for preparing silicon on insulator (SOI) substrates from conventional silicon substrates is the SIMOX (Separation by IMplantation of OXygen) process, wherein a buried high dose oxygen implant is converted to silicon oxide by a high temperature annealing process. Silicon on insulator (SOI) is a layered structure consisting of a thin layer of silicon, from 50 nm to 100 µm, which is created on an insulating substrate, which is usually sapphire or silicon with an insulating layer of silicon dioxide(SiO2) 80 nm to 3 µm thick on its... General Name, Symbol, Number silicon, Si, 14 Chemical series metalloids Group, Period, Block 14, 3, p Appearance as coarse powder, dark grey with bluish tinge Standard atomic weight 28. ... Annealing, in metallurgy and materials science, is a heat treatment wherein the microstructure of a material is altered, causing changes in its properties such as strength and hardness. ...


Wafer bonding is an alternative method for preparing SOI, where a thermally or chemically oxidized silicon substrate is physically bonded to a second substrate, after which the second substrate is partially removed, leaving behind an active region of a specified thickness. While second substrate removal is commonly achieved via conventional etch or polish techniques, the SmartCut method developed by SOITEC employs ion implantation followed by substrate cleavage to determine the thickness of the remaining substrate. Soitec is a French semiconductor manufacturer which is specialised in the production of Silicon-On-Insulator (SOI) wafers. ...


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. Epitaxy is the growth of crystals of one material on the crystal face of another (heteroepitaxy) or the same (homoepitaxy) material, such that the two materials have a defined relative structural orientation. ...


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 prevent 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 issues in 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. Wax and paraffin are amorphous. ... Glass can be made transparent and flat, or into other shapes and colors as shown in this sphere from the Verrerie of Brehat in Brittany. ...


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. Sputtering is a physical vapor deposition, PVD process whereby atoms in a solid target material are ejected into the gas phase due to bombardment of the material by energetic ions. ...


Ion channelling

A diamond cubic crystal viewed from the <110> direction, showing hexagonal ion channels.
A diamond cubic crystal viewed from the <110> 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. 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. There is no relation between this effect and ion channel of a cell membrane. Image File history File links Diamond_structure. ... Crystallography (from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and graphein = write) is the experimental science of determining the arrangement of atoms in solids. ... General Name, Symbol, Number silicon, Si, 14 Chemical series metalloids Group, Period, Block 14, 3, p Appearance as coarse powder, dark grey with bluish tinge Standard atomic weight 28. ... One unit cell of the diamond cubic crystal structure. ... There are very few or no other articles that link to this one. ... Ion channels are pore-forming proteins that help to establish and control the small voltage gradient that exists across the plasma membrane of all living cells (see cell potential) by allowing the flow of ions down their electrochemical gradient. ...


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. Rutherford backscattering (or RBS, for Rutherford Backscattering Spectrometry) is an analytical technique in materials science. ...


Hazardous Materials Note

In the ion implantation semiconductor fabrication process of wafers, it is important for the workers to minimize their exposure to the toxic materials used in the ion implanter process. Such hazardous elements, solid source and gasses are used, such as Arsine and Phosphine. For this reason, the semiconductor fabrication facilities are highly automated, and may feature negative pressure gas bottles safe delivery system (SDS). Other elements may include Antimony, Arsenic, Phosphorus, and Boron. Residue of these elements show up when the machine is opened to atmosphere, and can also be accumulated and found concentrated in the vacuum pumps hardware. It is important not to expose yourself to these carcinogenic, corrosive, flammable, and toxic elements. Many overlapping safety protocols must be used when handling these deadly compounds. Use safety, and do read MSDS's. It has been suggested that Wafer prober be merged into this article or section. ... Toxic redirects here, but this is also the name of a song by Britney Spears; see Toxic (song) Look up toxic and toxicity in Wiktionary, the free dictionary. ... Arsine, the simplest compound of arsenic, is AsH3. ... Phosphine is the common name for phosphorus hydride (PH3), also known by the IUPAC name phosphane and, occasionally, phosphamine. ... NASAs Glenn Research Center cleanroom. ... General Name, Symbol, Number antimony, Sb, 51 Chemical series metalloids Group, Period, Block 15, 5, p Appearance silvery lustrous grey Standard atomic weight 121. ... General Name, Symbol, Number arsenic, As, 33 Chemical series metalloids Group, Period, Block 15, 4, p Appearance metallic gray Standard atomic weight 74. ... General Name, Symbol, Number phosphorus, P, 15 Chemical series nonmetals Group, Period, Block 15, 3, p Appearance waxy white/ red/ black/ colorless Standard atomic weight 30. ... General Name, Symbol, Number boron, B, 5 Chemical series metalloids Group, Period, Block 13, 2, p Appearance black/brown Standard atomic weight 10. ... The hazard symbol for carcinogenic chemicals in the Globally Harmonized System. ... See corrosive for the hazard. ... Flammable or Flammability refers to the ease at which a substance will ignite, causing fire or combustion. ... // Toxic and Intoxicated redirect here – toxic has other uses, which can be found at Toxicity (disambiguation); for the state of being intoxicated by alcohol see Drunkenness. ... An example MSDS in a US format provides guidance for handling a hazardous substance and information on its composition and properties. ...


High Voltage Safety

High voltage power supplies in ion implantation equipment can pose a risk of electrocution. In addition, high-energy atomic collisions can, in some cases, generate radionuclides. Operators and Maintenance personnel should learn and follow the safety advice of the manufacturer and/or the institution responsible for the equipment. Prior to entry to high voltage area, terminal components must be grounded using a grounding stick. Next, power supplies should be locked in the off state and tagged to prevent unauthorized energizing.


Manufacturers of Ion Implantation Equipment

Applied Materials, Inc. ... Axcelis Technologies, Inc. ... Varian Semiconductor Equipment Associates, Inc. ...

External links

SHALOM


 
 

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