Chemical vapor deposition

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DC plasma (violet) enhances the growth of carbon nanotubes in laboratory-scale PECVD apparatus PICT0111.JPG
DC plasma (violet) enhances the growth of carbon nanotubes in laboratory-scale PECVD apparatus

Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high quality, high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films.

Vacuum deposition

Vacuum deposition is a family of processes used to deposit layers of material atom-by-atom or molecule-by-molecule on a solid surface. These processes operate at pressures well below atmospheric pressure. The deposited layers can range from a thickness of one atom up to millimeters, forming freestanding structures. Multiple layers of different materials can be used, for example to form optical coatings. The process can be qualified based on the vapor source; physical vapor deposition uses a liquid or solid source and chemical vapor deposition uses a chemical vapor.

Semiconductor industry specialized field of electrical industry

The semiconductor industry is the aggregate collection of companies engaged in the design and fabrication of semiconductor devices. It formed around 1960, once the fabrication of semiconductors became a viable business. It has since grown to be a $412.2 billion industry in 2017.

A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films is a fundamental step in many applications. A familiar example is the household mirror, which typically has a thin metal coating on the back of a sheet of glass to form a reflective interface. The process of silvering was once commonly used to produce mirrors, while more recently the metal layer is deposited using techniques such as sputtering. Advances in thin film deposition techniques during the 20th century have enabled a wide range of technological breakthroughs in areas such as magnetic recording media, electronic semiconductor devices, LEDs, optical coatings, hard coatings on cutting tools, and for both energy generation and storage. It is also being applied to pharmaceuticals, via thin-film drug delivery. A stack of thin films is called a multilayer.

Contents

In typical CVD, the wafer (substrate) is exposed to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired deposit. Frequently, volatile by-products are also produced, which are removed by gas flow through the reaction chamber.

Wafer (electronics) thin slice of semiconductor material used in the fabrication of integrated circuits

In electronics, a wafer is a thin slice of semiconductor, such as a crystalline silicon (c-Si), used for the fabrication of integrated circuits and, in photovoltaics, to manufacture solar cells. The wafer serves as the substrate for microelectronic devices built in and upon the wafer. It undergoes many microfabrication processes, such as doping, ion implantation, etching, thin-film deposition of various materials, and photolithographic patterning. Finally, the individual microcircuits are separated by wafer dicing and packaged as an integrated circuit.

Volatility (chemistry) Tendency of a substance to vaporize

In chemistry, volatility is a material quality which describes how readily a substance vaporizes. At a given temperature and pressure, a substance with high volatility is more likely to exist as a vapor, while a substance with low volatility is more likely to be a liquid or solid. Volatility can also describe the tendency of a vapor to condense into a liquid or solid; less volatile substances will more readily condense from a vapor than highly volatile ones. Differences in volatility can be observed by comparing how fast a group of substances evaporate when exposed to the atmosphere. A highly volatile substance such as rubbing alcohol will quickly evaporate, while a substance with low volatility such as vegetable oil will remain condensed. In general, solids are much less volatile than liquids, but there are some exceptions. Solids that sublime such as dry ice or iodine can vaporize at a similar rate as some liquids under standard conditions.

Chemical reaction Process that results in the interconversion of chemical species

A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms, with no change to the nuclei, and can often be described by a chemical equation. Nuclear chemistry is a sub-discipline of chemistry that involves the chemical reactions of unstable and radioactive elements where both electronic and nuclear changes can occur.

Microfabrication processes widely use CVD to deposit materials in various forms, including: monocrystalline, polycrystalline, amorphous, and epitaxial. These materials include: silicon (dioxide, carbide, nitride, oxynitride), carbon (fiber, nanofibers, nanotubes, diamond and graphene), fluorocarbons, filaments, tungsten, titanium nitride and various high-k dielectrics.

Microfabrication processes of fabrication of miniature structures

Microfabrication is the process of fabricating miniature structures of micrometre scales and smaller. Historically, the earliest microfabrication processes were used for integrated circuit fabrication, also known as "semiconductor manufacturing" or "semiconductor device fabrication". In the last two decades microelectromechanical systems (MEMS), microsystems, micromachines and their subfields, microfluidics/lab-on-a-chip, optical MEMS, RF MEMS, PowerMEMS, BioMEMS and their extension into nanoscale have re-used, adapted or extended microfabrication methods. Flat-panel displays and solar cells are also using similar techniques.

Single crystal material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries

A single crystal or monocrystalline solid is a material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries. The absence of the defects associated with grain boundaries can give monocrystals unique properties, particularly mechanical, optical and electrical, which can also be anisotropic, depending on the type of crystallographic structure. These properties, in addition to making them precious in some gems, are industrially used in technological applications, especially in optics and electronics.

Epitaxy crystal growth process

Epitaxy refers to the deposition of a crystalline overlayer on a crystalline substrate.

Types

Hot-wall thermal CVD (batch operation type) ThermalCVD.PNG
Hot-wall thermal CVD (batch operation type)
Plasma assisted CVD PlasmaCVD.PNG
Plasma assisted CVD

CVD is practiced in a variety of formats. These processes generally differ in the means by which chemical reactions are initiated.

Pascal (unit) SI unit of pressure

The pascal is the SI derived unit of pressure used to quantify internal pressure, stress, Young's modulus and ultimate tensile strength. It is defined as one newton per square metre. It is named after the French polymath Blaise Pascal.

The torr is a unit of pressure based on an absolute scale, now defined as exactly 1/760 of a standard atmosphere. Thus one torr is exactly 101325/760 pascals (≈ 133.32 Pa).

Ultra-high vacuum (UHV) is the vacuum regime characterised by pressures lower than about 10−7 pascal or 100 nanopascals. UHV conditions are created by pumping the gas out of a UHV chamber. At these low pressures the mean free path of a gas molecule is greater than approximately 40 km, so the gas is in free molecular flow, and gas molecules will collide with the chamber walls many times before colliding with each other. Almost all molecular interactions therefore take place on various surfaces in the chamber.

Most modern CVD is either LPCVD or UHVCVD.

Plasma processing is a plasma-based material processing technology that aims at modifying the chemical and physical properties of a surface.

Plasma-enhanced chemical vapor deposition Ultra thin coating process

Plasma-enhanced chemical vapor deposition (PECVD) is a chemical vapor deposition process used to deposit thin films from a gas state (vapor) to a solid state on a substrate. Chemical reactions are involved in the process, which occur after creation of a plasma of the reacting gases. The plasma is generally created by radio frequency (RF) frequency or direct current (DC) discharge between two electrodes, the space between which is filled with the reacting gases.

Plasma (physics) One of the four fundamental states of matter

Plasma is one of the four fundamental states of matter, and was first described by chemist Irving Langmuir in the 1920s. It consists of a gas of ions, atoms which have some of their orbital electrons removed, and free electrons. Plasma can be artificially generated by heating or subjecting a neutral gas to a strong electromagnetic field to the point where an ionized gaseous substance becomes increasingly electrically conductive, and long-range electromagnetic fields dominate the behaviour of the matter.

Uses

CVD is commonly used to deposit conformal films and augment substrate surfaces in ways that more traditional surface modification techniques are not capable of. CVD is extremely useful in the process of atomic layer deposition at depositing extremely thin layers of material. A variety of applications for such films exist. Gallium arsenide is used in some integrated circuits (ICs) and photovoltaic devices. Amorphous polysilicon is used in photovoltaic devices. Certain carbides and nitrides confer wear-resistance. [7] Polymerization by CVD, perhaps the most versatile of all applications, allows for super-thin coatings which possess some very desirable qualities, such as lubricity, hydrophobicity and weather-resistance to name a few. [8] CVD of metal-organic frameworks, a class of crystalline nanoporous materials, has recently been demonstrated. [9] Applications for these films are anticipated in gas sensing and low-k dielectrics CVD techniques are adventageous for membrane coatings as well, such as those in desalination or water treatment, as these coatings can be sufficiently uniform (conformal) and thin that they do not clog membrane pores. [10]

Commercially important materials prepared by CVD

Polysilicon

Polycrystalline silicon is deposited from trichlorosilane (SiHCl3) or silane (SiH4), using the following reactions: [11]

SiHCl3 → Si + Cl2 + HCl
SiH4 → Si + 2 H2

This reaction is usually performed in LPCVD systems, with either pure silane feedstock, or a solution of silane with 70–80% nitrogen. Temperatures between 600 and 650 °C and pressures between 25 and 150 Pa yield a growth rate between 10 and 20 nm per minute. An alternative process uses a hydrogen-based solution. The hydrogen reduces the growth rate, but the temperature is raised to 850 or even 1050 °C to compensate. Polysilicon may be grown directly with doping, if gases such as phosphine, arsine or diborane are added to the CVD chamber. Diborane increases the growth rate, but arsine and phosphine decrease it.

Silicon dioxide

Silicon dioxide (usually called simply "oxide" in the semiconductor industry) may be deposited by several different processes. Common source gases include silane and oxygen, dichlorosilane (SiCl2H2) and nitrous oxide [12] (N2O), or tetraethylorthosilicate (TEOS; Si(OC2H5)4). The reactions are as follows: [13]

SiH4 + O2 → SiO2 + 2 H2
SiCl2H2 + 2 N2O → SiO2 + 2 N2 + 2 HCl
Si(OC2H5)4 → SiO2 + byproducts

The choice of source gas depends on the thermal stability of the substrate; for instance, aluminium is sensitive to high temperature. Silane deposits between 300 and 500 °C, dichlorosilane at around 900 °C, and TEOS between 650 and 750 °C, resulting in a layer of low- temperature oxide (LTO). However, silane produces a lower-quality oxide than the other methods (lower dielectric strength, for instance), and it deposits nonconformally. Any of these reactions may be used in LPCVD, but the silane reaction is also done in APCVD. CVD oxide invariably has lower quality than thermal oxide, but thermal oxidation can only be used in the earliest stages of IC manufacturing.

Oxide may also be grown with impurities (alloying or "doping"). This may have two purposes. During further process steps that occur at high temperature, the impurities may diffuse from the oxide into adjacent layers (most notably silicon) and dope them. Oxides containing 5–15% impurities by mass are often used for this purpose. In addition, silicon dioxide alloyed with phosphorus pentoxide ("P-glass") can be used to smooth out uneven surfaces. P-glass softens and reflows at temperatures above 1000 °C. This process requires a phosphorus concentration of at least 6%, but concentrations above 8% can corrode aluminium. Phosphorus is deposited from phosphine gas and oxygen:

4 PH3 + 5 O2 → 2 P2O5 + 6 H2

Glasses containing both boron and phosphorus (borophosphosilicate glass, BPSG) undergo viscous flow at lower temperatures; around 850 °C is achievable with glasses containing around 5 weight % of both constituents, but stability in air can be difficult to achieve. Phosphorus oxide in high concentrations interacts with ambient moisture to produce phosphoric acid. Crystals of BPO4 can also precipitate from the flowing glass on cooling; these crystals are not readily etched in the standard reactive plasmas used to pattern oxides, and will result in circuit defects in integrated circuit manufacturing.

Besides these intentional impurities, CVD oxide may contain byproducts of the deposition. TEOS produces a relatively pure oxide, whereas silane introduces hydrogen impurities, and dichlorosilane introduces chlorine.

Lower temperature deposition of silicon dioxide and doped glasses from TEOS using ozone rather than oxygen has also been explored (350 to 500 °C). Ozone glasses have excellent conformality but tend to be hygroscopic – that is, they absorb water from the air due to the incorporation of silanol (Si-OH) in the glass. Infrared spectroscopy and mechanical strain as a function of temperature are valuable diagnostic tools for diagnosing such problems.

Silicon nitride

Silicon nitride is often used as an insulator and chemical barrier in manufacturing ICs. The following two reactions deposit silicon nitride from the gas phase:

3 SiH4 + 4 NH3 → Si3N4 + 12 H2
3 SiCl2H2 + 4 NH3 → Si3N4 + 6 HCl + 6 H2

Silicon nitride deposited by LPCVD contains up to 8% hydrogen. It also experiences strong tensile stress, which may crack films thicker than 200 nm. However, it has higher resistivity and dielectric strength than most insulators commonly available in microfabrication (1016 Ω·cm and 10 MV/cm, respectively).

Another two reactions may be used in plasma to deposit SiNH:

2 SiH4 + N2 → 2 SiNH + 3 H2
SiH4 + NH3 → SiNH + 3 H2

These films have much less tensile stress, but worse electrical properties (resistivity 106 to 1015 Ω·cm, and dielectric strength 1 to 5 MV/cm). [14]

Metals

CVD for tungsten is achieved from tungsten hexafluoride (WF6), which may be deposited in two ways:

WF6 → W + 3 F2
WF6 + 3 H2 → W + 6 HF

Other metals, notably aluminium and copper, can be deposited by CVD. As of 2010, commercially cost-effective CVD for copper did not exist, although volatile sources exist, such as Cu(hfac)2. Copper is typically deposited by electroplating. Aluminum can be deposited from triisobutylaluminium (TIBAL) and related organoaluminium compounds.

CVD for molybdenum, tantalum, titanium, nickel is widely used.[ citation needed ] These metals can form useful silicides when deposited onto silicon. Mo, Ta and Ti are deposited by LPCVD, from their pentachlorides. Nickel, molybdenum, and tungsten can be deposited at low temperatures from their carbonyl precursors. In general, for an arbitrary metal M, the chloride deposition reaction is as follows:

2 MCl5 + 5 H2 → 2 M + 10 HCl

whereas the carbonyl decomposition reaction can happen spontaneously under thermal treatment or acoustic cavitation and is as follows:

M(CO)n → M + n CO

the decomposition of metal carbonyls is often violently precipitated by moisture or air, where oxygen reacts with the metal precursor to form metal or metal oxide along with carbon dioxide.

Niobium(V) oxide layers can be produced by the thermal decomposition of niobium(V) ethoxide with the loss of diethyl ether [15] [16] according to the equation:

2 Nb(OC2H5)5 → Nb2O5 + 5 C2H5OC2H5

Graphene

Many variations of CVD can be utilized to synthesize graphene. Although many advancements have been made, the processes listed below are not commercially viable yet.

The most popular carbon source that is used to produce graphene is methane gas. One of the less popular choices is petroleum asphalt, notable for being inexpensive but more difficult to work with. [17]

Although methane is the most popular carbon source, hydrogen is required during the preparation process to promote carbon deposition on the substrate. If the flow ratio of methane and hydrogen are not appropriate, it will cause undesirable results. During the growth of graphene, the role of methane is to provide a carbon source, the role of hydrogen is to provide H atoms to corrode amorphous C, [18] and improve the quality of graphene. But excessive H atoms can also corrode graphene. [19] As a result, the integrity of the crystal lattice is destroyed, and the quality of graphene is deteriorated. [20] Therefore, by optimizing the flow rate of methane and hydrogen gases in the growth process, the quality of graphene can be improved.

The use of catalyst is viable in changing the physical process of graphene production. Notable examples include iron nanoparticles, nickel foam, and gallium vapor. These catalysts can either be used in situ during graphene buildup, [17] [21] or situated at some distance away at the deposition area. [22] Some catalysts require another step to remove them from the sample material. [21]

The direct growth of high-quality, large single-crystalline domains of graphene on a dielectric substrate is of vital importance for applications in electronics and optoelectronics. Combining the advantages of both catalytic CVD and the ultra-flat dielectric substrate, gaseous catalyst-assisted CVD [23] paves the way for synthesizing high-quality graphene for device applications while avoiding the transfer process.

Physical conditions such as surrounding pressure, temperature, carrier gas, and chamber material play a big role in production of graphene.

Most systems use LPCVD with pressures ranging from 1 to 1500 Pa. [17] [22] [24] [25] However, some still use APCVD. [21] Low pressures are used more commonly as they help prevent unwanted reactions and produce more uniform thickness of deposition on the substrate.

On the other hand, temperatures used range from 800–1050 °C. [17] [21] [22] [24] [25] High temperatures translate to an increase of the rate of reaction. Caution has to be exercised as high temperatures do pose higher danger levels in addition to greater energy costs.

Hydrogen gas and inert gases such as argon are flowed into the system. [17] [21] [22] [24] [25] These gases act as a carrier, enhancing surface reaction and improving reaction rate, thereby increasing deposition of graphene onto the substrate.

Standard quartz tubing and chambers are used in CVD of graphene. [17] [21] [22] [24] [25] Quartz is chosen because it has a very high melting point and is chemically inert. In other words, quartz does not interfere with any physical or chemical reactions regardless of the conditions.

Raman spectroscopy, X-ray spectroscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM) are used to examine and characterize the graphene samples. [17] [21] [22] [24] [25]

Raman spectroscopy is used to characterize and identify the graphene particles; X-ray spectroscopy is used to characterize chemical states; TEM is used to provide fine details regarding the internal composition of graphene; SEM is used to examine the surface and topography.

Sometimes, atomic force microscopy (AFM) is used to measure local properties such as friction and magnetism. [24] [25]

Cold wall CVD technique can be used to study the underlying surface science involved in graphene nucleation and growth as it allows unprecedented control of process parameters like gas flow rates, temperature and pressure as demonstrated in a recent study. The study was carried out in a home-built vertical cold wall system utilizing resistive heating by passing direct current through the substrate. It provided conclusive insight into a typical surface-mediated nucleation and growth mechanism involved in two-dimensional materials grown using catalytic CVD under conditions sought out in the semiconductor industry. [26] [27]

Graphene nanoribbon

In spite of graphene's exciting electronic and thermal properties, it is unsuitable as a transistor for future digital devices, due to the absence of a bandgap between the conduction and valence bands. This makes it impossible to switch between on and off states with respect to electron flow. Scaling things down, graphene nanoribbons of less than 10 nm in width do exhibit electronic bandgaps and are therefore potential candidates for digital devices. Precise control over their dimensions, and hence electronic properties, however, represents a challenging goal, and the ribbons typically possess rough edges that are detrimental to their performance.

Diamond

Free-standing single-crystal CVD diamond disc Single-crystal CVD diamond disc.jpg
Free-standing single-crystal CVD diamond disc
Colorless gem cut from diamond grown by chemical vapor deposition Apollo synthetic diamond.jpg
Colorless gem cut from diamond grown by chemical vapor deposition

CVD can be used to produce a synthetic diamond by creating the circumstances necessary for carbon atoms in a gas to settle on a substrate in crystalline form. CVD of diamonds has received much attention in the materials sciences because it allows many new applications that had previously been considered too expensive. CVD diamond growth typically occurs under low pressure (1–27 kPa; 0.145–3.926 psi; 7.5–203 Torr) and involves feeding varying amounts of gases into a chamber, energizing them and providing conditions for diamond growth on the substrate. The gases always include a carbon source, and typically include hydrogen as well, though the amounts used vary greatly depending on the type of diamond being grown. Energy sources include hot filament, microwave power, and arc discharges, among others. The energy source is intended to generate a plasma in which the gases are broken down and more complex chemistries occur. The actual chemical process for diamond growth is still under study and is complicated by the very wide variety of diamond growth processes used.

Using CVD, films of diamond can be grown over large areas of substrate with control over the properties of the diamond produced. In the past, when high pressure high temperature (HPHT) techniques were used to produce a diamond, the result was typically very small free standing diamonds of varying sizes. With CVD diamond growth areas of greater than fifteen centimeters (six inches) diameter have been achieved and much larger areas are likely to be successfully coated with diamond in the future. Improving this process is key to enabling several important applications.

The growth of diamond directly on a substrate allows the addition of many of diamond's important qualities to other materials. Since diamond has the highest thermal conductivity of any bulk material, layering diamond onto high heat producing electronics (such as optics and transistors) allows the diamond to be used as a heat sink. [28] [29] Diamond films are being grown on valve rings, cutting tools, and other objects that benefit from diamond's hardness and exceedingly low wear rate. In each case the diamond growth must be carefully done to achieve the necessary adhesion onto the substrate. Diamond's very high scratch resistance and thermal conductivity, combined with a lower coefficient of thermal expansion than Pyrex glass, a coefficient of friction close to that of Teflon (polytetrafluoroethylene) and strong lipophilicity would make it a nearly ideal non-stick coating for cookware if large substrate areas could be coated economically.

CVD growth allows one to control the properties of the diamond produced. In the area of diamond growth, the word "diamond" is used as a description of any material primarily made up of sp3-bonded carbon, and there are many different types of diamond included in this. By regulating the processing parameters—especially the gases introduced, but also including the pressure the system is operated under, the temperature of the diamond, and the method of generating plasma—many different materials that can be considered diamond can be made. Single crystal diamond can be made containing various dopants. [30] Polycrystalline diamond consisting of grain sizes from several nanometers to several micrometers can be grown. [28] [31] Some polycrystalline diamond grains are surrounded by thin, non-diamond carbon, while others are not. These different factors affect the diamond's hardness, smoothness, conductivity, optical properties and more.

Chalcogenides

Commercially, mercury cadmium telluride is of continuing interest for detection of infrared radiation. Consisting of an alloy of CdTe and HgTe, this material can be prepared from the dimethyl derivatives of the respective elements.

See also

Related Research Articles

Microelectromechanical systems technology of very small devices

Microelectromechanical systems is the technology of microscopic devices, particularly those with moving parts. It merges at the nano-scale into nanoelectromechanical systems (NEMS) and nanotechnology. MEMS are also referred to as micromachines in Japan, or micro systems technology (MST) in Europe.

Silane is an inorganic compound with chemical formula, SiH4, making it a group 14 hydride. It is a colourless, pyrophoric gas with a sharp, repulsive smell, somewhat similar to that of acetic acid. Silane is of practical interest as a precursor to elemental silicon.

Silicon carbide semiconductor containing silicon and carbon

Silicon carbide (SiC), also known as carborundum, is a semiconductor containing silicon and carbon. It occurs in nature as the extremely rare mineral moissanite. Synthetic SiC powder has been mass-produced since 1893 for use as an abrasive. Grains of silicon carbide can be bonded together by sintering to form very hard ceramics that are widely used in applications requiring high endurance, such as car brakes, car clutches and ceramic plates in bulletproof vests. Electronic applications of silicon carbide such as light-emitting diodes (LEDs) and detectors in early radios were first demonstrated around 1907. SiC is used in semiconductor electronics devices that operate at high temperatures or high voltages, or both. Large single crystals of silicon carbide can be grown by the Lely method and they can be cut into gems known as synthetic moissanite.

Tungsten(VI) fluoride, also known as tungsten hexafluoride, is an inorganic compound with the formula WF6. It is a toxic, corrosive, colorless gas, with a density of about 13 g/L (roughly 11 times heavier than air.) It is one of the densest known gases under standard conditions. WF6 is commonly used by the semiconductor industry to form tungsten films, through the process of chemical vapor deposition. This layer serves as a low-resistivity metallic "interconnect". It is one of seventeen known binary hexafluorides.

Atomic layer deposition

Atomic layer deposition (ALD) is a thin-film deposition technique based on the sequential use of a gas phase chemical process; it is a subclass of chemical vapour deposition. The majority of ALD reactions use two chemicals called precursors. These precursors react with the surface of a material one at a time in a sequential, self-limiting, manner. Through the repeated exposure to separate precursors, a thin film is slowly deposited. ALD is a key process in the fabrication of semiconductor devices, and part of the set of tools available for the synthesis of nanomaterials.

Disilane is a chemical compound with chemical formula Si2H6 that was identified in 1902 by Henri Moissan and Samuel Smiles (1877–1953). Moissan and Smiles reported disilane as being among the products formed by the action of dilute acids on metal silicides. Although these reactions had been previously investigated by Friedrich Woehler and Heinrich Buff between 1857 and 1858, Moissan and Smiles were the first to explicitly identify disilane. They referred to disilane as silicoethane. Higher members of the homologous series SinH2n+2 formed in these reactions were subsequently identified by Carl Somiesky (sometimes spelled "Karl Somieski") and Alfred Stock.

Sputter deposition physical vapor deposition (PVD) method of thin film deposition by sputtering

Sputter deposition is a physical vapor deposition (PVD) method of thin film deposition by sputtering. This involves ejecting material from a "target" that is a source onto a "substrate" such as a silicon wafer. Resputtering is re-emission of the deposited material during the deposition process by ion or atom bombardment. Sputtered atoms ejected from the target have a wide energy distribution, typically up to tens of eV. The sputtered ions can ballistically fly from the target in straight lines and impact energetically on the substrates or vacuum chamber. Alternatively, at higher gas pressures, the ions collide with the gas atoms that act as a moderator and move diffusively, reaching the substrates or vacuum chamber wall and condensing after undergoing a random walk. The entire range from high-energy ballistic impact to low-energy thermalized motion is accessible by changing the background gas pressure. The sputtering gas is often an inert gas such as argon. For efficient momentum transfer, the atomic weight of the sputtering gas should be close to the atomic weight of the target, so for sputtering light elements neon is preferable, while for heavy elements krypton or xenon are used. Reactive gases can also be used to sputter compounds. The compound can be formed on the target surface, in-flight or on the substrate depending on the process parameters. The availability of many parameters that control sputter deposition make it a complex process, but also allow experts a large degree of control over the growth and microstructure of the film.

Chemical vapour infiltration (CVI) is a ceramic engineering process whereby matrix material is infiltrated into fibrous preforms by the use of reactive gases at elevated temperature to form fiber-reinforced composites. The earliest use of CVI was the infiltration of fibrous alumina with chromium carbide. CVI can be applied to the production of carbon-carbon composites and ceramic matrix composites. A similar technique is chemical vapour deposition (CVD), the main difference being that the deposition process of CVD is on hot bulk surfaces, while the deposition process of CVI is on porous substrates.

Vapor–liquid–solid method

The vapor–liquid–solid method (VLS) is a mechanism for the growth of one-dimensional structures, such as nanowires, from chemical vapor deposition. The growth of a crystal through direct adsorption of a gas phase on to a solid surface is generally very slow. The VLS mechanism circumvents this by introducing a catalytic liquid alloy phase which can rapidly adsorb a vapor to supersaturation levels, and from which crystal growth can subsequently occur from nucleated seeds at the liquid–solid interface. The physical characteristics of nanowires grown in this manner depend, in a controllable way, upon the size and physical properties of the liquid alloy.

Copper indium gallium selenide solar cells direct bandgap semiconductor useful for the manufacture of solar cells

A copper indium gallium selenide solar cell is a thin-film solar cell used to convert sunlight into electric power. It is manufactured by depositing a thin layer of copper, indium, gallium and selenium on glass or plastic backing, along with electrodes on the front and back to collect current. Because the material has a high absorption coefficient and strongly absorbs sunlight, a much thinner film is required than of other semiconductor materials.

Combustion chemical vapor deposition (CCVD) is a chemical process by which thin-film coatings are deposited onto substrates in the open atmosphere.

Eutectic bonding

Eutectic bonding, also referred to as eutectic soldering, describes a wafer bonding technique with an intermediate metal layer that can produce a eutectic system. Those eutectic metals are alloys that transform directly from solid to liquid state, or vice versa from liquid to solid state, at a specific composition and temperature without passing a two-phase equilibrium, i.e. liquid and solid state. The fact that the eutectic temperature can be much lower than the melting temperature of the two or more pure elements can be important in eutectic bonding.

Trimethylsilane or trimethylsilyl hydride, is a gas at ambient conditions with the formula C3H10Si. It is very flammable. Trimethylsilane is used in the semi-conductor industry as precursor to deposit dielectrics and barrier layers via plasma-enhanced chemical vapor deposition (PE-CVD).. It is also used a source gas to deposit TiSiCN hard coatings via plasma-enhanced magnetron sputtering (PEMS). It has also been used to deposit silicon carbide hard coatings via low-pressure chemical vapor deposition (LP-CVD) at relatively low temperatures <1000oC. It is an expensive gas but safer to use than silane (SiH4); and produces properties in the coatings that cannot be undertaken by multiple source gases containing silicon and carbon.

A rapidly increasing list of graphene production techniques have been developed to enable graphene's use in commercial applications.

Two dimensional hexagonal boron nitride is a material of comparable structure to graphene with potential applications in e.g. photonics., fuel cells and as a substrate for two-dimensional heterostructures. 2D h-BN is isostructural to graphene, but where graphene is conductive, 2D h-BN is a wide-gap insulator.

Low-energy plasma-enhanced chemical vapor deposition

Low-Energy Plasma-Enhanced Chemical Vapor Deposition (LEPECVD) is a plasma-enhanced chemical vapor deposition technique used for the epitaxial deposition of thin semiconductor films. A remote low energy, high density DC argon plasma is employed to efficiently decompose the gas phase precursors while leaving the epitaxial layer undamaged, resulting in high quality epilayers and high deposition rates.

References

  1. "Low Pressure Chemical Vapor Deposition – Technology and Equipment". Crystec Technology Trading GmbH.
  2. Crystec Technology Trading GmbH, Plasma Enhanced Chemical Vapor Deposition – Technology and Equipment
  3. Tavares, Jason; Swanson, E.J.; Coulombe, S. (2008). "Plasma Synthesis of Coated Metal Nanoparticles with Surface Properties Tailored for Dispersion". Plasma Processes and Polymers. 5 (8): 759. doi:10.1002/ppap.200800074.
  4. Schropp, R.E.I.; B. Stannowski; A.M. Brockhoff; P.A.T.T. van Veenendaal; J.K. Rath. "Hot wire CVD of heterogeneous and polycrystalline silicon semiconducting thin films for application in thin film transistors and solar cells" (PDF). Materials Physics and Mechanics. pp. 73–82.
  5. Gleason, Karen K.; Kenneth K.S. Lau; Jeffrey A. Caulfield (2000). "Structure and Morphology of Fluorocarbon Films Grown by Hot Filament Chemical Vapor Deposition". Chemistry of Materials. 12 (10): 3032. doi:10.1021/cm000499w.
  6. Dorval Dion, C.A.; Tavares, J.R. (2013). "Photo-Initiated Chemical Vapour Deposition as a Scalable Particle Functionalization Technology (A Practical Review)". Powder Technology. 239: 484–491. doi:10.1016/j.powtec.2013.02.024.
  7. Wahl, Georg et al. (2000) "Thin Films" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. doi : 10.1002/14356007.a26_681
  8. Gleason, Karen; Ayse Asatekin; Miles C. Barr; Samaan H. Baxamusa; Kenneth K.S. Lau; Wyatt Tenhaeff; Jingjing Xu (May 2010). "Designing polymer surfaces via vapor deposition". Materials Today. 13 (5): 26–33. doi:10.1016/S1369-7021(10)70081-X.
  9. Stassen, I; Styles, M; Grenci, G; Van Gorp, H; Vanderlinden, W; De Feyter, S; Falcaro, P; De Vos, D; Vereecken, P; Ameloot, R (2015). "Chemical vapour deposition of zeolitic imidazolate framework thin films". Nature Materials . 15 (3): 304–10. Bibcode:2016NatMa..15..304S. doi:10.1038/nmat4509. PMID   26657328.
  10. Servi, Amelia T.; Guillen-Burrieza, Elena; Warsinger, David M.; Livernois, William; Notarangelo, Katie; Kharraz, Jehad; Lienhard V, John H.; Arafat, Hassan A.; Gleason, Karen K. (2017). "The effects of iCVD film thickness and conformality on the permeability and wetting of MD membranes". Journal of Membrane Science. 523: 470–479. doi:10.1016/j.memsci.2016.10.008. hdl:1721.1/108260. ISSN   0376-7388.
  11. Simmler, W., "Silicon Compounds, Inorganic", Ullmann's Encyclopedia of Industrial Chemistry , Weinheim: Wiley-VCH, doi:10.1002/14356007.a24_001
  12. Proceedings of the Third World Congress of Chemical Engineering, Tokyo, p. 290 (1986)
  13. Cao, Guozhong; Wang, Ying (2011). Nanostructures and Nanomaterials -- Synthesis, Properties and Applications. World Scientific Publishing. p. 248. doi:10.1142/7885. ISBN   978-981-4322-50-8.
  14. Sze, S.M. (2008). Semiconductor devices: physics and technology. Wiley-India. p. 384. ISBN   978-81-265-1681-0.
  15. Maruyama, Toshiro (1994). "Electrochromic Properties of Niobium Oxide Thin Films Prepared by Chemical Vapor Deposition". Journal of the Electrochemical Society. 141 (10): 2868. doi:10.1149/1.2059247.
  16. Rahtu, Antti (2002). Atomic Layer Deposition of High Permittivity Oxides: Film Growth and In Situ Studies (Thesis). University of Helsinki. hdl:10138/21065. ISBN   952-10-0646-3.
  17. 1 2 3 4 5 6 7 Liu, Zhuchen; Tu, Zhiqiang; Li, Yongfeng; Yang, Fan; Han, Shuang; Yang, Wang; Zhang, Liqiang; Wang, Gang; Xu, Chunming (2014-05-01). "Synthesis of three-dimensional graphene from petroleum asphalt by chemical vapor deposition". Materials Letters. 122: 285–288. doi:10.1016/j.matlet.2014.02.077.
  18. Park, Hye Jin; Meyer, Jannik; Roth, Siegmar; Skákalová, Viera (Spring 2010). "Growth and properties of few-layer graphene prepared by chemical vapor deposition". Carbon. 48 (4): 1088–1094. arXiv: 0910.5841 . doi:10.1016/j.carbon.2009.11.030. ISSN   0008-6223.
  19. Wei, Dacheng; Lu, Yunhao; Han, Cheng; Niu, Tianchao; Chen, Wei; Wee, Andrew Thye Shen (2013-10-31). "Critical Crystal Growth of Graphene on Dielectric Substrates at Low Temperature for Electronic Devices". Angewandte Chemie. 125 (52): 14371–14376. doi:10.1002/ange.201306086. ISSN   0044-8249.
  20. Chen, Jianyi; Guo, Yunlong; Wen, Yugeng; Huang, Liping; Xue, Yunzhou; Geng, Dechao; Wu, Bin; Luo, Birong; Yu, Gui (2013-02-14). "Graphene: Two-Stage Metal-Catalyst-Free Growth of High-Quality Polycrystalline Graphene Films on Silicon Nitride Substrates (Adv. Mater. 7/2013)". Advanced Materials. 25 (7): 992–997. doi:10.1002/adma.201370040. ISSN   0935-9648.
  21. 1 2 3 4 5 6 7 Patel, Rajen B.; Yu, Chi; Chou, Tsengming; Iqbal, Zafar (2014). "Novel synthesis route to graphene using iron nanoparticles". Journal of Materials Research. 29 (14): 1522–1527. Bibcode:2014JMatR..29.1522P. doi:10.1557/jmr.2014.165.
  22. 1 2 3 4 5 6 Murakami, Katsuhisa; Tanaka, Shunsuke; Hirukawa, Ayaka; Hiyama, Takaki; Kuwajima, Tomoya; Kano, Emi; Takeguchi, Masaki; Fujita, Jun-ichi (2015). "Direct synthesis of large area graphene on insulating substrate by gallium vapor-assisted chemical vapor deposition". Applied Physics Letters. 106 (9): 093112. Bibcode:2015ApPhL.106i3112M. doi:10.1063/1.4914114.
  23. Tang, Shujie; Wang, Haomin; Wang, Huishan (2015). "Silane-catalysed fast growth of large single-crystalline graphene on hexagonal boron nitride". Nature Communications. 6: 6499. arXiv: 1503.02806 . Bibcode:2015NatCo...6.6499T. doi:10.1038/ncomms7499. PMC   4382696 . PMID   25757864.
  24. 1 2 3 4 5 6 Zhang, CanKun; Lin, WeiYi; Zhao, ZhiJuan; Zhuang, PingPing; Zhan, LinJie; Zhou, YingHui; Cai, WeiWei (2015-09-05). "CVD synthesis of nitrogen-doped graphene using urea". Science China Physics, Mechanics & Astronomy. 58 (10): 107801. Bibcode:2015SCPMA..58.7801Z. doi:10.1007/s11433-015-5717-0.
  25. 1 2 3 4 5 6 Kim, Sang-Min; Kim, Jae-Hyun; Kim, Kwang-Seop; Hwangbo, Yun; Yoon, Jong-Hyuk; Lee, Eun-Kyu; Ryu, Jaechul; Lee, Hak-Joo; Cho, Seungmin (2014). "Synthesis of CVD-graphene on rapidly heated copper foils". Nanoscale. 6 (9): 4728–34. Bibcode:2014Nanos...6.4728K. doi:10.1039/c3nr06434d. PMID   24658264.
  26. Das, Shantanu; Drucker, Jeff (2017). "Nucleation and growth of single layer graphene on electrodeposited Cu by cold wall chemical vapor deposition". Nanotechnology. 28 (10): 105601. Bibcode:2017Nanot..28j5601D. doi:10.1088/1361-6528/aa593b. PMID   28084218.
  27. Das, Shantanu; Drucker, Jeff (28 May 2018). "Pre-coalescence scaling of graphene island sizes". Journal of Applied Physics. 123 (20): 205306. Bibcode:2018JAP...123t5306D. doi:10.1063/1.5021341.
  28. 1 2 Costello, M; Tossell, D; Reece, D; Brierley, C; Savage, J (1994). "Diamond protective coatings for optical components". Diamond and Related Materials. 3 (8): 1137–1141. Bibcode:1994DRM.....3.1137C. doi:10.1016/0925-9635(94)90108-2.
  29. Sun Lee, Woong; Yu, Jin (2005). "Comparative study of thermally conductive fillers in underfill for the electronic components". Diamond and Related Materials. 14 (10): 1647–1653. Bibcode:2005DRM....14.1647S. doi:10.1016/j.diamond.2005.05.008.
  30. Isberg, J (2004). "Single crystal diamond for electronic applications". Diamond and Related Materials. 13 (2): 320–324. Bibcode:2004DRM....13..320I. doi:10.1016/j.diamond.2003.10.017.
  31. Krauss, A (2001). "Ultrananocrystalline diamond thin films for MEMS and moving mechanical assembly devices". Diamond and Related Materials. 10 (11): 1952–1961. Bibcode:2001DRM....10.1952K. doi:10.1016/S0925-9635(01)00385-5.

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