thin film deposition

Easy read Thin Film Deposition and its types in 2021

Know in detail about the thin film deposition its various types and applications

Thin Film Deposition

The action of applying a thin film to a surface is known as a thin-film deposition. Thin-film deposition is any procedure for depositing a thin film of material onto a substrate or onto formerly deposited layers. “Thin” is a relative word, but most deposition procedures allow layer thickness to be structured within a few tens of nanometers, and molecular beam epitaxy allows single layers of atoms to be deposited at a time.

It is useful in the production of optics (for reflective or anti-reflective coatings, for instance), packaging (Aluminium-coated PET film), electronics (layers of insulators, semiconductors, and conductors form integrated circuits), and in contemporary art. Similar processes are sometimes used where the thickness is not essential, for example, the deposition of silicon and supplemented uranium by a CVD-like process after gas-phase processing and the refinement of copper by electroplating.

thin film deposition
Thin Film Deposition. Thanks intechopen.com

Deposition procedures fall into two broad classes, depending on whether the process is primarily chemical or physical.

Chemical Deposition

Here, a fluid precursor undergoes a chemical transformation at a solid surface, leaving a solid layer. An everyday example is the development of soot on an object when it is placed inside a flare. Since the fluid surrounds the solid thing, deposition ensues on every exterior, with little regard to direction; thin films from chemical deposition procedures tend to be conformal, rather than directional. 

Types of Chemical Deposition

Chemical solution deposition (CSD) aids a liquid precursor. Usually, a solution of organometallic powders liquified in an organic solvent. Plating depends on liquid precursors, often a solution of water with a salt of the metal to be deposited. Some plating processes are impelled entirely by reagents in the solution (usually for noble metals). However, by far, the most commercially important method is electroplating.

It was not generally used in semiconductor processing for many years but has seen a resurgence with the more widespread use of chemical-mechanical polishing procedures. This is a relatively economical, simple thin-film process that can produce stoichiometrically accurate crystalline phases.

Chemical vapour deposition (CVD) commonly employs a gas-phase precursor, habitually a hydride or halide of the element to be deposited. For instance, MOCVD, an organometallic gas, is utilised. Industrial procedures often use extremely low pressures of precursor gas.

Plasma enhanced CVD (PECVD) uses an ionised vapour, or plasma, as a precursor. Unlike the soot example above, commercial PECVD depends on electromagnetic potentials such as microwave excitation, electric current rather than a chemical reaction, to produce a plasma.

Plasma enhanced CVD. Thanks, https://www.researchgate.net/publication/270671650

Physical Deposition

Physical deposition uses mechanical or thermodynamic means to produce a thin film of solid. An everyday instance is the formation of frost. Since most engineering resources are held together by relatively high energies, and chemical reactions are not used to store these energies. Commercial physical deposition methods tend to require a low-pressure vapour background to function properly; most can be categorised as physical vapour deposition (PVD).

The material to be deposited is engaged in an active, entropic environment so that particles of material escape its surface. Facing this source is a chiller that draws energy from these particles as they arrive, allowing them to form a solid layer. The whole method is kept in a vacuum deposition chamber, to allow the particles to travel as spontaneously as possible. Meanwhile, particles tend to follow a straight path, films deposited by physical means are commonly directional, rather than conformal.

Types of Physical Deposition

A thermal evaporator employs an electric resistance heater to melt the substance and raise its vapour pressure to a suitable range. This is done in an elevated vacuum, and both let the vapour to arrive at the substrate without changing with or scattering against other gas-phase atoms in the chamber and reduce the amalgamation of scums from the residual gas in the vacuum chamber.

Only materials with a much-elevated vapour pressure than the heating element can be deposited without the contagion of the film. Molecular beam epitaxy is a particularly high-level form of thermal evaporation.

An electron beam evaporator bonfires a high-energy beam from an electron beam gun to boil a small spot of matter; since the heating is not uniform, lower vapour pressure materials can be deposited. The beam is customarily bent through an angle of 270° in order to confirm that the gun filament is not openly exposed to the evaporant flux—typical deposition rates for electron beam vaporisation array from 1 to 10 nanometers per second.

Electron Beam Evaporator. Thanks, https://www.researchgate.net/profile/Nilofar-Asim

Sputtering relies on a plasma – usually a noble gas, such as argon to knock material from an ” aim at ” a few atoms at a period. A process used to deposit thin films of an object onto a substrate. By initiating a gaseous plasma and then quickening the ions from this plasma into some source material (target), the source material is eroded by the arriving ions via energy transfer. It is ejected in the form of neutral particles – either single atoms or clusters of molecules.

As these neutral particles are ejected, they will travel in a straight line unless they come into contact with other particles or a near-surface. The target kept at a comparatively low temperature. Subsequently, the process is not one of evaporation, assembling this as one of the most malleable deposition procedures. It is especially useful for compounds, where different constituents would otherwise tend to evaporate at different rates.

Sputtering
Sputtering

Pulsed laser deposition techniques work by an ablation process. Pulses of focused laser light turn vapour the surface of the target substance and convert it to plasma; this plasma usually regresses to a gas before it reaches the substrate.

Pulse Laser Deposition. Thanks, https://groups.ist.utl.pt/

Cathodic arc deposition (arc-PVD) is a type of ion beam deposition where an electrical arc is created that blasts ions from the cathode. The arc has a remarkably high power density resulting in a high level of ionisation (30-100%), multiply charged ions, neutral particles, clusters, and droplets. If a reactive gas is commenced during the evaporation process, dissociation, ionisation, and excitation can occur during contact with the ion flux and a compound film will be deposited.

Cathodic Arc Deposition. Thanks, https://www.advancedenergyblog.com/

Now that you have read about Thin Film Deposition. Check out our course on Ampersand Academy Read this interesting article about Sol Gel Technique.

Sol Gel Technique

Easy read on Sol gel Technique in 2021

Know in detail about the technique sol gel technique and its advantages

Sol gel method is a type of chemical solution deposition technique or a wet chemical route for the synthesis of colloidal dispersions of oxides – altered to powders, fibres, thin-film sand monoliths. Sol-gel coating is a process of preparation of single or multi-component oxide coating which may be glass, ceramic or crystalline ceramic depending on the process. Also, the nanomaterials used in modern ceramic and device technology require high purity and facilitate control over composition and structure.

The sol-gel method used recently in the fields of materials science and ceramic engineering and these methods is used primarily for the fabrication of materials (typically a metal oxide) starting from a chemical solution which acts as the precursor for an integrated network (or gel) of either discrete particles or network polymers. Typical precursors are metal alkoxides and metal chlorides, which undergo various forms of hydrolysis and polycondensation reactions.

The formation of a metal oxide involves connecting the metal centres with oxo (M-O-M) or hydroxo (M-OH-M) bridges, therefore generating metal-oxo or metal-hydroxo polymers in solution. Thus, the sol evolves towards the formation of a gel-like diphasic system containing both a liquid phase and solid phase whose morphologies range from discrete particles to continuous polymer networks.

Sol Gel Technique
Sol Gel Technique. Thanks, Wikipedia

The precursor sol can be either deposited on a substrate to form a film, cast into a suitable container with the desired shape, or used to synthesize powders. The sol-gel approach is a cheap and low-temperature technique that allows for excellent control of the product’s chemical composition. Even small quantities of dopants, such as organic dyes and rare earth elements, can be introduced in the sol and end up uniformly dispersed in the final product.

It is used in ceramic processing and manufacturing as an investment casting material, or as a means of producing very thin films of metal oxides for various purposes. Sol-gel derived materials have diverse applications in optics, electronics, energy, space, biosensors, medicine, reactive material and separation technology.

Advantages of Sol-gel Technique

The sol-gel coating is one of the interesting methods because it has many advantages. Examples are as the followings

  • The chemical reactants for the sol-gel process can be conveniently purified by distillation and crystallization.
  • All starting materials are mixed at the molecular level in the solution so that a  high degree of homogeneity of films can be expected.
  • The trace elements in the form of organometallic compounds or soluble organic or inorganic salts can be added to adjust the microstructure or to improve the structural, optical, and electrical properties of oxide films.
  • The viscosity, surface tension and concentration of a solution can be easily adjusted.
  • Large area films of desired composition and thickness can be formed on a complex geometry substrate.
  • It facilitates to the formation of films of complex oxides and eases to control the composition and microstructure of the deposited films.
  • Sol-gel coating is exclusively applied for the fabrication of transparent layers with a high degree of planarity and surface quality.

Now that you have read about Sol Gel Technique. Check out our course on Ampersand Academy Read this interesting article about Thin Film Deposition.