PVD refers to a set of low temperature processes that involve the condensation of vaporized solid material on top of the surface of the solid material under a partial vacuum condition.
Sputtering is a PVD process where a plasma-heated cathode is bombarded with argon ions.
The 'carrier gas' in CVD is the gas that carries the reactants over the hot substrate surface.
The results of the CVD process include coatings, powders, fibers, monoliths, and composites.
High purity and conformal films, high deposition rates, and relatively low vacuum requirements.
Arc Evaporation is a process where an arc with a diameter of just a few microns is run over the solid source material, causing it to evaporate. The high currents and power densities used result in the evaporated source material being almost totally ionized, forming a high-energy plasma. The metal ions combine with the reactive gas introduced into the chamber and strike the tools or components to be coated with high energy, depositing as a thin and highly adherent coating.
Thin films offer benefits such as conservation of scarce materials, production of nanostructured coatings and nanocomposites, ecological considerations (reduction of effluent output and power consumption), improved functionality of existing products, solutions to previously unsolved engineering problems, and the creation of entirely new and revolutionary products.
Applications of PVD include decorative coatings on plastic and metal parts, antireflection coatings on optical lenses, depositing metal for electrical connections in integrated circuits, and coating titanium nitride onto cutting tools and plastic injection molds for wear resistance.
Ion plating is a PVD process that uses reactive electron beam evaporation to deposit coatings.
The output variables in the CVD process include the carbon deposit amount (C%) and the average diameter of carbon nanotubes (D).
PECVD stands for Plasma-enhanced Chemical Vapor Deposition, a type of CVD process used in microfabrication.
The substrate loading system in a CVD apparatus allows for the placement and removal of substrates onto which the thin films will be deposited.
Materials for CVD may include metals such as Al, Ag, Au, W, Cu, Pt, and Sn, as well as organic materials like Al2O3, polysilicon, SiO2, Si3N4, piezoelectric ZnO, and SMA TiNi.
Arc Evaporation is a PVD process where a high power travelling arc vaporizes the source material.
Epitaxy is needed to produce a buried layer in bipolar transistors.
A family of processes in which a solid material is converted to its vapor phase in a vacuum chamber and condensed onto a substrate surface as a very thin film.
Solar cells can be manufactured using chemical vapor deposition techniques.
LPCVD operates at pressures of 1-8 Torr and temperatures of 550-900°C, with deposition rates of 50-180 (10^-10 m/min) for SiO2, 30-80 for Si3N4, and 100-200 for polysilicon.
Sputtering involves the bombardment of the cathodic coating material with argon ions, causing the surface atoms to escape and then be deposited onto a substrate. It can be applied to nearly any material but has a slow deposition rate.
Vacuum Evaporation is a PVD process where the source material is heated to form vapor.
Thin film technology can modify and tune surface properties to meet application-specific demands for better performance.
In CMOS structures, epitaxy is used to create layers of different doping.
The sputtering process is carried out with plasmas under very low pressure in high vacuum up to 5x10^-7 torr and at room temperature.
While sputtering uses bombardment with argon ions to remove coating material from a metal plate, ion plating evaporates the metallic component of the coating material using a low-voltage arc.
Precursors need to be volatile, precursors can be toxic and costly, high temperature restricts substrate material, and stress in films with different thermal expansion.
The exhaust system in a CVD apparatus removes the by-products and unreacted gases from the reactor chamber to maintain a clean environment for the deposition process.
Decreasing the pressure of the gas, P, is expected to enhance the rate, r, of the CVD process, making LPCVD a popular choice in microfabrication.
Merits of APCVD include simplicity, high deposition rate, and low temperature. Demerits include poor step coverage and particle contamination.
Thin films can range from single crystal to amorphous, fully dense to less than fully dense, pure to impure, and thin to thick.
Epitaxy refers to the deposition of a crystalline overlayer on a crystalline substrate, where there is registry between the overlayer and the substrate.
CVD involves the flow of a gas containing diffused reactants (normally in vapor form) over the hot substrate surface. The gas that carries the reactants is called 'carrier gas'. The energy supplied by the surface temperature provokes chemical reactions of the reactants that form films during and after the reactions. The by-products of the chemical reactions are then let to the vent.
Inert Argon gas is used as the carrier gas for metal vapor in the sputtering process.
Pressure controls the thickness of the boundary layer and the degree of diffusion in the CVD process.
APCVD stands for Atmospheric-pressure Chemical Vapor Deposition, a type of CVD process used in microfabrication.
CVD processes usually take place at elevated temperatures and in vacuum in high class clean rooms.
Epitaxial growth is useful for applications that place stringent demands on a deposited layer, such as high purity, low defect density, abrupt interfaces, controlled doping profiles, high repeatability and uniformity, and safe, efficient operation.
Chemical Vapor Deposition (CVD) is used extensively for producing thin films by depositing various foreign materials over the surface of silicon substrates or over other thin films already deposited on the silicon substrate.
Vacuum Evaporation, Arc Evaporation, Sputtering, Ion Plating.
Resistance Heating and Electron Beam Evaporation.
The vacuum system in a CVD apparatus maintains a controlled low-pressure environment, which is essential for the proper flow and reaction of precursor gases during the deposition process.
PECVD stands for Plasma Enhanced Chemical Vapor Deposition, a method that uses plasmas generated from high energy RF (radio-frequency) sources to deposit thin films at lower substrate temperatures.
LPCVD is used for depositing doped and undoped oxides, silicon, nitride, polysilicon, and tungsten.
The epitaxy process is similar to CVD as it uses a carrier gas with reactants that release the same material as the substrates in homoepitaxy.
Thin films are made by Chemical Vapor Deposition (CVD), Physical Vapor Deposition (PVD), and Epitaxy methods.
Ion Plating is a PVD process where evaporation is achieved by a low voltage arc.
The properties of the CVD process mechanism include being a vapor-transfer process and involving atomistic and molecular level chemical reactions.
Higher temperatures (900–1,200 °C) favor the growth of single-walled carbon nanotubes (SWNTs), while lower temperatures (600–900°C) yield multi-walled carbon nanotubes (MWNTs).
A typical CVD cycle involves multiple steps with specific times, temperatures, and gas flow rates, such as ramping to different temperatures and maintaining specific gas flow rates for each step.
It is applicable to an almost unlimited combination of coatings and substrate materials.
Refractory metals are used on jet engine turbine blades for their high resistance to heat and wear.
Merits of LPCVD include excellent purity and uniformity, and large wafer capacity. Demerits include high temperature and low deposition rates.
Molecular Beam Epitaxy (MBE) relies on the sublimation of ultrapure elements, which then condense on a wafer in a vacuum chamber with a pressure of approximately 10^-11 Torr. The 'beam' refers to molecules that do not collide with either the chamber walls or existing gas atoms, and the growth rate is about 1 μm/hr.
The typical chemical reaction for dichlorosilane (SiH2Cl2) in epitaxy is SiH2Cl2 → Si (solid) + H2 (gas) + Cl2 (gas).
Epitaxy is the extension of a single-crystal substrate by growing a film of the same single-crystal material. It refers to the deposition of a crystalline overlayer on a crystalline substrate, where there is registry between the overlayer and the substrate.
Chemical Vapor Deposition (CVD) may be defined as the deposition of a solid material from vapor phase on a heated surface during a chemical reaction.
Disadvantages of LPE include rough surfaces and poor thickness uniformity.
An engineered wafer is a clean, flat layer on top of a less ideal silicon (Si) substrate, often used on top of SOI structures, such as silicon on sapphire, to provide a higher purity layer on a lower quality substrate like SiC.
Sputtering is used to deposit thin metal films in the order of 100 Å (1 Å = 10^-10 m) onto the substrate surface.
Metal vapor is created by the plasma generated by high energy RF sources in the sputtering process.
LPCVD stands for Low-pressure Chemical Vapor Deposition, a CVD process that operates in vacuum at about 1 torr (1 mm Hg) and is popular in microfabrication.
An energy source in a CVD apparatus provides the necessary energy to activate the precursor gases, facilitating the chemical reactions required for thin film deposition.
CVD is used to deposit thin films of materials essential for the construction of integrated circuits.
Vapor Phase Epitaxy is a specific form of chemical vapor deposition (CVD) where reactants are introduced as gases. The material to be deposited is bound to ligands, which dissociate to allow the desired chemistry to reach the surface. While some desorption occurs, most adsorbed atoms find the proper crystallographic position.
The epitaxy deposition process is used to deposit polysilicon films on silicon substrate surfaces.
The term thin film is usually applied to surface deposition layers which are 2-dimensional and have the thickness range below 10 microns (10^-6 meters).
Evacuation of the chamber must precede the PVD process.
In III-V devices, interface quality is key for the performance of heterojunction bipolar transistors, LEDs, and lasers.
The input variables in the CVD process include preheating time (T preheat), reaction time (T react), temperature (T), pressure (P), and gas flow rate (F).
The gas delivery system in a CVD apparatus is responsible for supplying the precursor gases to the reactor chamber where the chemical vapor deposition process occurs.
Increasing the process temperature typically increases diffusivity, D, but it can harm the substrate.
CVD is used for applications requiring resistance to wear, corrosion, erosion, and thermal shock.
Polysilicons are doped pure silicon crystals that are randomly oriented and are used to conduct electricity at desired locations on silicon substrates.
CVD is a generic term for the deposition of thin films via a series of chemical reactions at high temperature. The constituent of the target in the vapor phase reacts via a chemical process near the surface or onto the surface of the substrate, leading to the growth of the thin film.
Vacuum evaporation involves heating the material to be deposited (the source) to evaporate it. Evaporated atoms leave the source and follow straight line paths until they collide with other gas molecules or strike the solid surface.
The 'diffused reactants' in CVD are foreign materials that need to be deposited on the substrate surface.
The reactor chamber in a CVD apparatus is the main area where the chemical reactions take place, leading to the deposition of thin films on the substrate.
The Mond process is used to reduce nickel from its ore.
APCVD is typically used for depositing doped and undoped oxides.
Merits of PECVD include lower substrate temperature, fast deposition, and good adhesion. Demerits include vulnerability to chemical contamination.
The normal process temperature for dichlorosilane (SiH2Cl2) is 1100°C, with a deposition rate of 0.1-0.8 μm/min.
1. Synthesis of coating vapor, 2. Vapor transport to substrate, 3. Condensation of vapors onto substrate surface.
LPE involves the precipitation of a crystalline film from a supersaturated melt onto a substrate. The temperature is increased until a phase transition occurs and then reduced for precipitation. By controlling cooling rates, the kinetics of layer growth can be controlled. It is a low-cost method for yielding films of controlled composition, thickness, and lower dislocation densities.
MBE involves the interaction of molecular or atomic beams on the surface of a heated crystalline substrate. Solid source materials sublimate, providing an angular distribution of atoms or molecules in a beam. The substrate is heated to the necessary temperature, and the gaseous elements condense on the wafer where they may react with each other. Atoms on a clean surface are free to move until finding the correct position in the crystal lattice to bond, with growth occurring at the step edges formed.
The two types of reactors used for epitaxy deposition are very similar to those used in CVD, but many of the carrier gases used are hydrogen (H2). For safety reasons, nitrogen (N2) gas is used to drive out any oxygen (O2) gas in the system before the process begins.
Gas flow rate, including precursor and inert gas flow rates, is crucial for controlling the deposition rate and uniformity of the thin film in the CVD process.
Metals, glass, and plastics.
Vapor-Phase Epitaxy (VPE) is a modified method of chemical vapor deposition (CVD) characterized by a growth rate of approximately 2 μm/min and the potential formation of undesired polycrystalline layers.
The normal process temperature for silicon tetrachloride (SiCl4) is 1225°C, with a deposition rate of 0.2-1.0 μm/min.
Metals, alloys, ceramics, other inorganic compounds, and some polymers.
Decreasing the velocity may enhance the rate, r, but it also results in a lower Reynolds number, increasing the boundary layer thickness, δ, which may cancel out the positive effect.
The two growth models for CNT synthesis in CVD are the tip-growth model and the base-growth model.
PECVD operates at pressures of 0.2-5 Torr and temperatures of 300-400°C, with deposition rates of 300-350 (10^-10 m/min) for Si3N4.
In Vapor Phase Epitaxy, silicon can be deposited by introducing SiCl4 with hydrogen, forming silicon and HCl gas. Alternatively, SiHCl3, SiH2Cl2, or SiH4 can be used, with SiH4 breaking down via thermal decomposition.
Materials such as GaAs can be deposited onto GaAs substrates using the epitaxy technique.
Coated carbide tools are used for resistance to wear, corrosion, erosion, and thermal shock.
Liquid-Phase Epitaxy (LPE) involves the formation of crystal layers from the melt existent on the substrate, with a growth rate ranging from 0.1 to 1 μm/min. It is challenging to produce thin films using this method.
The normal process temperature for trichlorosilane (SiHCl2) is 1175°C, with a deposition rate of 0.2-0.8 μm/min.
APCVD operates at pressures of 100-10 KPa and temperatures of 350-400°C, with normal deposition rates of 700 (10^-10 m/min) for SiO2.
The normal process temperature for silane (SiH4) is 1000°C, with a deposition rate of 0.1-0.5 μm/min.
PECVD is used for depositing low-temperature insulators over metals and for passivation.
The typical chemical reaction for silane (SiH4) in epitaxy is SiH4 → Si (solid) + 2H2 (gas).
Some methods of epitaxial deposition include Vapor-phase epitaxy (VPE), Molecular beam epitaxy (MBE), and Metal organic CVD (MOCVD).
