Deposition or Growth refers to the controlled synthesis, growth or transfer of materials as thin films on a substrate. A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometers in thickness.
Typical technologies include atomic layer deposition (ALD), chemical vapor deposition (CVD), electrodeposition/ electroplating or electrochemical deposition (ECD), and physical vapor deposition (PVD) molecular beam epitaxy (MBE). Selection of deposition technique depends on material deposited, desired film characteristics and substrate temperature tolerance:
|Deposition Method||Materials||Deposition Rate||Substrate Temperature||Confomality||Film Density||Impurity Levels||Uniformity||Grain Size||Primarily Used for:|
|Thermal Evaporation||Low Melting Point metals and materials||1-10 Å/sec||10-100ºC||Highly directional - no sidewall coverage||Poor||High||Poor||10-100nm||Liftoff metal deposition especially e-beam resists|
|E-beam Evaporation||Metals and Dielectrics||1-15 Å/sec||10-100ºC||Highly directional - no sidewall coverage||Poor||Low||Poor||10-100nm||Liftoff or thicker metal deposition|
|Sputtering||Metals and dielectrics||0.1-10 Å/sec||50-300ºC||Some sidewall coverage||Good||Low||Good||~10nm||More conformal metal and dielectric thin film deposition. Compounds that do not evaporate while keeping stoichiomettry|
|PECVD||Mainly Dielectrics||5-200Å/sec||200-400ºC||Some sidewall coverage||Good||Very Low||Good||10-100nm||Lower temp oxide/nitride deposition|
|LPCVD||Mainly Dielectrics||10-100 Å/sec||600-1200ºC||Isotropic - good sidewall coverage||Very Good||Very Low||Very Good||1-10nm||Better quality oxide/nitride dep where substrate can handle higher temp|
|ECD/Plating||Conductive Materials||Depends on process||0-100ºC||Isotropic - good sidewall coverage||Good||Depends on process||Depends on process||Depends on Process||Thicker films deposition with good conformality|
|ALD||Metals, metal oxides and nitrides||~1Å/ cycle.
5-200 sec cycle
|50-300ºC||Isotropic - very good sidewall coverage||Good||Low||Very good||10-100nm||Very thin, very conformal films such as gate dieletrics, barriers, encapsualtion|
Atomic layer deposition (ALD)
Atomic Layer Deposition (ALD) is a technique which allows the deposition of ultra-thin films, a few nanometers thick, highly conformal and self limiting to be deposited in a precisely controlled way. These characteristics offer many benefits in semiconductor engineering, MEMS, catalysis and other nanotechnology applications. In ALD the precursor gas or gases are introduced, one at time, into the reactor and made react with the surface until all reactive sites are occupied and the reaction stops. The precursor gases are pulsed, alternatively, never present simultaneously in the chamber. These type of deposition is slow and requires highly pure substrates to obtained the desired films.
Chemical vapor deposition (CVD)
Chemical vapor deposition (CVD) consists of the substrate being exposed to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired deposit. There are many methods for enhancing the chemical reaction rates of the precursors. The LNF has fourteen Low Pressure CVD (LPCVD) furnace tubes and five Plasma Enhanced CVD (PECVD) chambers.
Electrodeposition/ Electroplating/ Electrochemical deposition (ECD)
Electrodeposition, which is only available on conductive substrates and for conductive films, is the technique recommended when metal layers of more than a micron of thickness are needed. It is also the technique of choice when there is no line of site with the surface to be deposited, for example the filling of vias in the semiconductor processing. The principle is simple: positive ions are attracted to the negative electrode (anode which is the sample in the case of metal deposition) and negative ions travel towards the cathode or positive electrode. ECD is an electrochemical cell, which consists of a cathode, anode, and electrolyte that contains the ion to be deposited. Electrodeposition does not require vacuum environment, thus making it relatively inexpensive and it can be done in batch or continue processes. It creates thick, durable film which surface finish can be tailored depending on the requirements.
Physical vapor deposition (PVD)
Physical vapor deposition (PVD) describes a variety of vacuum deposition methods used to deposit thin films by the condensation of a vaporized form of the desired film material onto various substrates.
This section requires expansion.
Figures of merit
Deposition rate, usually expressed in Å/sec, is measured at the substrate using various methods depending on the type of film deposited. It is measured real-time in the evaporators and after run completion for other techniques.
Defines optical properties of a given material for a specific frequency or wavelength of light. Also known as index of refraction n. The index of the film is measured using Ellipsometry that also gives clues to the density, dielectric constant, and stoichiometry of the film .
Conformality or Step Coverage
Step coverage is the measure of how much coating is on the bottom/sidewall of a feature vs how much coating is on the top/field areas. It is highly dependent on the geometry of the features and the type of deposition chosen. ALD, TEOS, HTO, and Thermal oxide are very conformal. LTO, PECVD, Sputtering, and Evaporation are much less conformal.
The elastic mismatch between the thin film deposited and the substrate that results in a change in substrate curvature. Residual stress is typically defined by a unit of measurement (MPa) across a given area.
This section requires expansion.
- Handbook of Thin Film Deposition: Processes and Technologies
- Other stuff, e.g. technology workshop slides
- External links (can be in another section below, if appropriate)