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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. Based on the growth dynamics which prevail during the deposition, the resulting material can be amorphous, polycrystalline, or crystalline. Deposition techniques which result in crystalline material are often referred to as epitaxial growth.

Contents

Technologies

Typical technologies include atomic layer deposition (ALD), chemical vapor deposition (CVD), electrodeposition/ electroplating or electrochemical deposition (ECD), physical vapor deposition (PVD), and 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 Primary use
Evaporation Metals and dielectrics 1–15 Å/sec 10–100ºC No sidewall coverage Poor Low Poor 10–100 nm lift-off patterning
Sputter deposition Metals and dielectrics 0.1–10 Å/sec 50–300ºC Some sidewall coverage Good Low Good ~10 nm Conformal metal and dielectric thin films. Better stoichiometry than evaporation
CVD Parylene deposition Parylene ~30–50 Å/sec 20ºC Good sidewall coverage Good Very low Good Unknown Thick (0.8–75μm) encapsulation and insulation
Biocompatible
Plasma Enhanced CVD (PECVD) Dielectrics 5–200 Å/sec 200–400ºC Some sidewall coverage Good Very low Good 10–100 nm Lower temperature oxide/nitride deposition
Low pressure CVD (LPCVD) Mainly Dielectrics 10–100 Å/sec 600–1200ºC Good sidewall coverage Very good Very low Very good 1–10 nm Better quality oxide/nitride dep where substrate can handle higher temp
Thermal oxidation Oxide on silicon 0.1–100 Å/sec 900–1200ºC Very good sidewall coverage Very good Very low Very good 1–10 nm Best quality oxide when substrate can handle higher temp and slower dep rate
ECD/Plating Conductive Materials Depends on process 0–100 ºC Good sidewall coverage Good Depends on process Depends on process Depends on Process Thicker films deposition with good conformality
Atomic layer deposition (ALD) Metals, metal oxides and nitrides ~1 Å/cycle
5–200 sec cycle
50–300ºC Very good sidewall coverage Good Low Very good 10–100 nm Very thin, conformal films
gate dieletrics, barriers, encapsulation


Chemical vapor deposition (CVD)

In chemical vapor deposition (CVD), a substrate is typically heated and exposed to one or more gaseous precursors, which react and/or decompose on the substrate surface to produce the desired thin film material. CVD can be used to grow high quality, uniform thin films of various materials, such as silicon dioxide, silicon nitride, and many others. CVD can be subdivided into classifications based on pressure requirements (atmospheric (APCVD), low-pressure (LPCVD), and ultra-high vacuum (UHCVD)). It can also be classified based on the mechanism used to decompose the source gas: plasma-enhanced CVD (PECVD) breaks apart gas molecules by application of ionizing voltage, whereas LPCVD and APCVD use elevated temperatures to cause the source gas to decompose.


Electroplating

Main article: Electroplating

Electroplating (electrodeposition, electrochemical deposition) is the technique recommended when metal layers of more than a micron of thickness are needed. It is only available on conductive substrates and for conductive films. It is also the technique of choice when there is no line of sight with the surface to be deposited, for example the filling of vias in 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 a vacuum environment and can be done in batch processes, thus making it relatively inexpensive. It creates thick, durable film whose 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.

Growth

Figures of merit

Deposition rate

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.

Film Composition

Also known as stoichiometry. Usually expressed in units of atomic % or weight %. Film composition affects film behavior, optical constants, stress, etch rates, and other physical properties like melting point, vapor pressure, etc.

Refractive index

Defines optical properties of a given material for a specific frequency or wavelength of light. Also known as index of refraction, or n. The refractive index of a film can be measured using Ellipsometry and also gives clues as to the density, dielectric constant, and stoichiometry of the film [1].

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.

Film Stress

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.

Thermal budget

References

  1. Handbook of Thin Film Deposition: Processes and Technologies

Further reading

  • Other stuff, e.g. technology workshop slides
  • External links (can be in another section below, if appropriate)