Deposition

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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.

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 Primarily Used for:
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
Sputter deposition 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
CVD Parylene Deposition Parylene ~30-50Å/sec 20ºC Good Sidewall coverage Good Very Low Good unknown Thick (0.8-75μm) encapsulation ("body safe") and insulation with parylene
Plasma Enhanced CVD (PECVD) Mainly Dielectrics 5-200Å/sec 200-400ºC Some sidewall coverage Good Very Low Good 10-100nm Lower temp oxide/nitride deposition
Low Pressure CVD (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
Thermal oxidation Oxide on Silicon 0.1-100 Å/sec 900-1200ºC Isotropic - very good sidewall coverage Very Good Very Low Very Good 1-10nm Best quality oxide dep where substrate can handle higher temp and slower dep rate
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
Atomic Layer Deposition (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


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.

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. === Low Pressure Chemical Vapor Deposition (LPCVD)

Parylene deposition

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 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.

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)