Deposition

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), 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:
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
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
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

Atomic layer deposition (ALD)

Main article: Atomic layer deposition

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)

Main article: Chemical vapor deposition

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.

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)

Main article: Physical vapor deposition

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

• Thermal oxidation
• Carbon nanotube 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.

Refractive index

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.

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.

Further reading

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