Difference between revisions of "Deposition"

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! style="font-weight: bold;" | Deposition Rate
 
! style="font-weight: bold;" | Deposition Rate
 
! style="font-weight: bold;" | Substrate Temperature
 
! style="font-weight: bold;" | Substrate Temperature
! style="font-weight: bold;" | Conformality
+
! style="font-weight: bold;" | Conformality/Sidewall Coverage
 
! style="font-weight: bold;" | Film Density
 
! style="font-weight: bold;" | Film Density
 
! style="font-weight: bold;" | Impurity Levels
 
! style="font-weight: bold;" | Impurity Levels
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| 1-15 Å/sec
 
| 1-15 Å/sec
 
| 10-100ºC
 
| 10-100ºC
| Highly directional - no sidewall coverage
+
| Poor-None
 
| Poor
 
| Poor
 
| Low
 
| Low
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| 0.1-10 Å/sec
 
| 0.1-10 Å/sec
 
| 50-300ºC
 
| 50-300ºC
| Some sidewall coverage
+
| OK
 
| Good
 
| Good
 
| Low
 
| Low
 
| Good
 
| Good
| ~10nm
+
| 5-20nm
 
| More conformal metal and dielectric thin film deposition.  Better than evaporation for maintaining stoichiometry of compounds
 
| More conformal metal and dielectric thin film deposition.  Better than evaporation for maintaining stoichiometry of compounds
 
|-
 
|-
 
| [[Parylene deposition| CVD Parylene Deposition]]
 
| [[Parylene deposition| CVD Parylene Deposition]]
 
| Parylene
 
| Parylene
| ~30-50Å/sec
+
| 25-50Å/sec
 
| 20ºC
 
| 20ºC
| Good Sidewall coverage
+
| Good
 
| Good
 
| Good
 
| Very Low
 
| Very Low
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| 5-200Å/sec
 
| 5-200Å/sec
 
| 200-400ºC
 
| 200-400ºC
| Some sidewall coverage
+
| OK
 
| Good
 
| Good
 
| Very Low
 
| Very Low
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| 10-100 Å/sec
 
| 10-100 Å/sec
 
| 600-1200ºC
 
| 600-1200ºC
| Isotropic - good sidewall coverage
+
| Very Good
 
| Very Good
 
| Very Good
 
| Very Low
 
| Very Low
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| 0.1-100 Å/sec
 
| 0.1-100 Å/sec
 
| 900-1200ºC
 
| 900-1200ºC
| Isotropic - very good sidewall coverage
+
| Very Good
 
| Very Good
 
| Very Good
 
| Very Low
 
| Very Low
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| Depends on process
 
| Depends on process
 
| 0-100ºC
 
| 0-100ºC
| Isotropic - good sidewall coverage
+
| Very Good
 
| Good
 
| Good
 
| Depends on process
 
| Depends on process
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| [[Atomic layer deposition|Atomic Layer Deposition (ALD)]]
 
| [[Atomic layer deposition|Atomic Layer Deposition (ALD)]]
 
| Metals, metal oxides and nitrides
 
| Metals, metal oxides and nitrides
| ~1Å/ cycle.   
+
| 0.1-3 Å/cycle.   
 
5-200 sec cycle
 
5-200 sec cycle
 
| 50-300ºC
 
| 50-300ºC
| Isotropic - very good sidewall coverage
+
| Very Good
 
| Good
 
| Good
 
| Low
 
| Low

Revision as of 14:58, 10 March 2016

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.

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 Conformality/Sidewall Coverage Film Density Impurity Levels Uniformity Grain Size Primarily Used for:
Evaporation Metals and Dielectrics 1-15 Å/sec 10-100ºC Poor-None Poor Low Poor 10-100nm Works well with liftoff patterning
Sputter deposition Metals and dielectrics 0.1-10 Å/sec 50-300ºC OK Good Low Good 5-20nm More conformal metal and dielectric thin film deposition. Better than evaporation for maintaining stoichiometry of compounds
CVD Parylene Deposition Parylene 25-50Å/sec 20ºC Good Good Very Low Good unknown Thick (0.8-75μm) encapsulation and insulation; Biocompatible
Plasma Enhanced CVD (PECVD) Mainly Dielectrics 5-200Å/sec 200-400ºC OK Good Very Low Good 10-100nm Lower temp oxide/nitride deposition
Low Pressure CVD (LPCVD) Mainly Dielectrics 10-100 Å/sec 600-1200ºC Very Good 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 Very Good Very Good Very Low Very Good 1-10nm Best quality oxide when substrate can handle higher temp and slower dep rate
ECD/Plating Conductive Materials Depends on process 0-100ºC Very Good 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 0.1-3 Å/cycle.

5-200 sec cycle

50-300ºC Very Good Good Low Very good 10-100nm Very thin, very conformal films such as 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 decompose and react on the substrate surface to produce the desired thin film material. CVD can be used to grow high quality, uniform thin films of various, mostly insulating or semiconducting, materials.

CVD can be subdivided into classifications based on pressure requirements (atmospheric (APCVD), low-pressure (LPCVD), and ultra-high vacuum (UHCVD)). LPCVD is used in the LNF to deposit silicon dioxide, silicon nitride, and doped and undoped polysilicon. 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. PECVD is used in the LNF to deposit silicon dioxide, silicon nitride, and amorphous silicon (a-Si:H). Catalytic CVD refers to CVD where the surface reaction is facilitated by the presence of a catalyst material on the substrate, or where the substrate itself is a catalyst for the growth reaction. Carbon nanotubes and graphene can be grown by catalytic CVD. Another type of CVD is metalorganic CVD, which uses organometallic gas precursors to grow III-V and II-VI compound semiconductors such as InP, GaN, AlGaAs, etc.


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.

Thermal Oxidation

Main article: Thermal oxidation

Thermal oxidation is used to grow very high quality silicon dioxide on silicon. By exposing silicon to oxygen at very high temperatures (~1000 C), the silicon and oxygen react and form silicon dioxide. Thermal oxidation is typically used to grow silicon dioxide for MOS transistor gates.

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)