Difference between revisions of "Physical vapor deposition"

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==See also==
 
==See also==
* [[Thermal evaporation]]
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* [[Evaporation]]
* [[Electron beam evaporation]]
 
 
* [[Sputter deposition]]
 
* [[Sputter deposition]]
 
* [[Deposition]]
 
* [[Deposition]]
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==Further reading==
 
==Further reading==
 
* LNF Technology seminar: PVD February 27, 2015: [http://leccap.engin.umich.edu/leccap/viewer/r/EQfS99 video recording] and [https://umich.box.com/s/8cy227xts0yhcq0jnoll4kffh3k60rni complete slides]
 
* LNF Technology seminar: PVD February 27, 2015: [http://leccap.engin.umich.edu/leccap/viewer/r/EQfS99 video recording] and [https://umich.box.com/s/8cy227xts0yhcq0jnoll4kffh3k60rni complete slides]

Revision as of 15:02, 10 March 2016

Physical vapor deposition
PVDoperation.jpg
Technology Details
Other Names PVD
Technology Deposition
Equipment List of PVD equipment

Physical vapor deposition (PVD) is a type of deposition where source materials are transformed into a vapor or plasma using a physical process (typically heating or physical bombardment.) The vapor then moves towards a substrate where it condenses on the substrate surface.

More details: LNF Technology seminar: PVD February 27, 2015: video recording and complete slides

Technologies

Evaporation

Main article: Evaporation

Evaporation is the method where source materials are heated to high temperatures where they melt or sublimate into a vapor. These atoms then precipitate into solid form, coating everything in the chamber, within line of sight, with a thin layer of the anode material. Typically this deposition is done in a vacuum to allow for a collision-free path of source material to the substrate and to reduce unwanted reactions, contamination and heat transfer.

The atoms in the vapor from evaporation have only thermal energy and strike the substrate with very little kinetic energy. When depositing thin films in a vacuum chamber that have no kinetic energy, only the light from the source will cause any heat transfer to the wafers. All the evaporators in the LNF are dome/liftoff tools with long throw distances and small/centered point sources. This makes them ideal for liftoff applications, depositions where the substrates cannot handle any plasma heating and thicker films. They are poorly suited for any application requiring sidewall coverage or controlled stress or stoichiometry.


Sputter deposition

Main article: Sputter deposition

Sputter Deposition involves exposing a target material to a plasma (typically Ar) which creates accelerated ions and electrons to "knock" off the target material into a cloud of source atoms. The source vapor then condenses onto the substrate forming a thin film.

Sputtering creates energetic atoms that move and collide as they travel thru the gas plasma towards the substrate. These atoms therefore come in at various angles and hit the substrate with some energy defined by the gas pressure and target voltage. Because of the non-normal nature of the plasma, sputtering does coat the sidewalls of the features on the substrate and the energy of the atoms causes heating of the substrate during deposition. The heating and sidewall coverage make sputtering less desirable for liftoff applications but more useful when conformal coatings are needed. Film stress and chemistry can also be better tuned in sputtering using plasma power/pressure settings and by injecting reactive gasses during deposition.


Figures of merit

Deposition rate

Deposition rate, usually expressed in Å/sec, is measured at the substrate using various methods. It is measured real-time in the evaporators and set using deposition time on the sputter tools.

Uniformity

Uniformity measures the variation in thickness across a substrate and is usually expressed as a percentage. Typically: (Thickness Max - Thickness Min)/Thickness Average. Uniformity is typically set by the material being deposited and the geometry of the system: throw distance, substrate rotation and deposition angle.

Stress

Stress is a a measure of the force that the film exhibits on itself and the substrate. It is usually measure in mega-Pascals (MPa) with positive stress being called "tensile" and negative stress referred to as "compressive." Stress in thin films can affect devices and substrates as well as poorly affect adhesion and other properties. In terms of deposition parameters, stress is affected by the energy and angle of the material as it strikes the substrate.

Resistivity

Resistivity is an electrical measurement of the characteristic of the film It can be measured on electrical structures (lengths of wiring lines) or on blanket films using the four-point probe. It is expressed in many units, typically μ-ohm-cm.

Resistivity is typically used to measure the quality of the film in terms of source purity or vacuum purity but it can be changed by altering the density of the film (pressure, power and bias during sputtering)

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.

See the technology pages to see more detailed descriptions on how deposition parameters can be used to alter these figures of merit:

Main article: Sputter deposition

Parameters

Power

Power in evaporation is typically heating boat (thermal) or electron emission current (e-beam) and while in the case of sputtering it is the plasma power which is dominated by current. Power is typically used to change deposition rate in the process. Power can be used to change film stress and substrate heating in sputtering but it usually does not change an evaporated film's characteristics.

Pressure

Base or Starting pressure is a measure of the quality of the initial vacuum. Lower base pressure generally leads to films with less impurities, mostly unwanted O2, H2O and N2

Deposition pressure in the case of sputtering is the amount of Ar (and sometimes reactive gas) used during deposition. Higher pressure leads to more collisions on the target surface and more collision of the material as it makes it's way to the substrate. In magnetron sputtering there is typically a optimal pressure spot where the highest deposition rates occur but the process may be run higher or lower than this spot to tune the film for a stress value

Substrate Bias and Heating

Substrate heating can change the behavior of the deposited film by changing the stress, adhesion (typically driving off water) or chemical reactions in the film. The affect of heating varies with the material being deposited.

Bias can increase the energy of incoming atoms and change the stress of the film. Also, bias can cause collisions at the substrate level and redeposit atoms so it can be used to try and increase sidewall coverage.

Materials

Many materials can be deposited using PVD. It is typically used for metals and harder insulators but, anything that can be heated to vaporization or bombarded, can be depositted. Typical limitations involve the quality of the deposited film (adhesion, other issues) or the suitability and safety of the material under vacuum.

Equipment

See the sub-categories for a general description of the PVD equipment at the LNF. For a complete list, please see list of PVD equipment.

See also

Further reading

Basic Overviews of PVD and Thin Film technology
  • Milton Ohring, Material Science of Thin Films, 2nd Edition, Academic Press, 2002.
  • J. L. Vossen and W. Kern, eds., Thin Film Processes. Academic Press, 1978.
  • Krishna Seshan, ed., Handbook of Thin Film Deposition, 3rd Ed, Elsevier, 2012
  • S. A Campbell, The Science and Engineering of Microelectronic Fabrication, 2nd Ed, Oxford Press, 2001