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=Vanadium Nitride (WN<sub>x</sub>)=
=Vanadium Nitride (VN<sub>x</sub>)=


Tungsten nitride (WNₓ, commonly W₂N or δ‑WN) is a refractory ceramic that combines very high melting temperature, extreme hardness, chemical inertness, and good electrical conductivity in a composition‑tunable, CMOS‑compatible matrix.
Vanadium nitride (VN<sub>x</sub>, commonly cubic &delta;-VN near the stoichiometric composition) is a refractory transition-metal nitride that combines high hardness, good thermal and chemical stability, and metallic electrical conductivity. Its properties depend strongly on the N/V ratio, vacancy concentration, strain, crystalline quality, film thickness and oxygen contamination. Reactive magnetron sputtering therefore provides considerable control over the phase, microstructure, resistivity and superconducting behaviour of VN<sub>x</sub> films.
Thin films are produced chiefly by reactive magnetron sputtering, where nitrogen flow and substrate temperature set stoichiometry and phase, yielding dense layers with controllable resistivity and stress.
In semiconductor process flows, WNₓ acts as a robust Cu diffusion barrier/liner, hard mask, gate or contact material, and precision thin‑film resistor; its high absorption coefficient also makes it the standard absorber layer in EUV lithography photomasks and a candidate for x‑ray mask blanks.
Optically, WN-based stacks offer durable, high-temperature plasmonic and thermally emissive coatings, mid-IR absorbers, and multilayer structures for soft-x-ray mirrors and synchrotron beamline optics, delivering stability far beyond noble metals under extreme photon flux.
Beyond electronics and photonics, the material’s wear and oxidation resistance support MEMS springs, high‑temperature sensors, and corrosion‑resistant coatings, while select WN phases become superconducting below roughly 3–5 K, enabling niche low‑loss microwave resonators and detector elements that benefit from its mechanical robustness and diffusion‑barrier capability.


== Deposition of Tungsten Nitride ==
A particularly important property of VN is superconductivity. High-quality reactively sputtered films can exhibit superconducting transition temperatures, <i>T</i><sub>c</sub>, approaching 9 K, while thinner or more disordered films generally show lower and broader transitions. Because <i>T</i><sub>c</sub> is sensitive to nitrogen vacancies, strain and lattice parameters, deposition conditions and subsequent processing must be carefully controlled when the films are intended for cryogenic devices.
 
VN is being investigated as an alternative superconducting nitride for quantum and low-temperature technologies. Demonstrated or proposed applications include superconducting nanowire single-photon detectors, terahertz and infrared hot-electron bolometers, low-loss microwave components and resonators, and other superconducting structures in which kinetic inductance and fast non-equilibrium electron dynamics are important. Single-photon detectors are particularly relevant to quantum communication, quantum optics, photon-counting experiments and low-light imaging. VN remains less established than NbN, NbTiN or TiN, but its combination of superconductivity, mechanical robustness and compatibility with reactive sputter deposition makes it an interesting material for further quantum-device development.
 
Outside superconducting applications, VN<sub>x</sub> is also studied as a hard and wear-resistant coating, a conductive diffusion-barrier material, and an electrode or catalyst material. In all these applications, stoichiometry and defect structure are decisive; nominal N<sub>2</sub> percentage in the sputtering gas should therefore not be interpreted directly as the value of <i>x</i> in VN<sub>x</sub>.
 
==Deposition of Vanadium Nitride==
   
   
Deposition of VN<sub>x</sub> can only be done by reactive sputtering using a V target.
At DTU Nanolab, VN<sub>x</sub> thin films are deposited by reactive sputtering from an elemental V target in an Ar/N<sub>2</sub> atmosphere.


The tool of choice for this application is the Cluster-based multi-chamber high-vacuum sputtering deposition system, commonly referred to as the "[[Specific Process Knowledge/Thin film deposition/Cluster-based multi-chamber high vacuum sputtering deposition system|Cluster Lesker]]." The operating process is described in detail.:
The preferred tool for this application is the cluster-based multi-chamber high-vacuum sputtering system, commonly referred to as the "[[Specific Process Knowledge/Thin film deposition/Cluster-based multi-chamber high vacuum sputtering deposition system|Cluster Lesker]]." The qualified process is described in detail here:






* [[Specific Process Knowledge/Thin film deposition/Deposition of Vanadium Nitride/VN Reactive Sputtering in Cluster Lesker PC1|Deposition of Vanadium Nitride (VN<sub>x</sub>) using reactive pulsed DC sputtering in Sputter-System Metal-Oxide(PC1) Source 5 (3-inch target)]]
* [[Specific Process Knowledge/Thin film deposition/Deposition of Vanadium Nitride/VN Reactive Sputtering in Cluster Lesker PC1|Deposition of Vanadium Nitride (VN<sub>x</sub>) using reactive pulsed-DC sputtering in Sputter-System Metal-Oxide (PC1), Source 5 (3-inch target)]]






At the moment (October 2026), we have a 3-inch V target (0.125" thick) for PC3 or PC1.
As of October 2026, a 3-inch V target with a thickness of 0.125 inches is available for use in PC1 or PC3.


==Comparison of sputter systems for reactive deposition==
==Comparison of sputter systems for reactive deposition==
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|-style="background:silver; color:black"
|-style="background:silver; color:black"
!
!
![[Specific_Process_Knowledge/Thin_film_deposition/Cluster-based_multi-chamber_high_vacuum_sputtering_deposition_system|Sputter-System Metal-Nitride(PC1)]]
![[Specific_Process_Knowledge/Thin_film_deposition/Cluster-based_multi-chamber_high_vacuum_sputtering_deposition_system|Sputter-System Metal-Oxide (PC1)]]
![[Specific_Process_Knowledge/Thin_film_deposition/Cluster-based_multi-chamber_high_vacuum_sputtering_deposition_system|Sputter-System Metal-Nitride(PC3)]]
![[Specific_Process_Knowledge/Thin_film_deposition/Cluster-based_multi-chamber_high_vacuum_sputtering_deposition_system|Sputter-System Metal-Nitride (PC3)]]
|-
|-


|-
|-
|-style="background:WhiteSmoke; color:black"
|-style="background:WhiteSmoke; color:black"
!Generel description
!General description
|
|
*reactive Pulsed DC
*Reactive pulsed DC
*reactive HIPIMS (high-power impulse magnetron sputtering)  
*Reactive HiPIMS (high-power impulse magnetron sputtering)  
|
|
*reactive Pulsed DC
*Reactive pulsed DC
*reactive HIPIMS (high-power impulse magnetron sputtering)  
*Reactive HiPIMS (high-power impulse magnetron sputtering)  
|-
|-


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!Film thickness
!Film thickness
|
|
*Limited by process time.
*Limited by process time
*Deposition rate around 0.1 nm/s) depends on Ar/N<sub>2</sub> ratio and power.
*Deposition rate is approximately 0.1 nm/s and depends on the Ar/N<sub>2</sub> ratio and applied power


|
|
*Limited by process time.
*Limited by process time
*Deposition rate around 0.1 nm/s) depends on Ar/N<sub>2</sub> ratio and power.
*Deposition rate is approximately 0.1 nm/s and depends on the Ar/N<sub>2</sub> ratio and applied power
|-
|-


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|
|
*Deposition on one side of the substrate
*Deposition on one side of the substrate
*Properties including tunable stoichiometry
*Film properties, including stoichiometry, can be tuned through the process parameters
|
|
*Deposition on one side of the substrate
*Deposition on one side of the substrate
*Properties including tunable stoichiometry
*Film properties, including stoichiometry, can be tuned through the process parameters
|-
|-


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|
|
*Many smaller samples
*Many smaller samples
*Up to 10 100 mm or 150 mm wafers  
*Up to ten 100 mm or 150 mm wafers  
|
|
*Many smaller samples
*Many smaller samples
*Up to 10 100 mm or 150 mm wafers  
*Up to ten 100 mm or 150 mm wafers  
|-
|-


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!'''Allowed materials'''
!'''Allowed materials'''
|
|
*Almost any as long as they do not outgas and are not very toxic, see cross-contamination sheets
*Most vacuum-compatible materials, provided that they do not outgas significantly and are not highly toxic; see the cross-contamination sheets
|
|
*Almost any as long as they do not outgas and are not very toxic, see cross-contamination sheets
*Most vacuum-compatible materials, provided that they do not outgas significantly and are not highly toxic; see the cross-contamination sheets
|-
|-
|}
|}


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<br clear="all" />
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Deposition of Silicon Nitride can be done with either LPCVD (Low Pressure Chemical Vapor Deposition) or PECVD (Plasma Enhanced Chemical Vapor Deposition).
==Deposition of Silicon Nitride using LPCVD==
LPCVD silicon nitride can be deposited in a [[Specific Process Knowledge/Thin film deposition/B2 Furnace LPCVD Nitride|LPCVD nitride furnace]]. DTU Nanolab has two LPCVD nitride furnaces: A new furnace (installed in 2008) for deposition of stoichiometric nitride on 4" or on 6" wafers and an older furnace (installed in 1995) for deposition of stoichiometric nitride and low stress nitride on 4" wafers.
The LPCVD nitride deposition is a batch process, meaning that nitride can be deposited on a batch of up to 15 wafers (in the old nitride furnace) or 25 wafers (in the new nitride furnace) at a time. The deposition takes place at temperatures of 780-845 degrees Celsius and at a pressure of 120-200 mTorr. The LPCVD silicon nitride has a good step coverage, and the film thickness is very uniform over the wafers. On the furnaces there are standard processes for deposition of stoichiometric nitride (Si<sub>3</sub>N<sub>4</sub>) and for deposition of low stress nitride (SRN) (only on the old nitride furnace).
*[[/Deposition of Silicon Nitride using LPCVD|Deposition of Silicon Nitride using LPCVD]]
==Deposition of Silicon Nitride using PECVD==
PECVD nitride and oxynitride can be deposited in one of the [[Specific Process Knowledge/Thin film deposition/PECVD|PECVD]] systems at DTU Nanolab. You can run 1-3 wafers on several smaller chips at a time depending on which one of the PECVD's you use. The deposition takes place at 300 degrees Celsius. This can be of importance for some applications, but it gives a less dense film compared to LPCVD nitride, and the stoichiometry is on the following form: Si<sub>x</sub>N<sub>y</sub>O<sub>z</sub>H<sub>v</sub>. The step coverage and the thickness uniformity of the film are not as good as for the LPCVD nitride. In one of our PECVD systems (PECVD3) we allow small amounts of metal on the wafers entering the system; this is not allowed in the LPCVD furnace and in the clean PECVD (PECVD1). We also have a PECVD for deposition on III-V materials (PECVD2).
*[[/Deposition of Silicon Nitride using PECVD|Deposition of Silicon Nitride using PECVD]] - ''or oxynitride''
==Comparison of LPCVD and PECVD for silicon nitride deposition==
{| border="1" cellspacing="0" cellpadding="3" align="center"
!
! [[Specific Process Knowledge/Thin film deposition/Furnace LPCVD Nitride|LPCVD]]
! [[Specific Process Knowledge/Thin film deposition/PECVD|PECVD]]
|-
| Stoichiometry
|
*Si<sub>3</sub>N<sub>4</sub>
*SRN (only old nitride furnace, only 4" wafers)
Si<sub>3</sub>N<sub>4</sub>: Stoichiometric nitride
SRN: Silicon rich nitride (low stress nitride)
|
*Si<sub>x</sub>N<sub>y</sub>H<sub>z</sub>
*Si<sub>x</sub>O<sub>y</sub>N<sub>z</sub>H<sub>v</sub>
Silicon nitride can be doped with boron, phosphorus or germanium
|-
|Film thickness
|
*Si<sub>3</sub>N<sub>4</sub>: ~50 Å - ~1400 Å
*SRN: ~50 Å - ~2800 Å
Thicker nitride layers can be deposited over more runs
|
*~40 nm - 10 µm
|-
|Process temperature
|
*780 <sup>o</sup>C - 845 <sup>o</sup>C
|
*300 <sup>o</sup>C
|-
|Step coverage
|
*Good
|
*Less good
|-
|Film quality
|
*Deposition on both sides of the substrate
*Dense film
*Few defects
|
*Deposition on one side of the substrate
*Less dense film
*Incorporation of hydrogen in the film
|-
|Batch size
|
Old nitride furnace:
*1-17 4" wafers per run
New nitride furnace:
*1-25 4" or 6" wafers per run
|
*1-3 4" wafers or one 6" wafer or many smaller chips per run
|-
| Substrate materials allowed
|
*Silicon wafers (new wafers or RCA cleaned wafers)
**with layers of silicon oxide or silicon (oxy)nitride (RCA cleaned)
**from furnaces in stack A or B in cleanroom 2
*Pure quartz (fused silica) wafers (RCA cleaned)
|
*Silicon wafers
**with layers of silicon oxide or silicon (oxy)nitride
*Quartz wafers
*Small amounts of metal < 5% of the wafer coverage (ONLY in PECVD3!)
|-
| Etch rate in 80 <sup>o</sup>C KOH
|Expected <1 Å/min
|Dependent on recipe: ~1-10 Å/min
|-
| Etch rate in BHF
|Very low
|Very high compared to the etch rate of LPCVD nitride
|-
|}
-->

Revision as of 18:16, 13 October 2026

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Vanadium Nitride (VNx)

Vanadium nitride (VNx, commonly cubic δ-VN near the stoichiometric composition) is a refractory transition-metal nitride that combines high hardness, good thermal and chemical stability, and metallic electrical conductivity. Its properties depend strongly on the N/V ratio, vacancy concentration, strain, crystalline quality, film thickness and oxygen contamination. Reactive magnetron sputtering therefore provides considerable control over the phase, microstructure, resistivity and superconducting behaviour of VNx films.

A particularly important property of VN is superconductivity. High-quality reactively sputtered films can exhibit superconducting transition temperatures, Tc, approaching 9 K, while thinner or more disordered films generally show lower and broader transitions. Because Tc is sensitive to nitrogen vacancies, strain and lattice parameters, deposition conditions and subsequent processing must be carefully controlled when the films are intended for cryogenic devices.

VN is being investigated as an alternative superconducting nitride for quantum and low-temperature technologies. Demonstrated or proposed applications include superconducting nanowire single-photon detectors, terahertz and infrared hot-electron bolometers, low-loss microwave components and resonators, and other superconducting structures in which kinetic inductance and fast non-equilibrium electron dynamics are important. Single-photon detectors are particularly relevant to quantum communication, quantum optics, photon-counting experiments and low-light imaging. VN remains less established than NbN, NbTiN or TiN, but its combination of superconductivity, mechanical robustness and compatibility with reactive sputter deposition makes it an interesting material for further quantum-device development.

Outside superconducting applications, VNx is also studied as a hard and wear-resistant coating, a conductive diffusion-barrier material, and an electrode or catalyst material. In all these applications, stoichiometry and defect structure are decisive; nominal N2 percentage in the sputtering gas should therefore not be interpreted directly as the value of x in VNx.

Deposition of Vanadium Nitride

At DTU Nanolab, VNx thin films are deposited by reactive sputtering from an elemental V target in an Ar/N2 atmosphere.

The preferred tool for this application is the cluster-based multi-chamber high-vacuum sputtering system, commonly referred to as the "Cluster Lesker." The qualified process is described in detail here:



As of October 2026, a 3-inch V target with a thickness of 0.125 inches is available for use in PC1 or PC3.

Comparison of sputter systems for reactive deposition

Sputter-System Metal-Oxide (PC1) Sputter-System Metal-Nitride (PC3)
General description
  • Reactive pulsed DC
  • Reactive HiPIMS (high-power impulse magnetron sputtering)
  • Reactive pulsed DC
  • Reactive HiPIMS (high-power impulse magnetron sputtering)
Stoichiometry
  • Tunable
  • Tunable
Film thickness
  • Limited by process time
  • Deposition rate is approximately 0.1 nm/s and depends on the Ar/N2 ratio and applied power
  • Limited by process time
  • Deposition rate is approximately 0.1 nm/s and depends on the Ar/N2 ratio and applied power
Process temperature
  • Up to 600 °C
  • Up to 600 °C
Step coverage
  • Some step coverage possible
  • Some step coverage possible
Film quality
  • Deposition on one side of the substrate
  • Film properties, including stoichiometry, can be tuned through the process parameters
  • Deposition on one side of the substrate
  • Film properties, including stoichiometry, can be tuned through the process parameters
Batch size
  • Many smaller samples
  • Up to ten 100 mm or 150 mm wafers
  • Many smaller samples
  • Up to ten 100 mm or 150 mm wafers
Allowed materials
  • Most vacuum-compatible materials, provided that they do not outgas significantly and are not highly toxic; see the cross-contamination sheets
  • Most vacuum-compatible materials, provided that they do not outgas significantly and are not highly toxic; see the cross-contamination sheets


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