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=Tungsten Nitride (WN<sub>x</sub>)=
=Tungsten Nitride (WN<sub>x</sub>)=


Scandium nitride (ScN) is a rocksalt‑structure semiconductor with an indirect bandgap near 0.9 eV and a direct transition around 2.1 eV, combining high electron mobility, excellent thermal stability, and notable hardness in a chemically inert matrix.
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.
It is deposited by reactive magnetron sputtering for dense, textured films and by atomic layer deposition (ALD) when ultra-conformal, thickness-precise coatings are required on high-aspect-ratio or temperature-sensitive structures.
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 microelectronics, ScN functions as a diffusion barrier or seed layer, a lattice‑matched buffer for GaN/AlGaN power devices, and an emerging channel or contact material for high‑mobility transistors and thermoelectric modules.
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.
During reactive sputtering of AlN, elemental Sc is routinely co‑sputtered to form Al₁₋ₓScₓN, whose enhanced piezoelectric coefficients and ferroelectric phases enable next‑generation MEMS resonators, RF filters, and non‑volatile FeFET memories.
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.
Optically, ScN’s tunable plasma frequency supports near‑IR plasmonics, hot‑carrier photodetectors, and durable high‑temperature absorbers, while doped ScN shows adjustable n‑type conductivity and potential room‑temperature ferromagnetism for spintronic devices.
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.
Its high hardness, oxidation resistance, and decent thermal conductivity further suit ScN for protective coatings, MEMS layers, and thermoelectric power generators in harsh environments, underscoring its versatility across semiconductor, photonic, and engineering applications.


== Deposition of Scandium Nitride ==
== Deposition of Tungsten Nitride ==
   
   
Deposition of ScN can only be done by reactive sputtering using Sc target.
Deposition of WN<sub>x</sub> can only be done by reactive sputtering using W target.


The only tool for this application is the Cluster-based multi-chamber high vacuum sputtering deposition system, commonly referred to as the 'Cluster Lesker.' The operating process is thoroughly documented and described in detail.:
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.:


* [[Specific Process Knowledge/Thin film deposition/Deposition of Scandium Nitride/ScN Reactive Sputtering in Cluster Lesker PC3|Deposition of Scandium Nitride (ScN) using reactive sputtering]] in Sputter-System Metal-Nitride(PC3) Source 1 (4-inch target)


At the moment (October 2023) we have a 4-inch Sc target (0.250" thick, bonded to Cu) for PC3 Src1.
 
* [[Specific Process Knowledge/Thin film deposition/Deposition of Tungsten Nitride/WN Reactive Sputtering in Cluster Lesker PC3|Deposition of Tungsten Nitride (WN) using reactive sputtering]] in Sputter-System Metal-Nitride(PC3) Source 2 (3-inch target)
 
 
 
At the moment (July 2025) we have a 3-inch W target (0.125" thick, bonded to Cu) for PC3 or PC1.
 
==Comparison of sputter systems for reactive deposition==
 
{|border="1" cellspacing="1" cellpadding="3" style="text-align:left;"
|-
 
|-
|-style="background:silver; color:black"
!
![[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/Lesker|Lesker sputter system]]
|-
 
|-
|-style="background:WhiteSmoke; color:black"
!Generel description
|
*reactive DC/Pulsed DC
*reactive HIPIMS (high-power impulse magnetron sputtering)
|
*reactive DC sputtering (not tested)
|-
 
|-
|-style="background:LightGrey; color:black"
!Stoichiometry
|
*Tunable
|
*Tunable
|-
 
|-
|-style="background:WhiteSmoke; color:black"
!Film thickness
|
*Limited by process time.
*Deposition rate (0.2 nm/s) is likely faster than Sputter-System (Lesker)
 
|
*Limited by process time.
*Deposition rate unknown
|-
 
|-
|-style="background:LightGrey; color:black"
!Process temperature
|
*Up to 600 °C
|
*Up to 400 °C (Room temperature from 2021)
|-
 
|-
|-style="background:WhiteSmoke; color:black"
!Step coverage
|
*Some step coverage possible
|
*Some step coverage possible but amount unknown
|-
 
|-
|-style="background:LightGrey; color:black"
!Film quality
|
*Deposition on one side of the substrate
*Properties including tunable stoichiometry (requires process development)
|
*Deposition on one side of the substrate
*Unknown quality
*Likely O-contamination
|-
 
|-
|-style="background:WhiteSmoke; color:black"
!Batch size
|
*Many smaller samples
*Up to 10*100 mm or 150 mm wafers
|
*Several smaller samples
*1-several 50 mm wafers
*1*100 mm wafers
*1*150 mm wafer
|-
 
|-
|-style="background:LightGrey; color:black"
!'''Allowed materials'''
|
*Almost any as long as they do not outgas and are not very toxic, see cross-contamination sheets
|
*Almost any as long as they do not outgas and are not very toxic, see cross-contamination sheets
|-
|}
 
<br clear="all" />
 
 
 
 
 
 
<!--
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
|-
|}
-->

Latest revision as of 19:05, 30 July 2025

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Tungsten Nitride (WNx)

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. 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

Deposition of WNx can only be done by reactive sputtering using W target.

The tool of choice for this application is the Cluster-based multi-chamber high vacuum sputtering deposition system, commonly referred to as the "Cluster Lesker." The operating process is described in detail.:



At the moment (July 2025) we have a 3-inch W target (0.125" thick, bonded to Cu) for PC3 or PC1.

Comparison of sputter systems for reactive deposition

Sputter-System Metal-Nitride(PC3) Lesker sputter system
Generel description
  • reactive DC/Pulsed DC
  • reactive HIPIMS (high-power impulse magnetron sputtering)
  • reactive DC sputtering (not tested)
Stoichiometry
  • Tunable
  • Tunable
Film thickness
  • Limited by process time.
  • Deposition rate (0.2 nm/s) is likely faster than Sputter-System (Lesker)
  • Limited by process time.
  • Deposition rate unknown
Process temperature
  • Up to 600 °C
  • Up to 400 °C (Room temperature from 2021)
Step coverage
  • Some step coverage possible
  • Some step coverage possible but amount unknown
Film quality
  • Deposition on one side of the substrate
  • Properties including tunable stoichiometry (requires process development)
  • Deposition on one side of the substrate
  • Unknown quality
  • Likely O-contamination
Batch size
  • Many smaller samples
  • Up to 10*100 mm or 150 mm wafers
  • Several smaller samples
  • 1-several 50 mm wafers
  • 1*100 mm wafers
  • 1*150 mm wafer
Allowed materials
  • Almost any as long as they do not outgas and are not very toxic, see cross-contamination sheets
  • Almost any as long as they do not outgas and are not very toxic, see cross-contamination sheets





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