Chemistry:Tantalum nitride

Tantalum nitride
Names
	Other names Tantalum mononitride
Identifiers
CAS Number	12033-62-4 ;
3D model (JSmol)	Interactive image;
EC Number	234-788-4;
PubChem CID	82832;
	InChI InChI=1S/N.Ta;
	SMILES N#[Ta];
Properties
Chemical formula	TaN
Molar mass	194.955 g/mol
Appearance	black crystals
Density	14.3 g/cm3
Melting point	3,090 °C (5,590 °F; 3,360 K)
Solubility in water	insoluble
Structure
Crystal structure	Hexagonal, hP6
Space group	P-62m, No. 189
Hazards
Flash point	Non-flammable
Related compounds
Other cations	Vanadium nitride; Niobium nitride
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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	Infobox references

Tantalum nitride (TaN) is a chemical compound, a nitride of tantalum. There are multiple phases of compounds, stoichimetrically from Ta₂N to Ta₃N₅, including TaN.

As a thin film TaN find use as a diffusion barrier and insulating layer between copper interconnects in the back end of line of computer chips. Tantalum nitrides are also used in thin film resistors.

Phase diagram

The tantalum - nitrogen system includes several states including a nitrogen solid solution in Tantalum, as well as several nitride phases, which can vary from expected stoichiometry due to lattice vacancies.^[1] Annealing of nitrogen rich "TaN" can result in conversion to a two phase mixture of TaN and Ta₅N₆.^[1]

Ta₅N₆ is thought to be the more thermally stable compound - though it decomposes in vacuum at 2500C to Ta₂N.^[1] It was reported the decomposition in vacuum from Ta₃N₅ via Ta₄N₅, Ta₅N₆, ε-TaN, to Ta₂N.^[2]

Preparation

TaN is often prepared as thin films. Methods of depositing the films include RF-magnetron-reactive sputtering,^[3]^[4] Direct current (DC) sputtering,^[5] Self-propagating high-temperature synthesis (SHS) via 'combustion' of Tantalum powder in Nitrogen,^[1] low‐pressure metalorganic chemical vapor deposition (LP‐MOCVD),^[6] ion beam assisted deposition (IBAD),^[7] and by electron beam evaporation of tantalum in concert with high energy nitrogen ions.^[8]

Depending on the relative amount of N₂, the deposited film can vary from (fcc) TaN to (hexagonal) Ta₂N as nitrogen decreases.^[4] A variety of other phases have also been reported from deposition including bcc and hexagonal TaN; hexagonal Ta₅N₆; tetragonal Ta₄N₅; orthorhombic Ta₆N_2.5, Ta₄N, or Ta₃N₅.^[4] The electrical properties of TaN films vary from metallic conductor to insulator depending on the relative nitrogen ratio, with N rich films being more resistive.^[9]

Uses

It is sometimes used in integrated circuit manufacture to create a diffusion barrier or "glue" layers between copper, or other conductive metals. In the case of BEOL processing (at c. 20 nm), copper is first coated with tantalum, then with TaN using physical vapour deposition (PVD); this barrier coated copper is then coated with more copper by PVD, and infilled with electrolytically coated copper, before being mechanically processed (grind/polishing).^[10]

It also has application in thin film resistors.^[3] It has the advantage over nichrome resistors of forming a passivating oxide film which is resistant to moisture.^[11]

References

↑ ^1.0 ^1.1 ^1.2 ^1.3 Borovinskaya, Inna P. (2017). Concise Encyclopedia of Self-Propagating High-Temperature Synthesis - History, Theory, Technology, and Products. pp. 370–371. doi:10.1016/B978-0-12-804173-4.00150-2. ISBN 9780128041734.
↑ Terao, Nobuzo (1971), "Structure of Tantalum Nitrides", Japanese Journal of Applied Physics 10 (2): 248–259, doi:10.1143/JJAP.10.248, Bibcode: 1971JaJAP..10..248T
↑ ^3.0 ^3.1 Akashi, Teruhisa (2005), "Fabrication of a Tantalum-Nitride Thin-Film Resistor with a Low-Variability Resistance", IEEJ Transactions on Sensors and Micromachines 125 (4): 182–187, doi:10.1541/ieejsmas.125.182, Bibcode: 2005IJTSM.125..182A
↑ ^4.0 ^4.1 ^4.2 Zaman, Anna; Meletis, Efstathios I. (23 November 2017), "Microstructure and Mechanical Properties of TaN Thin Films Prepared by Reactive Magnetron Sputtering", Coatings 7 (12): 209, doi:10.3390/coatings7120209
↑ Lima, Lucas; Moreiraa, Milena D.; Cioldin, Fred; Diniza, José Alexandre; Doi, Ioshiaki (2010), "Tantalum Nitride as Promising Gate Electrode for MOS Technology", ECS Trans. 31 (1): 319–325, doi:10.1149/1.3474175, Bibcode: 2010ECSTr..31a.319L
↑ Tsai, M. H.; Sun, S. C. (1995), "Metalorganic chemical vapor deposition of tantalum nitride by tertbutylimidotris(diethylamido)tantalum for advanced metallization", Appl. Phys. Lett. 67 (8): 1128, doi:10.1063/1.114983, Bibcode: 1995ApPhL..67.1128T
↑ Baba, K.; Hatada, R.; Udoh, K.; Yasuda, K. (2 May 1997), "Structure and properties of NbN and TaN films prepared by ion beam assisted deposition", Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 127–128: 841–845, doi:10.1016/S0168-583X(97)00018-9, Bibcode: 1997NIMPB.127..841B
↑ Ensinger, W.; Kiuchi, M.; Satou, M. (1995), "Low‐temperature formation of metastable cubic tantalum nitride by metal condensation under ion irradiation", Journal of Applied Physics 77 (12): 6630, doi:10.1063/1.359073, Bibcode: 1995JAP....77.6630E
↑ Kim, Deok-kee; Lee, Heon; Kim, Donghwan; Kim, Young Keun (October 2005), "Electrical and mechanical properties of tantalum nitride thin films deposited by reactive sputtering", Journal of Crystal Growth 283 (3–4): 404–408, doi:10.1016/j.jcrysgro.2005.06.017, Bibcode: 2005JCrGr.283..404K
↑ LaPedus, Mark (26 June 2012), "Challenges Mount For Interconnect", semiengineering.com, https://semiengineering.com/challenges-mount-for-interconnect/
↑ Licari, James J.; Enlow, Leonard R. (1998), Hybrid Microcircuit technology Handbook (2nd ed.), Noyes Publications, § 2.5 Characteristics of Tantalum Nitride Resistors, pp.83-4