WCl₅ in Semiconductor Manufacturing: Key Applications and Industry Developments

Introduction

1. Basic Information

2. Applications in Semiconductor Manufacturing Processes

Tungsten(V) chloride (WCl₅) is a fluorine-free tungsten precursor that has recently been used in semiconductor processes for the deposition of metallic tungsten and tungsten nitride (WNx) thin films. It is particularly applied in processes such as atomic layer deposition (ALD) and pulsed nucleation layer (PNL) techniques to form tungsten liner layers or nucleation layers.

Traditionally, tungsten thin films have mainly been deposited using tungsten hexafluoride (WF₆) precursors. However, the presence of fluorine can lead to electromigration or diffuse into adjacent components, corroding contacts and degrading device performance.

In contrast, tungsten chlorides (WClx) are fluorine-free, and their primary reaction byproduct is hydrogen chloride (HCl). Although HCl is corrosive, its effects are relatively easier to control, thereby avoiding fluorine contamination and substrate corrosion caused by WF₆.

In addition, compared with tungsten hexachloride (WCl₆), WCl₅ has a higher saturated vapor pressure at room temperature, making it easier to vaporize and transport into deposition chambers. This enables a more stable precursor supply in ALD/CVD processes. This characteristic makes WCl₅ a promising tungsten deposition precursor capable of replacing WF₆.

However, WCl₅ is a solid at room temperature and still belongs to the category of low vapor pressure precursors. In practical applications, the container must be heated and the delivery method optimized to ensure a stable vapor flow rate.

Some studies have improved its sublimation behavior by regulating the crystalline phase composition of WCl₅, ensuring stable precursor output during long deposition processes [1]. These measures are intended to overcome the supply challenges associated with solid precursors and improve the feasibility of WCl₅ in industrial deposition equipment.

Specific Applications

01 Metallic Tungsten Thin Films: High-Conformality Nucleation Layers and Bulk Layers

In ALD processes, WCl₅ can undergo self-limiting adsorption on substrate surfaces, followed by the introduction of reducing gases to convert it into metallic tungsten.

For example, alternating pulses of WCl₅ and reducing agents such as diborane (B₂H₆), silane (SiH₄), or hydrogen can be used to deposit tungsten nucleation layers [2]. WCl₅ can also be used in CVD processes to deposit bulk tungsten layers, producing tungsten films with extremely low chlorine content or even no detectable chlorine [3].

It should be noted that solid WCl₅ is preferably stored in glass containers to avoid corrosion [4]. During deposition, the temperatures of the container and delivery lines should generally be maintained within the range of 190–245°C to ensure sufficient vapor pressure for sublimation of solid WCl₅ and to maintain a stable vapor flow during transport [5].

Overall, WCl₅ has been used for depositing both nucleation layers and bulk layers of tungsten metal films, and tungsten filling in high aspect ratio structures can be achieved.

Commonly Used Reducing Agents:

① Hydrides such as hydrogen, silane, diborane, and organoborohydride reagents.

② Some studies have attempted reactions between WCl₅ and organoaluminum reagents (such as triethylaluminum), resulting in the formation of carbide phases (W–C) [6].

02 Tungsten Nitride Thin Films: Highly Thermally Stable Barrier Layers

WN thin films can serve as diffusion barrier layers for conductors such as copper or ruthenium. Experimental results show that ALD-WN layers with a thickness of approximately 4 nm can still block the diffusion of copper and ruthenium after annealing at temperatures as high as 850°C, demonstrating excellent thermal stability and barrier performance [7].

In a Lam Research patent [2], PE-ALD technology is used at relatively low temperatures by first introducing NH₃ onto dielectric surfaces for adsorption and decomposition, followed by WCl₅ introduction to react with the previously adsorbed nitrogen species and form high-quality WN thin films. This method enables the formation of uniform WN barrier layers on oxide surfaces.

Commonly Used Co-reactants:

① Common nitrogen source: NH₃.

② Nitrogen-containing organics (such as tert-butylhydrazine): produce carbon-containing W(N,C) co-deposited films [6].

③ Preferred nitrogen source: N₂/H₂, which not only provides active nitrogen species but also reduces chlorine residue through the reducing effect of hydrogen and promotes the formation of low-resistivity phases [7].

Applications in the Semiconductor Industry

As an emerging tungsten precursor, WCl₅ has demonstrated unique advantages and broad application potential in semiconductor thin film deposition.

Equipment manufacturer Lam Research began early research and development of WCl₅ for tungsten filling applications and has filed multiple patents in this field. On the materials supplier side, Air Liquide has also invested in the purification, storage, and transportation of WCl₅ and has applied for related patents to ensure high precursor purity and stable supply.

Among semiconductor device manufacturers, although public literature rarely directly states the use of WCl₅, publicly available information indicates that leading companies are already evaluating this material in research and development.

For example:

① Merck Electronics clearly states in its high-purity WCl₅ product overview that its applications include tungsten filling for metal gate contacts in logic devices and fluorine-free tungsten material deposition for memory devices such as DRAM and 3D NAND.

② Logic foundries and memory chip manufacturers such as TSMC, Intel, and Samsung may already be evaluating WCl₅ as a replacement for WF₆ in order to reduce fluorine-related damage to dielectric layers during processing.

③ Applied Materials has also mentioned fluorine-free tungsten solutions in its technology promotions and introduced new CVD systems capable of selective tungsten deposition. These systems may involve the use of tungsten chloride precursors to selectively deposit tungsten for channel filling on specific surfaces.

④ In the memory sector, companies such as Samsung and SK Hynix are more focused on using WCl₅ in buried word lines for 3D NAND and DRAM to avoid fluorine-induced corrosion of multilayer oxide films.

⑤ A white paper released by Entegris disclosed that in 3D NAND manufacturing processes, WCl₅ can effectively replace WF₆, thereby resolving defects such as line bending caused by fluorine. However, due to cost considerations, it has not yet been adopted for large-scale mass production.

Conclusion

As material supply chains improve and process technologies mature, WCl₅ is expected to play an increasingly important role in future semiconductor manufacturing. Some IDM companies or foundries may have already validated fluorine-free tungsten processes on pilot lines at 5 nm nodes and below to improve interconnect reliability.

At present, the industry’s attitude toward WCl₅ is both positive and cautious. It is widely regarded as a strong candidate for next-generation tungsten precursors, and leading material and equipment suppliers have already provided support for its development.

It is believed that major chip manufacturers, after balancing cost, safety, and process maturity, will gradually introduce WCl₅ into key process steps on a small scale and expand its applications after sufficient validation.

If you have any purchasing needs for tungsten (V) chloride, or would like to learn more, please feel free to email jomin@wolfachem.com and we will reply to you promptly.

References

[1] <Tungsten pentachloride conditioning and crystalline phase manipulation> US11577967B2

[2] <Methods of preparing tungsten and tungsten nitride thin films using tungsten chloride precursor> US9595470B2

[3] <Methods of preparing tungsten and tungsten nitride thin films using tungsten chloride precursor> US9595470B

[4]<Internally coated vessel for housing a metal halide> WO2017075172A1

[5]<Tungsten pentachloride conditioning and crystalline phase manipulation> US10710896B2

[6] Minyoung Lee, et al. Applied Surface Science, 2021, 563, 150373. DOI: 10.1016/j.apsusc.2021.150373

[7] KangMin Seo, et al. ACS Appl. Nano Mater. 2023, 6, 23, 21741-21751. DOI: 10.1021/acsanm.3c03956