Tantalum capillary tubes: Advanced materials that solve the problem of gas delivery in CVD processes

In the fields of semiconductors, optical coatings, and advanced materials, chemical vapor deposition (CVD) and atomic layer deposition (ALD) technologies are at the core of driving innovation. The success or failure of these processes often hinges on a seemingly minor yet crucial component - the precision tubing used to transport the reactive precursor gases. Especially downstream of the mass flow controller (MFC), where the tubing directly connects to the reaction chamber, the material selection of the tubing directly determines the purity, yield, and cost of the product.

When the process involves highly reactive and corrosive precursor gases such as WF₆, HCl, HBr, Cl₂, F₂ and various metal organic compounds, the vast majority of metal materials will fail rapidly, causing catastrophic contamination. Only one type of metal material can handle this extreme environment with ease: tantalum capillary tubes.

Why is tantalum micro tube the only preferred choice for the downstream gas line of MFC?
Tantalum is a rare refractory metal, and its inherent physical and chemical properties make it the perfect choice for demanding CVD/ALD applications.
Tantalum's most remarkable property is its extremely high chemical inertness. At room temperature, it hardly reacts with any acid, including aqua regia. It is only corroded in a hot and concentrated alkaline environment or in hydrofluoric acid. This means that for the vast majority of highly corrosive CVD precursor gases, a dense and stable passivation oxide film (Ta₂O₅) forms on the tantalum surface, effectively preventing further corrosion reactions and ensuring the absolute purity of the transported gas.

Extremely high material purity
The semiconductor-grade CVD process demands extremely high purity. High-purity tantalum capillary tubes (such as 4N5 - 99.995% and above) themselves contain almost no volatile or migratory impurity elements, fundamentally eliminating the risk of contamination caused by the tubing material itself and preventing the formation of defects on the wafer.

Outstanding machinability and sealing performance
Tantalum has excellent ductility and can be drawn into precision capillary tubes with uniform wall thickness and precise inner diameter dimensions. It has good compatibility with common compression fittings and can achieve ultra-high vacuum (UHV) sealing, ensuring the integrity and leak-free operation of gas delivery systems.

High-temperature resistance property
Tantalum has a melting point as high as 3017°C, far exceeding the temperature required for preheating gases in the CVD process. Tantalum gas pipelines can maintain strength and stability for a long time in high-temperature environments, effectively preventing gas condensation within the pipes, thereby ensuring process repeatability and the accuracy of gas proportion control.

Application scenarios of tantalum capillary tubes in CVD/ALD gas delivery systems
The final leg downstream of the MFC: As the final section of tubing connecting the mass flow controller (MFC) and the reaction chamber, this is the "choke point" of the entire gas supply system. Here, tantalum material must be used to protect the precisely metered gas from the MFC from being contaminated before entering the reaction zone. Transportation of highly reactive halogen gases: such as WF₆ (tungsten hexafluoride) for tungsten deposition, Cl₂ (chlorine) and HBr (hydrogen bromide) for etching processes, etc. Transport of metal-organic precursors (MO sources): for MOCVD processes, to grow compound semiconductors. Special applications: In vacuum and gas control systems of research-grade ALD equipment, particle accelerator beamlines, and fusion reaction devices, tantalum capillaries are also indispensable key components.

How to choose qualified tantalum capillary tubes?
Not all tantalum tubes can meet the strict semiconductor standards. When purchasing, it is essential to confirm the following key parameters:
Material Purity: 99.95% (3N5) or above is required, and ideally it should be 99.995% (4N5).
Dimensions & Tolerance: Precise outer diameter (OD), inner diameter (ID), and wall thickness (Wall Thickness), typically with an outer diameter ranging from 1/8 inch to 1/4 inch, and an inner diameter that is smaller.

Surface Finish: The inner and outer walls must have extremely low roughness (Ra value) to reduce gas turbulence and particle adhesion.

Certification & Traceability: Complete material certification certificates (Mill Certificate) must be provided to ensure traceability of composition and performance.

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