What gases can be used in vacuum tube CVD electric furnaces?

The gas inlet capability of a vacuum tube CVD electric furnace is one of its core functions. By precisely controlling the gas type, flow rate, and ratio, it can achieve the deposition, synthesis, or surface modification of various materials. The following is a detailed classification and typical application scenarios of the gas that can be introduced:

1. Inert gas: protective atmosphere and carrier gas
Argon gas (Ar)
Characteristics: chemically stable, does not participate in reactions, commonly used to provide an inert protective environment.
Application scenarios:
Prevent metals such as copper and aluminum from oxidizing at high temperatures, for example, as carrier gases in semiconductor metal film deposition.
As a dilution gas, adjust the concentration of the reaction gas and control the deposition rate.
In the synthesis of carbon nanotubes, argon gas is used as a carrier gas to carry carbon sources (such as acetylene) into the reaction chamber.
Nitrogen (N ₂)
Characteristics: May react with certain metals to form nitrides at high temperatures, but exhibits strong inertness at room temperature.
Application scenarios:
In the epitaxial growth of gallium nitride (GaN), nitrogen gas acts as a nitrogen source and reacts with gallium sources (such as trimethyl gallium).
As a protective gas, it prevents materials from reacting with oxygen at high temperatures, such as replacing air atmosphere in ceramic sintering.
Helium (He)
Characteristics: High thermal conductivity, suitable for processes that require rapid thermal homogenization.
Application scenarios:
In optical thin film deposition, helium gas as a carrier gas can enhance the uniformity of the film.
As a cooling gas, it assists in controlling the temperature distribution inside the furnace.

2. Reactive gas: directly involved in material synthesis
Carbon source gas
Methane (CH ₄):
Used for depositing diamond films, carbon nanotubes, or graphene.
Typical process: At high temperatures (800-1200 ℃), methane is cracked to generate carbon atoms, which deposit on the substrate surface to form diamond structures.
Acetylene (C ₂ H ₂):
Higher carbon content, suitable for rapid deposition of carbon materials such as silicon carbide coatings.
For example, depositing silicon carbide coating on the surface of aircraft engine blades to enhance high temperature resistance.
Silicon source gas
Silane (SiH ₄):
Used for depositing amorphous silicon, polycrystalline silicon, or silicon-based compounds (such as silicon nitride).
Typical process: Under low pressure (10-100 Pa), silane decomposes to generate silicon atoms, which react with nitrogen gas to form silicon nitride thin films for semiconductor insulation layers or optical coatings.
Silicon tetrachloride (SiCl ₄):
Suitable for high-temperature deposition of silicon-based materials, such as silicon carbide layers in the production of silicon carbide rods.
Nitrogen source gas
Ammonia gas (NH3):
Used for synthesizing nitrides such as gallium nitride and aluminum nitride.
Typical process: In MOCVD (Metal Organic Chemical Vapor Deposition), ammonia reacts with trimethyl gallium to form gallium nitride thin films, which are used for LED chip manufacturing.
Nitrogen (N ₂):
At high temperatures, it can react with metals to form nitrides, such as titanium nitride (TiN) coatings, which are used as wear-resistant layers for cutting tools.
Metal organic source gas
Trimethylaluminum (TMA, (CH ∝) ∝ Al):
Used for depositing aluminum oxide (Al ₂ O3) or aluminum based alloy thin films.
Typical process: In ALD (Atomic Layer Deposition), TMA and water vapor are alternately introduced to achieve single-layer alumina growth for high dielectric constant materials.
Trimethylgallium (TMG, (CH ∝) ∝ Ga):
Used for epitaxial growth of gallium nitride, it is a core material for LED and power electronic devices.
Hydrogen (H ₂)
Characteristics: Reductive gas that can remove surface oxides of substrates and promote reactions.
Application scenarios:
In semiconductor manufacturing, hydrogen is used to reduce the surface oxide layer of silicon and enhance the adhesion of thin films.
As an auxiliary gas for carbon source gas, such as in methane cracking, hydrogen can suppress carbon deposition and improve the quality of diamond films.

3. Doping gas: regulating the electrical properties of materials
Phosphine (PH ∝)
Characteristic: Provides phosphorus element for n-type doped silicon-based materials.
Application scenario: In solar cell manufacturing, phosphine doping can enhance the conductivity of silicon wafers and optimize cell efficiency.
Borane (B ₂ H ₆)
Characteristic: Provides boron element for p-type doped silicon-based materials.
Application scenario: In semiconductor devices, borane doping can form p-n junctions to achieve functions such as diodes and transistors.
Other doping gases
Such as arsine (AsH3), antimony hydride (SbH3), etc., used for doping specific semiconductor materials.

4. Special functional gases: meet specific process requirements
Oxygen (O ₂)
Characteristics: Oxidizing gas, can be used for oxidation reactions or surface treatment.
Application scenarios:
In optical thin film deposition, oxygen reacts with silane to form a silicon dioxide (SiO ₂) thin film, which is used as an anti reflective film or protective layer.
In metal surface oxidation treatment, oxygen can generate a dense oxide layer, enhancing corrosion resistance.
Water vapor (H ₂ O)
Characteristic: Provides oxygen element and participates in oxidation reactions.
Application scenarios:
In the ALD process, water vapor alternately reacts with metal organic sources (such as TMA) to achieve single-layer growth of aluminum oxide.
In the oxidation treatment of carbon materials, water vapor can regulate the degree of oxidation and prepare porous carbon structures.
Hydrogen chloride (HCl)
Characteristics: Corrosive gas, can be used for etching or surface cleaning.
Application scenarios:
In semiconductor manufacturing, hydrogen chloride etching can remove excess materials and define device structures.
In metal surface treatment, hydrogen chloride can remove the oxide layer and improve coating adhesion.

5. Key design of gas inlet system
Mass Flow Controller (MFC)
Accurately control gas flow rate (accuracy ± 0.5% FS) to ensure process repeatability.
For example, in gallium nitride epitaxial growth, the ammonia flow rate needs to be precisely controlled at 50-200 sccm to achieve a film thickness uniformity of ± 2%.
Gas mixing system
Support multi-channel gas pre mixing to avoid uneven local concentration.
For example, in silicon carbide deposition, silane and methane need to be mixed in a ratio of 1:4, and the mixing system can ensure a ratio accuracy of ± 1%.
Safety protection device
Equipped with gas leak sensors, automatic shut-off valves, and explosion-proof design to ensure safe operation.
For example, when hydrogen gas is introduced, the system automatically detects leaks and initiates emergency exhaust procedures.