What gases can be supplied to a customized PECVD electric furnace?

When customizing a PECVD (plasma enhanced chemical vapor deposition) electric furnace, the type of gas that can be introduced needs to be selected comprehensively based on the deposition material, process requirements, and equipment compatibility. The following are common gas classifications and their application scenarios, covering key considerations when customizing:

1. Common gas types and functions of PECVD electric furnace
a. Reactive gas (source of core deposition material)
Silicon based gas:
Silane (SiH ₄): Deposition of amorphous silicon (a-Si) and microcrystalline silicon thin films, used in solar cells and thin film transistors (TFTs).
Silicon tetrachloride (SiCl ₄): Decomposes and deposits silicon-based thin films at high temperatures, suitable for specific high-temperature resistant scenarios.
Nitrogen based gas:
Ammonia gas (NH3): co deposited with silane to form silicon nitride (Si3N4) as an anti reflection layer or insulating layer (photovoltaic, semiconductor).
Nitrogen (N ₂): used as a carrier gas or diluent gas to regulate the reaction rate.
Carbon based gas:
Methane (CH ₄): Deposition of diamond-like carbon (DLC) thin films for wear-resistant coatings.
Acetylene (C ₂ H ₂): decomposes and deposits carbon films at high temperatures, suitable for electrode materials.
Oxygen based gas:
Nitrous oxide (N ₂ O): co deposited with silane to form silicon oxide (SiO ₂) as an insulating or protective layer.
Oxygen (O ₂): assists in oxidation reactions and regulates film composition.
b. Carrier gas and diluent gas (adjust reaction atmosphere)
Hydrogen (H ₂):
As a reducing carrier gas, it promotes the decomposition of silane and increases the deposition rate.
Dilute highly reactive gases (such as SiH ₄) to prevent local overreaction.
Argon (Ar):
Inert carrier gas, suitable for hydrogen sensitive processes such as certain metal deposition.
Used for plasma excitation to enhance reaction activity.
Helium (He):
High thermal conductivity carrier gas, suitable for processes that require rapid heat transfer (such as ultra-thin film deposition).
c. Doping gas (regulating the electrical properties of thin films)
Phosphine (PH ∝):
Incorporating phosphorus elements to form n-type semiconductor thin films (such as n-type silicon).
Borane (B ₂ H ₆):
Doping boron elements to form p-type semiconductor thin films (such as p-type silicon).
Other doping gases:
Such as AsH3 (arsine), SbH3 (antimonide), etc., used for doping specific semiconductor materials.
d. Special functional gases
Fluorinated gases (CF ₄, SF ₆):
Used for etching or cleaning residues inside the furnace, but attention should be paid to corrosiveness.
Water vapor (H ₂ O):
Participate in oxidation reactions and deposit hydroxylated films (such as biomedical coatings).

2. Gas selection principles for customizing PECVD electric furnaces
a. Matching of process objectives
Film type: Select the reaction gas combination based on the target film (such as Si ∝ N ₄, SiO ₂, a-Si).
Example: Deposition of silicon nitride requires SiH ₄+NH ∝; Deposition of silicon oxide requires SiH ₄+N ₂ O.
Electrical properties: If doping is required, doping gases such as PH ∝ or B ₂ H ₆ need to be added.
b. Device compatibility
Gas purity:
The reaction gas needs to have high purity (≥ 99.995%) to avoid impurities contaminating the film.
The purity of the carrier gas (such as H ₂, Ar) should be ≥ 99.999% to prevent the introduction of oxygen or moisture.
Gas supply system:
An independent gas path needs to be configured to prevent gas cross contamination.
Corrosive gases (such as CF ₄) require the use of special pipeline materials (such as Hastelloy).
Safety design:
Toxic gases (such as PH ∝, B ₂ H ₆) need to be equipped with leak detection and automatic shut-off devices.
Flammable gases (such as H ₂, SiH ₄) require explosion-proof design, such as inert gas protection.
c. Balance cost and efficiency
Gas consumption:
Optimize the gas flow ratio to reduce waste (e.g. SiH ₄: NH ∝=1:3~5).
Recycling:
A recovery system can be designed for expensive gases such as SiH ₄ to reduce operating costs.

3. Key considerations when customizing
Gas pipeline design:
Independent gas path: Reaction gas, carrier gas, and doping gas need to be controlled separately to avoid cross contamination.
Quick switching valve: supports multi gas process switching, improving production flexibility.
Accuracy of Mass Flow Controller (MFC):
Selecting high-precision MFC (± 1% FS) ensures stable gas flow and directly affects the uniformity of the film.
Exhaust gas treatment system:
Configure a combustion tower or wet scrubbing tower to treat toxic gases (such as SiH ₄, PH ∝) in compliance with environmental requirements.
Safety interlock mechanism:
Automatically shut off the gas source, start the exhaust system, and trigger an alarm in case of gas leakage.
Process database support:
Customized equipment can pre store common process gas parameters (such as flow rate, pressure, time), simplifying the operation process.