Can custom PECVD electric furnaces be evacuated?

Customized PECVD electric furnaces usually have vacuum pumping function, which is one of the core conditions for realizing plasma enhanced chemical vapor deposition (PECVD) process. The following analysis will be conducted from four aspects: principles, equipment configuration, vacuum performance requirements, and selection suggestions:

1. The necessity of vacuum pumping: basic conditions for PECVD process
Plasma excitation demand
PECVD ionizes the reaction gas into plasma through radio frequency power supply, and the stable existence of the plasma needs to be achieved in a low-pressure environment (usually 1-1000Pa). If the furnace is at atmospheric pressure and the density of gas molecules is too high, it will make it difficult to maintain the plasma and affect the efficiency of thin film deposition.
Impurity control
The vacuum environment can significantly reduce the impurities such as oxygen and water vapor in the furnace, avoiding the oxidation or contamination of the film. For example, when depositing silicon nitride films, if the oxygen content in the furnace is too high, SiO ₓ N ᵧ impurity phases will be generated, which will reduce the insulation performance of the film.
Process repeatability guarantee
A stable vacuum degree can ensure consistent parameters such as gas partial pressure and plasma density for each process, thereby ensuring the repeatability of film thickness, composition, and performance.

2. Customized vacuum system configuration for PECVD electric furnace
Types and combinations of vacuum pumps
Dry pumps (such as screw pumps and molecular pumps): suitable for clean processes that require no oil pollution (such as semiconductors and photovoltaics), and can pump up to the level of 10 ⁻ Pa.
Oil sealed pump (such as rotary vane pump): Low cost, but requires regular oil change, which may introduce oil vapor pollution, suitable for scenarios with low cleanliness requirements.
Combination scheme: commonly known as “rotary vane pump+Roots pump” two-stage pumping, or “dry pump+molecular pump” high vacuum combination, balancing pumping speed and ultimate vacuum degree.
Automatic control: Set the target vacuum degree through PLC or touch screen, and the system automatically adjusts the valve opening and pump operation to achieve fast pumping and stable pressure control.
Gas path design
Independent gas path: The reaction gas, carrier gas, and doping gas need to be independently controlled to avoid cross contamination. For example, when depositing a-Si thin films, the SiH ₄ and H ₂ gas paths need to be completely isolated.
Quick switching valve: supports fast switching of multi gas processes, reduces vacuum pumping time, and improves production efficiency.

3. Clear vacuum performance parameters are required during customization
ultimate vacuum
Conventional requirement: The photovoltaic industry typically requires ≤ 5 × 10 ⁻ ³ Pa.
Selection criteria: Choose according to the cleanliness requirements of the process. The higher the ultimate vacuum degree, the higher the equipment cost and maintenance difficulty may increase.
pumping speed
Definition: The time required to reach the target vacuum level from atmospheric pressure within a unit of time. For example, it takes ≤ 5 minutes to pump from atmospheric pressure to 10 Pa.
Influencing factors: furnace volume, pump set pumping speed, gas path resistance, etc. Larger furnaces require pump sets with higher pumping speeds.
pressure stability
Process requirements: Pressure fluctuations during the deposition process must be ≤ ± 5%, otherwise it will cause changes in plasma density and affect the uniformity of the film.
Control measures: Adopting designs such as variable frequency pump units, pressure closed-loop control, and pneumatic buffer tanks.
leak rate
Indicator: The furnace leakage rate should be ≤ 1 × 10 ⁻⁹ Pa · m ³/s to prevent external gas from infiltrating and polluting the process environment.
Testing method: Before customization, the supplier is required to provide a helium mass spectrometry leak detection report.

4. Customized selection suggestions
Match according to process requirements
Photovoltaic industry: Choose a dry pump combination with a maximum vacuum degree of ≤ 5 × 10 ⁻ ³ Pa and moderate pumping speed, balancing cost and performance.
The semiconductor industry requires a vacuum degree (≤ 1 × 10 ⁻ ³ Pa) and lower leakage rate, which may require the configuration of molecular pumps and oxygen free copper sealing designs.
Research and development equipment: can reserve vacuum interfaces and support subsequent upgrades of high vacuum pump units.
Pay attention to maintenance convenience
Pump unit location: Preferably choose side mounted or buried pump units for easy maintenance and replacement.
Oil circuit design: If an oil sealed pump is selected, an oil mist filter and an automatic oil replenishment device need to be installed to reduce manual intervention.
Safety and Environmental Protection
Exhaust gas treatment: For toxic gases such as PH ∝ and B ₂ H ₆, exhaust gas combustion towers or wet scrubbing towers need to be installed to ensure emissions meet standards.
Anti backflow design: In the event of a sudden power outage, the air circuit should automatically close to prevent pump oil from being sucked back into the furnace.