Calculation of Orifice Diameter for Flow Restrictor (OF) in a Semiconductor Vertical Furnace System

[Li Fei]

System Description:
This PID diagram is used in a vertical furnace system for semiconductor production equipment. The gas used is high-purity N₂, with an inlet pressure below 1 MPa. The system is designed to control the N₂ flow rate to 10 L/min. How can the orifice diameter of the flow restrictor (OF) be calculated?

 

[Snickster]

What is the purpose of the flow restrictor orifice? The flow controller controls the flow so why do you need a restriction orifice? Is it to limit the flow rate if the mass flow controller fails?

 

[Li Fei]

• Flow Limitation in Case of Regulator Failure:
  If the pressure regulator or flow controller fails (e.g., fails open), the flow restrictor acts as a physical limitation to prevent an excessive flow rate. This is critical in systems where safety, precision, and preventing overloading are essential.
• Downstream Pressure Stability:
  The orifice helps create a controlled pressure drop between the upstream regulator and downstream components, which stabilizes the pressure seen by the mass flow controller (MFC). Stable pressure at the MFC inlet is important for accurate and consistent flow measurements.
• Protection of Downstream Components:
  High-pressure surges, caused by upstream failures, can damage sensitive downstream components like MFCs, sensors, or process equipment. The flow restrictor mitigates such risks by inherently limiting flow to a design value.
• Safety Compliance:
  In industries like semiconductor manufacturing, redundancy and fail-safe designs are often required to comply with safety standards. The flow restrictor adds an extra layer of control to meet these requirements.
• Secondary Control for Specific Scenarios:
  In some systems, the flow restrictor might work in conjunction with the MFC to handle situations where the flow controller is unable to respond rapidly enough to certain fluctuations, ensuring smoother operation.

 

[Snickster]

This looks like a specialized flow control method for semiconductor manufacturing. I would contact manufacturer's representative for sizing information. Here is link below:

Mott Flow Restrictors for Efficient Semiconductor Manufacturing

New meta description: Explore Mott’s Precision Flow Restrictors for cost savings and improved safety in semiconductor manufacturing. Optimize your systems today!

mottcorp.com

 

[katmar]

I agree with Snickster that this is not a design to be performed from first principles. Whoever is putting the whole package together should have the necessary experience to specify the Restriction Orifice (RO).

But there are two points to take note of. The first is that it is meaningless to specify a gas flow unless the temperature and pressure at which the flow is measured are specified.

The second is that placing the RO downstream of the pressure regulator will reduce the accuracy of the mass flow controller. If the pressure at the inlet of the RO is held more-or-less constant by the pressure regulator the pressure drop through the RO and therefore also the inlet pressure to the mass flow controller will vary with changes in flow rate. Depending on the range of flows used in the process this may or may not be significant.

 

[pierreick]

Hi,
Another reference (in China):

Porous Metal Flow Restrictors - Filson Filters

www.filsonfilters.com

Pierre

 

[Li Fei]

Hi,
Another reference (in Chinna):

Porous Metal Flow Restrictors - Filson Filters

www.filsonfilters.com

Pierre

Hi Pierre,

Thank you for the reference. However, regarding products from China, especially in the semiconductor industry, there aren't many reliable brands from Henan that can meet the required standards.

Best regards,

LI Fei

 

[georgeverghese]

What is the max permissible safe flow for the downstream furnace ? It must be a lot more than 10litres/min. This higher flow would be the sizing basis for the OF.

Presume the MFC has inbuilt pressure and temperature compensation on detected flow to get the corrected mass flow. In any case, it may be better to install the OF downstream of the MFC.