Computational Fluid Dynamics (CFD) modelling and simulation are widely applied in semiconductor cleanrooms to optimise the design and operation of these critical environments.
Cleanrooms are essential in semiconductor manufacturing to maintain a controlled and contamination-free environment, ensuring the quality and reliability of semiconductor devices.
The placement of air diffusers and return vents can be optimised with CFD
CFD plays a crucial role in understanding and improving the airflow, temperature distribution, and particle transport within cleanrooms, whilst also providing insights into other crucial parameters.
This article illustrates how CFD is applied in semiconductor cleanroom environments.
Airflow analysis
By simulating the airflow patterns within cleanrooms, designers can verify that air flows from the top to bottom in a laminar fashion and recirculation flow is minimised, if not eliminated altogether.
In addition, understanding how air moves throughout the cleanroom environment allows designers to optimise the placement of air diffusers and return vents to ensure uniform air distribution.
CFD results also assist in evaluating the effectiveness of the ventilation system and identifying potential dead zones where air circulation may be inadequate.
Using the air flow profile obtained via CFD simulation, further CFD simulations which involve particles modelling and dispersion within the cleanroom environment can also be conducted.
CFD simulations can predict temperature distributions within the cleanroom
This is crucial to prevent the contamination of semiconductor wafers during the manufacturing process.
Designers use the results from CFD particles simulation to identify areas where particles may settle on the wafers and from here, develop strategies to mitigate contamination risks.
CFD simulation aids in optimising the placement of equipment and exhaust systems within the cleanroom. It ensures that exhaust systems effectively remove contaminants without creating turbulence that could disrupt the cleanroom environment.
Control of temperature and pressure
Semiconductor manufacturing processes often require precise temperature control and pressure.
CFD simulations can predict temperature distributions within the cleanroom, helping to design and optimise the heating, ventilation and air conditioning (HVAC) system to maintain a stable and uniform temperature throughout the cleanroom environment.
CFD modelling helps in designing and optimising the HVAC system to meet the specific requirements of the cleanroom.
CFD models are employed to simulate the combustion process
It assists in determining the appropriate air exchange rates, filter efficiencies and airflow patterns to achieve the desired cleanliness level.
In addition, maintaining specific pressure differentials between cleanroom areas is vital to prevent contaminants from entering sensitive zones.
CFD simulations help in understanding and optimising pressure differentials to ensure that clean air flows from cleaner to less clean areas.
Fire and smoke analysis
CFD is a powerful tool employed to simulate and analyse the behaviour of fire and smoke. This method provides valuable insights into fire dynamics, smoke propagation and the impact on occupant safety.
CFD models are employed to simulate the combustion process by solving the governing equations for fluid flow, heat transfer and combustion reactions.
This allows for the prediction of temperature distribution, flame characteristics and fire development over time. This is followed by the prediction of the dispersion of smoke within the cleanroom environment.
To simulate the propagation of smoke, the models consider factors such as buoyancy, air movement and temperature.
CFD is a powerful tool employed to simulate and analyse the behaviour of fire and smoke
Simulating smoke propagation provides insight into the potential hazards and optimisation of evacuation strategies.
The simulation of fire using CFD accounts for heat transfer mechanisms, including conduction, convection and radiation.
This helps in understanding how heat is transferred through different materials and surfaces, aiding in the assessment of structural integrity and fire spread.
From the simulation results, designers and engineers can ensure that structures meet the required safety standards and guidelines.
The visualisation and characterisation of fire and smoke using CFD allows in assessing the effectiveness of evacuation routes, identifying potential bottlenecks and optimising escape strategies to enhance occupant safety.
Before construction, CFD is employed in the design phase of cleanroom to assess fire safety measures
Before construction, CFD is employed in the design phase of cleanroom to assess fire safety measures.
It helps in evaluating the effectiveness of fire protection systems, such as sprinklers and smoke extraction systems and optimising their placement for maximum efficiency.
In addition, CFD allows for sensitivity analysis by examining the impact of various parameters, such as ventilation configurations, material properties and fire source characteristics.
This helps in identifying critical factors that influence fire behaviour and smoke propagation.
Carbon dioxide concentration analysis
CFD can also be used to model and analyse carbon dioxide (CO2) concentration in fire and smoke scenarios.
Understanding the distribution of CO2 is essential for assessing the potential impact on occupant safety, as high concentrations can lead to asphyxiation.
Simulating the concentration of CO2 during fire involve modelling the transport of various species, including CO2, within the fluid domain.
The model accounts for the movement of gases as they disperse and mix with the surrounding air.
Since CFD models take into account the interaction between smoke and CO2, the simulation results help in understanding how the movement of smoke affects the dispersion and distribution of CO2 within a space.
The CFD numerical model considers the effects of ventilation systems on the dispersion of CO2
This allows in predicting with great accuracy the spatial distribution of CO2 concentration.
The CFD numerical model considers the effects of ventilation systems on the dispersion of CO2.
It helps in evaluating the effectiveness of natural and mechanical ventilation strategies in reducing CO2 concentrations and improving air quality.
By analysing CO2 concentration patterns, CFD can assess potential occupant exposure levels during a fire event.
It was reported that a carbon dioxide level at 100,000 ppm was the atmospheric concentration immediately dangerous to personnel in the vicinity and that exposure to 100,000 ppm for only a few minutes may cause a loss of consciousness.
Thus, the information obtained through CFD simulation is crucial for designing evacuation routes, safe refuge areas and emergency response strategies.
After a fire incident, CFD can be employed to analyse the lingering effects
CFD analysis allows for the evaluation of mitigation measures, such as the use of smoke extraction systems (Desmoke), ventilation enhancements, or the deployment of gas suppression systems.
This helps in optimising these measures to minimise CO2 concentrations and improve overall safety. CFD results can be used to demonstrate compliance with safety regulations that specify acceptable levels of CO2 concentration during fire events.
This is particularly important for occupant safety and building code adherence.
After a fire incident, CFD can be employed to analyse the lingering effects, including CO2 concentrations.
This post-fire assessment aids in understanding the long-term impacts on indoor air quality and informs post-incident strategies.
Conclusion
We have invited Tan Inn Kok, Managing Director of ASTI, a Singapore-based main contractor that has successfully designed and built many semiconductor cleanrooms, to provide a conclusion to this article.
According to the Director, the semiconductor industry has experienced rapid growth in recent years, driven by the fast-paced evolution of technology, which has become essential in our daily lives.
The development and production space in the semiconductor industry, such as cleanrooms, have become more rapid and dynamic.
This post-fire assessment aids in understanding the long-term impacts on indoor air quality and informs post-incident strategies
As a result, most of our customers expect higher quality products with shorter delivery lead times.
Thus, the implementation of CFD in our design is crucial as it helps to reduce and eliminate unnecessary changes or errors during project execution.
From the customer’s perspective, this speeds up progress, whilst for builders like us, CFD helps to keep the project within budget whilst meeting requirements.
