EP68: Think Building a Cutting-Edge Chip Factory is Easy? Think Again. Here's the Dirty Truth Behind Clean Rooms
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Summary: In this episode, we discuss the critical role of cleanrooms in semiconductor manufacturing, emphasizing the need for stringent control over particles, temperature, humidity, and chemicals to prevent contamination. We outline the standards including ISO 14644-1 and ISO 14644-2 standards for cleanroom classification and maintenance, explaining how laminar airflow, HEPA/ULPA filtration, and meticulous personnel practices ensure a contamination-free environment. We further delves into the construction and maintenance of ISO Class 5 or better cleanrooms, outlining essential components like modular panels, sealed windows, pressurization, and high air change rates. We highlight the importance of routine monitoring, cleaning protocols, personnel training, and scheduled maintenance in preserving the cleanroom environment and ensuring the successful production of high-quality semiconductors. It really is not that easy to start up from scratch and designing, building and maintaining a clean room is just one part of the complexity of modern advanced semiconductor fabrication. Questions to consider as you read/listen: What are the essential components of a cleanroom environment and their role in the semiconductor manufacturing process? How do ISO 14644 standards impact the design, construction, and operation of semiconductor cleanrooms? What are the key challenges and considerations in maintaining the cleanliness and functionality of a cleanroom over time?

Long format:  Think Building a Cutting-Edge Chip Factory is Easy? Think Again. Here's the Dirty Truth Behind Clean Rooms

The news is full of countries stating that they are going to make semiconductors and fabricate them. Whether it is India or UAE or Germany or Italy or Vietnam. It is really not that simple.

So you want to make a cutting edge chip fabrication plant from scratch with no native experience? Good luck. Just one level of difficulty is in designing, constructing and maintaining a clean room. INTRODUCTION Cutting-edge semiconductor plants need clean rooms to prevent contamination during the production of microchips, which are incredibly sensitive to particles and impurities. Even a single dust particle or microscopic contaminant can cause defects in semiconductor chips, rendering them unusable or significantly reducing their performance and reliability. Here’s why clean rooms are essential: Particle Control: Semiconductor chips are made using processes that involve etching and layering at microscopic scales. Particles much smaller than a human hair can interfere with these processes, leading to malfunctions. Clean rooms keep airborne particles to a minimum to avoid contamination. Temperature and Humidity Regulation: Semiconductor manufacturing is extremely sensitive to changes in temperature and humidity, which can affect chemical reactions and the precision of lithography (the process of patterning circuits on chips). Clean rooms maintain strict environmental control to ensure consistent quality. Chemical Control: Many materials and chemicals used in semiconductor production are reactive. Clean rooms limit contaminants, including gases and ions, which could react with these chemicals and ruin the chips. Precision in Lithography: Advanced semiconductor chips are made at extremely small scales, with features as small as a few nanometers. For lithography to be precise, the environment needs to be tightly controlled, and vibrations must be minimized. Clean rooms help to provide these conditions. Yield Improvement: The production of semiconductor chips is complex, and defects are costly. Clean rooms help maximize the yield of usable chips per wafer by reducing defects, which is crucial given the high costs associated with semiconductor manufacturing. Clean rooms are classified by the number of particles they allow per cubic meter, with semiconductor fabs often requiring Class 1 or even stricter classifications, meaning they permit as few as one particle per cubic meter of air. These conditions are fundamental for producing the advanced technology found in modern electronics, where even minor defects are unacceptable. THE STANDARDS ISO 14644-1 and ISO 14644-2 are critical standards for defining and maintaining cleanroom environments, especially for industries like semiconductor manufacturing, where air purity is paramount to avoid contamination.  ISO 14644-1: Classification of Air Cleanliness by Particle Concentration ISO 14644-1 provides criteria for classifying the cleanliness of air in cleanrooms by measuring particle concentration. Semiconductor facilities commonly require an ISO Class 5 or lower environment, demanding stringent control of airborne particles, especially since microscopic contaminants can severely impact microchip functionality. For ISO Class 5, a cleanroom must have a maximum of 3,520 particles per cubic meter at a size of 0.5 microns or larger. This level of cleanliness ensures that the semiconductor manufacturing process remains largely free of particulates that could damage the delicate circuitry and photolithography patterns on silicon wafers. ISO 14644-2: Monitoring and Compliance Verification ISO 14644-2 complements ISO 14644-1 by providing guidelines for monitoring, verifying, and maintaining the cleanliness of the cleanroom environment over time. This standard specifies the testing frequency and protocols necessary to confirm continued compliance with the established cleanliness class, based on particle concentrations. For semiconductor cleanrooms, this monitoring process is critical due to the sensitivity of microelectronics to particulate contamination. Laminar Airflow in Semiconductor Cleanrooms Laminar airflow is essential in semiconductor cleanrooms to maintain cleanliness by ensuring a consistent, unidirectional flow of air, typically moving vertically from the ceiling to the floor. High-efficiency particulate air (HEPA) filters or ultra-low penetration air (ULPA) filters are often used to filter incoming air, ensuring only clean, particle-free air reaches sensitive areas. This airflow system helps sweep away contaminants generated by personnel or equipment, preventing particles from settling on wafers and equipment. Monitoring and Control Monitoring the cleanroom involves continuous particle counting and environmental control to detect deviations from cleanliness standards. Advanced monitoring systems are used to detect particle concentration, humidity, and temperature. Semiconductor cleanrooms often have real-time particle counters, which are strategically placed to alert personnel to any increase in particle concentration immediately. This ongoing monitoring is vital for maintaining compliance with ISO standards and detecting any potential contamination risks promptly. Cleanroom Suits and Personnel Training Personnel working in semiconductor cleanrooms wear specialized cleanroom suits, which cover their entire body, including gloves, masks, and sometimes face shields. These garments are designed to contain human-generated particles such as skin flakes, hair, and other contaminants. The suits are made from materials that do not generate lint or static and are typically reusable after decontamination. Proper training of personnel is another critical aspect of maintaining an ISO Class 5 environment. Staff must be trained on correct gowning procedures, handling of cleanroom equipment, and movement techniques within the cleanroom. Even minimal movement can disturb airflow and release contaminants, so personnel are trained to minimize unnecessary motion. They also learn protocols for entering and exiting the cleanroom to prevent cross-contamination from external areas. Constructing and maintaining ISO Class 5 or better cleanrooms for semiconductor manufacturing requires careful design and rigorous protocols to control particulate contamination. Here’s a breakdown of the key components and practices: Construction of ISO Class 5 or Better Cleanrooms Room Design and Layout

Modular Panels and Seals: Walls, floors, and ceilings are made from non-shedding, easily cleanable materials, often prefabricated modular panels that are smooth, sealed, and designed to prevent particle accumulation. Sealed Windows and Doors: Cleanrooms have airtight windows, limited entry points, and doors with airlocks to maintain pressure control and minimize the chance of outside contaminants entering. Pressurization: Higher air pressure inside the cleanroom than in adjacent spaces prevents unfiltered air from entering. Positive pressure keeps airborne particles from infiltrating the cleanroom environment.

Filtration Systems and HVAC

HEPA/ULPA Filters: High-efficiency particulate air (HEPA) filters or ultra-low penetration air (ULPA) filters remove 99.99% of particles down to 0.3 microns. These filters are typically installed in the ceiling to facilitate laminar airflow. Laminar Flow Design: A unidirectional, vertical airflow pushes particles down and out of the room. This reduces the likelihood of particles settling on sensitive equipment. Return Air Vents: Vents are positioned near the floor to allow filtered air to exit, drawing contaminants out of the environment.

Flooring and Surfaces

Antistatic, Smooth Flooring: Flooring is typically made of seamless vinyl or epoxy, reducing particle generation and making surfaces easy to clean. Floors are often conductive to prevent static build-up, which can attract particles. Rounded Corners and Coved Floors: Corners are rounded, and wall-floor junctions are coved to eliminate particle traps, facilitating thorough cleaning.

Airflow and Ventilation Rates

High Air Change Rates: ISO Class 5 cleanrooms require around 240-600 air changes per hour. This high turnover rate keeps particulate levels low. Temperature and Humidity Control: Precise control of temperature and humidity prevents static electricity buildup and reduces particle generation, which is especially crucial in semiconductor manufacturing.

Maintenance of ISO Class 5 or Better Cleanrooms Routine Monitoring and Testing

Particle Counting: Continuous or periodic particle counting is performed to ensure compliance with ISO Class 5 standards. Real-time monitors detect changes in particulate levels, alerting staff to any potential contamination. Environmental Monitoring: Humidity, temperature, and pressure levels are continually monitored, as these factors influence particle behavior and static accumulation.

Cleaning Protocols

Regular Cleaning Cycles: All surfaces, including walls, floors, and equipment, are frequently cleaned using lint-free wipes, HEPA-filtered vacuums, and approved cleaning solutions. Minimizing Surface Contact: Equipment and work surfaces are minimized and specifically arranged to reduce particle generation. Cleaning of Equipment and Instruments: Equipment is cleaned to prevent particles from being reintroduced into the cleanroom. Some tools are kept in isolated spaces or mini-environments with even stricter cleanliness controls.

Personnel and Equipment Control

Gowning and De-Gowning Procedures: Personnel wear full cleanroom suits, gloves, masks, and eye protection, all of which are donned in designated gowning rooms. These garments prevent human-generated particles (skin flakes, hair) from contaminating the environment. Training and Compliance: Personnel are trained on proper entry, exit, and movement protocols to avoid disrupting airflow. Training emphasizes minimal movement and strict adherence to cleanroom practices. Use of Pass-Through Chambers: Materials and equipment enter through specialized pass-through chambers, minimizing door openings and reducing contamination risk.

Scheduled Maintenance and Filter Replacement

Filter Replacement and Testing: HEPA or ULPA filters require regular inspection and replacement to maintain optimal filtration efficiency. Pressure Differential Verification: Air pressure differentials are regularly tested to ensure positive pressure is maintained, which prevents external air from entering.

Routine Certification and Compliance Audits

Periodic Recertification: Cleanrooms are recertified periodically to ensure they meet ISO 14644-1 standards. This includes particle counting and full-system inspections. Audits and Process Reviews: Regular audits and process reviews help identify areas for improvement in maintenance and operations, ensuring the cleanroom remains compliant over time.

Through these construction and maintenance practices, ISO Class 5 cleanrooms are built and preserved to meet the stringent cleanliness standards needed for semiconductor manufacturing. Conclusion ISO 14644-1 and ISO 14644-2 establish the standards and protocols for cleanroom classification, monitoring, and compliance verification, ensuring that semiconductor facilities can achieve and maintain the required level of air cleanliness. Laminar airflow, continuous monitoring, cleanroom suits, and personnel training are all integral to meeting these stringent standards and preventing contamination, which is critical to the high-precision semiconductor manufacturing process. Sources:

Cleanrooms for Semiconductor Fabrication Plants: A Comprehensive Guide to Design, Construction, and Operation by Charles Nehme Clean Room Design Minimizing Contamination Through Proper Design By Bengt Ljungqvist, Berit Reinmuller Cleanroom Technology: Fundamentals of Design, Testing and Operation by William Whyte Jr. Semiconductor Microchips and Fabrication: A Practical Guide to Theory and Manufacturing 1st Edition by Yaguang Lian Get full access to GeopoliticsUnplugged Substack at geopoliticsunplugged.substack.com/subscribe)