Analysis of Core Requirements for Semiconductor Cleanrooms: Building a Solid Environmental Foundation for Chip Manufacturing
Unlike cleanrooms in general industries, semiconductor cleanrooms require a comprehensive, high-standard control system encompassing core dimensions such as microparticles, molecular contamination, temperature and humidity, static electricity, and vibration. This system must adapt to the needs of all scenarios, from mature to advanced processes (7nm/5nm/3nm). The following is a detailed analysis of the key requirements for semiconductor cleanrooms from these core dimensions.
I. Cleanliness Level: Ultimate Control of Microparticles
In semiconductor manufacturing, even particles as small as 0.1μm (only one-thousandth the diameter of a human hair) can cause short circuits on wafers, lithography deviations, and directly lead to chip scrap. Therefore, cleanliness level is a core indicator for semiconductor cleanrooms, strictly adhering to the ISO 14644-1 international standard, with 0.1μm particles as the core control target. This is far higher than the traditional industry standard of 0.5μm. The more advanced the process, the more stringent the cleanliness level requirements.
ISO levels 1-4 are designed for core production areas: ISO 1 is used for the most precise processes such as EUV lithography, with no more than 10 particles ≥0.1μm per cubic meter; ISO 2-3 are suitable for lithography, ion implantation, and 12-inch wafer core processes; ISO 4 is used for wafer cleaning and chemical mechanical polishing (CMP). ISO levels 5-7 are used for auxiliary areas, warehousing, equipment maintenance, and other non-core areas, meeting basic cleanliness requirements and preventing external contamination from entering the core production area.
II. Air Purification and Airflow Organization: Constructing a Disturbance-Free Clean Environment
The core of the air purification system in a semiconductor cleanroom is to achieve "no particles, no impurities, and no disturbance," ensuring that the air in the clean area meets standards through scientific airflow organization and multi-stage filtration.
Regarding airflow patterns, ISO 1-4 levels utilize a vertical unidirectional flow (laminar flow) design in the core area, with the top fully equipped with FFUs (fan filter units), controlling the air velocity at 0.45±0.1 m/s. Uniform return airflow from the floor forms a top-down clean airflow barrier, effectively removing fine particles from the air and preventing them from settling on the wafer surface. ISO 5-6 levels employ non-unidirectional flow (turbulent flow), achieving an air exchange rate of 200-500 times/hour, while ISO 7-8 levels achieve 50-150 air exchange rates/hour. High-frequency air exchange maintains the cleanliness of the area.
In terms of the filtration system, ULPA ultra-high efficiency filters are used at the terminal, achieving a filtration efficiency of ≥99.9995% for 0.12μm particles. The filter coverage rate in the core area is ≥80%. Fresh air undergoes three stages of treatment: pre-filter, medium-efficiency filter, and chemical filter, with a focus on controlling airborne molecular contamination (AMC) to prevent harmful gases from corroding the wafers and equipment. Meanwhile, gradient pressure control ensures a positive pressure of +15~30 Pa relative to the non-clean area in the clean zone, with a pressure gradient of ≥5~10 Pa from the high-cleanliness zone to the low-cleanliness zone. This prevents backflow of external contaminants and is equipped with an automatic monitoring and audible/visual alarm system to monitor pressure changes in real time.
III. Temperature and Humidity Accuracy: Millimeter-Level Stable Control
In semiconductor manufacturing, even minute fluctuations in temperature and humidity directly affect wafer deformation and lithography linewidth shifts, thus impacting chip performance. Therefore, semiconductor cleanrooms require extremely high precision in temperature and humidity control, far exceeding that of ordinary industrial scenarios.
For temperature control, the general production area is maintained at 22±1℃, while critical areas such as lithography and chip inspection require a temperature accuracy of 22±0.1℃~±0.5℃ to avoid process deviations caused by temperature drift. The humidity control standard is 45%±5% RH, with critical processes requiring ±1%~±3% RH. This effectively prevents static electricity generation and avoids wafer moisture absorption deformation and chemical corrosion, providing a stable environmental foundation for chip manufacturing.
IV. Aspect-Oriented Contamination (AMC) Control: An Essential Requirement for Advanced Processes
As chip manufacturing processes advance to 5nm and below, the impact of AMC on chips becomes increasingly significant, with control proving even more challenging than microparticle management. AMC primarily comprises four categories: acidic (HF, HCl), alkaline (NH3, amines), hydrocarbons (VOCs), and doped/metal ions (Na, Fe, Cu). These must be controlled at the ppb level (parts per billion), otherwise, wafer surface corrosion and oxidation will occur, affecting the chip's electrical performance.
To achieve effective AMC control, semiconductor cleanrooms must be equipped with dedicated chemical filters, utilize closed-loop pipelines to transport high-purity gases, and select low-emission, corrosion-resistant building and equipment materials to reduce molecular contamination at its source. Simultaneously, a real-time AMC monitoring system must be established to ensure contamination levels remain within standard ranges, meeting the demands of advanced semiconductor processes.
V. Electrostatic Discharge (ESD) and Vibration Control: Mitigating Hidden Risks
Electrostatic discharge (ESD) and vibration are two major hidden risks in semiconductor manufacturing. Although not directly visible, they can cause irreversible damage to precision chips and equipment. For anti-static control, the floor should be made of anti-static PVC or epoxy material, with a surface resistance controlled between 10⁶ and 10⁹ Ω; a copper foil grid grounding system should be installed, with a grounding resistance ≤1Ω; equipment and workbenches must be fully grounded with metal surfaces and equipped with anti-static work surfaces (surface resistance 10⁴ to 10⁶ Ω); personnel entering the clean area must wear full sets of anti-static cleanroom suits, gloves, and ankle bracelets; critical areas should be equipped with ion fans to completely eliminate static electricity accumulation and prevent electrostatic discharge from damaging chips or attracting microparticles.
For vibration control, in core areas such as lithography and chip inspection, vibration must be controlled between 1 and 5 μm/s (X/Y/Z axes). Precision equipment such as lithography machines must be equipped with independent vibration-isolated foundations and anti-micro-vibration structures, kept away from vibration sources such as pumps, fans, and traffic, to prevent lithography deviations and equipment accuracy degradation caused by vibration, ensuring the stability of chip manufacturing.
VI. Building Materials and Personnel/Materials Management: Eliminating Pollution at the Source
The management of building materials, personnel, and materials in semiconductor cleanrooms forms the first line of defense against pollution. The core principles are "low dust generation, easy cleaning, and no dead corners."
Regarding building materials, wall panels and ceilings utilize electrolytic steel plates, handmade rock wool cleanroom panels, and anti-static color steel plates. All corners are rounded and seamlessly sealed to avoid dust accumulation dead corners. Floors use seamless epoxy self-leveling flooring, anti-static PVC, or raised flooring, which are corrosion-resistant, seamless, and easy to clean. Doors and windows are airtight cleanroom doors and windows with double-layered observation windows, using stainless steel or aluminum alloy frames. The use of materials that easily generate dust (such as wood, gypsum board, and ordinary paint) is strictly prohibited.
Regarding personnel and material management, personnel entering the clean area must follow the procedure of "changing shoes → changing clothes → air shower (air velocity ≥20m/s, time 15~30s) → clean area," wearing a full set of bunny suits, masks, gloves, and goggles to prevent human-borne contamination. Materials must enter through pass-through windows or airlocks, undergoing UV disinfection and dust-free packaging. Bare-hand contact with wafers and precision components is prohibited to mitigate contamination risks at the source.
VII. Compliance Standards: Establishing a Solid Quality Bottom Line
The design, construction, and operation of semiconductor cleanrooms must strictly adhere to both international and domestic standards to ensure compliance and professionalism. International standards mainly include ISO 14644-1 (cleanliness levels), SEMI (Semiconductor Equipment and Materials Association) standards, and relevant ASTM standards. Domestic standards are based on GB 50472 "Design Code for Cleanrooms in the Electronic Industry," combined with GMP requirements, covering the entire process of design, construction, testing, and acceptance to ensure that all cleanroom indicators meet standards, providing a compliant and reliable environmental guarantee for chip manufacturing. In summary, the requirements for semiconductor cleanrooms revolve around three core aspects: "precise control, comprehensive contamination prevention, and stable reliability." This involves constructing a comprehensive environmental management system across multiple dimensions, including cleanliness, air purification, temperature and humidity, air quality control (AMC), anti-static properties, and vibration control. As a core component of the semiconductor industry, high-standard cleanrooms not only guarantee chip yield but also reflect a company's technological strength, helping semiconductor companies achieve breakthroughs in advanced processes and large-scale production.