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What is Cleanroom?

A room in which the number of airborne particles is kept below a specified level and temperature, humidity and pressure are also controlled. Semiconductor manufacturing takes place in cleanrooms so that wafers are not contaminated.

Read the beginner explainer: What Is a Cleanroom? Why Chip Fabs Fight Dust

Japanese name: クリーンルーム

Cleanroom appears in 36 practice questions across 4 topics, including Cleanrooms and equipment, Environment, health and safety, Oxidation and diffusion.

Field: Cleanrooms and equipment

What a cleanroom is

A cleanroom keeps the number of particles floating in its air below a specified level by continuously supplying filtered air and carrying contamination out of the room. In semiconductor manufacturing, a single particle about the size of a circuit feature landing on a wafer can make that chip fail. So air filtered through HEPA or ULPA filters in the ceiling is blown into the room, and temperature, humidity and room pressure are also held constant. The room is kept at a slightly higher pressure than its surroundings so that dirty air does not flow in.

Cleanliness classes

Cleanliness is expressed as the number of particles in a given volume of air, and the international standard ISO 14644-1 divides it into classes 1 to 9. The smaller the number, the cleaner the room; ISO Class 5 allows up to 100,000 particles of 0.1 µm or larger per cubic meter. This roughly corresponds to Class 100 of the withdrawn US Federal Standard 209E (100 particles of 0.5 µm or larger per cubic foot). Because people shed many particles, workers wear dedicated garments, masks and gloves and pass through an air shower before entering.

How a semiconductor fab cleanroom is built

In a typical fab, filtered air flows down from the entire ceiling (downflow), is drawn through a perforated floor into the space below, and is filtered again and recirculated. Leading-edge fabs do not make the whole building as clean as possible; instead, wafers travel in sealed containers called FOUPs on automated material handling systems (AMHS), and only the tool minienvironments are kept especially clean. This lets the bays where people work be held to a somewhat looser class and reduces the electricity needed to move huge volumes of air.

Try it: questions about Cleanroom

How is the cleanliness of a cleanroom generally expressed?

  1. ABy the number of particles above a certain size in a given volume of air
  2. BBy the room's temperature and humidity
  3. CBy the brightness of the lighting
Show answer and explanation

Answer: A. By the number of particles above a certain size in a given volume of air

Cleanroom cleanliness is expressed as the number of particles at or above a given size in a set volume of air. ISO 14644-1 defines Classes 1 through 9 by particles per cubic meter, with lower numbers being cleaner; Class 5 allows no more than 100,000 particles of 0.1 µm or larger per m³. Ordinary room air is around Class 9. Temperature, humidity and lighting are also controlled but are not cleanliness metrics.

What is the main purpose of the downflow method, in which air flows in one direction from ceiling to floor in a cleanroom?

  1. ATo quickly carry generated particles below the floor so they do not linger around wafers
  2. BTo raise the room temperature
  3. CTo lower noise in the room
Show answer and explanation

Answer: A. To quickly carry generated particles below the floor so they do not linger around wafers

Clean air from high-efficiency ceiling filters flowing uniformly downward carries particles from people and tools to the underfloor before they can rise, keeping them from lingering around wafers. It achieves higher cleanliness than mixing and diluting room air, but moving such large air volumes consumes much energy. Adjusting temperature or noise is not the purpose.

FAQ

Why do semiconductor fabs need cleanrooms?

When line widths are tens of nanometers or less, a single particle of similar size can cut or short a wire and make the chip fail. Besides particles, metals such as sodium and airborne molecular contamination (AMC) such as ammonia and organics also lower yield, so they are controlled too.

How are cleanroom classes defined?

ISO 14644-1 defines classes 1 to 9 by the maximum number of particles per cubic meter of air. For particles of 0.1 µm or larger, the limit for class N is 10 to the power N, so each step down in class is a factor of 10 cleaner. A class is stated together with the occupancy state in which it is measured: as-built, at-rest or operational.

Cleanroom in the explanations

Questions that mention Cleanroom (36)

  1. How is the cleanliness of a cleanroom generally expressed?
  2. What is the main purpose of the downflow method, in which air flows in one direction from ceiling to floor in a cleanroom?
  3. Which high-performance filters are used to remove fine particles from cleanroom air?
  4. What is the main reason the air pressure inside a cleanroom is kept higher than its surroundings (positive pressure)?
  5. Which is a major source of particles in cleanrooms, addressed by wearing cleanroom suits?
  6. Which term refers to gaseous contaminants (acids, bases, organics, etc.) rather than particles in a cleanroom?
  7. Which facility at a cleanroom entrance blows strong jets of clean air at workers to remove dust from the surface of their clothing?
  8. What is the main reason temperature is held extremely constant in cleanrooms, especially in exposure areas?
  9. Which device supplies ions to the air in a cleanroom to neutralize charge on wafers and equipment?
  10. Which correctly describes the properties required of cleanroom suits?
  11. Which is one correct reason for not letting cleanroom humidity become extremely low?
  12. Which items are strictly restricted from being brought into a cleanroom?
  13. In downflow cleanrooms, why are perforated floor panels (gratings) used?
  14. What is a typical guideline for the air velocity blown from the ceiling in downflow cleanrooms?
  15. In bay-and-chase cleanrooms, how is the cleanliness of the maintenance space behind equipment (the chase) typically handled?

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Comparisons that include this term

Related terms

Downflow Airborne molecular contamination (AMC) ESD (electrostatic discharge) Ultrapure water OHT (overhead hoist transport) ISO 14644-1 Overlay Mobile ions Threshold voltage Gettering

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