Cleanrooms and equipment

Learn the basics of fab environments and equipment — cleanroom cleanliness, yellow rooms and FOUPs — through multiple-choice questions.

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Cleanrooms and equipment: key points

In semiconductor manufacturing even tiny particles can cause defects, so work is done in cleanrooms where airborne particles are kept extremely low. Cleanliness is expressed as the number of particles in a given volume of air.

In 300 mm fabs, wafers are carried automatically in sealed containers called FOUPs, and the usual approach is to keep only the inside of equipment at very high cleanliness.

All Cleanrooms and equipment questions (50)

  1. How is the cleanliness of a cleanroom generally expressed?
  2. What is the main reason yellow lighting is used in lithography areas?
  3. Which correctly describes a FOUP?
  4. What is the main purpose of the downflow method, in which air flows in one direction from ceiling to floor in a cleanroom?
  5. Which high-performance filters are used to remove fine particles from cleanroom air?
  6. What is the approach called that keeps only the small space around wafers at high cleanliness?
  7. What is the main reason the air pressure inside a cleanroom is kept higher than its surroundings (positive pressure)?
  8. Which is a major source of particles in cleanrooms, addressed by wearing cleanroom suits?
  9. Which term refers to gaseous contaminants (acids, bases, organics, etc.) rather than particles in a cleanroom?
  10. In 300 mm wafer fabs, which system automatically transports FOUPs between tools along rails on the ceiling?
  11. Which facility at a cleanroom entrance blows strong jets of clean air at workers to remove dust from the surface of their clothing?
  12. What is the main reason temperature is held extremely constant in cleanrooms, especially in exposure areas?
  13. What is used with precision equipment such as exposure tools to suppress the effects of vibration transmitted from the floor?
  14. Which device supplies ions to the air in a cleanroom to neutralize charge on wafers and equipment?
  15. Which unit at the front of process equipment opens FOUP doors and transfers wafers into the equipment while keeping them in a clean environment?
  16. Which correctly describes the properties required of cleanroom suits?
  17. Which device, arrayed on the ceiling, integrates a filter and fan to deliver clean air?
  18. Which is one correct reason for not letting cleanroom humidity become extremely low?
  19. Which items are strictly restricted from being brought into a cleanroom?
  20. Which correctly describes the typical approach to equipment layout in semiconductor fabs?
  21. What is the main purpose of replacing (purging) the inside of a FOUP with nitrogen?
  22. Which mini-environment method, widespread in the 200 mm era, carries cassettes in sealed pods and delivers them to equipment?
  23. In downflow cleanrooms, why are perforated floor panels (gratings) used?
  24. For process equipment using vacuum, which device treats exhaust gas containing harmful substances produced by reactions, tool by tool?
  25. Which equipment is installed in semiconductor fabs to prevent loss of wafers in process due to voltage sags or power outages?
  26. Which ISO 14644-1 cleanliness class corresponds to Class 100 of the former US federal standard (no more than 100 particles of 0.5 µm or larger per cubic foot)?
  27. What is a typical guideline for the air velocity blown from the ceiling in downflow cleanrooms?
  28. In bay-and-chase cleanrooms, how is the cleanliness of the maintenance space behind equipment (the chase) typically handled?
  29. Which element can be released from glass-fiber filters and similar sources and cause unintended doping (contamination) of wafers?
  30. Which is closest to the typical temperature setting of a cleanroom?
  31. Which instrument is used to measure the number and size of fine particles in cleanroom air?
  32. Which item, placed on the floor at cleanroom entrances and elsewhere, removes dust stuck to shoe soles?
  33. Which statement about the amount of particles shed by cleanroom workers is correct?
  34. As circuits are scaled down, how does the size of particles that must be controlled in the cleanroom change?
  35. What is the main reason wafers must not be touched with bare hands?
  36. Which statement about ISO 14644-1 cleanliness classes is correct?
  37. Which type of cleanroom blows clean air from parts of the ceiling and maintains cleanliness by mixing with and diluting the room air? Its cleanliness is lower than with unidirectional flow, but its equipment cost is lower.
  38. Which filter is used to remove airborne molecular contamination (AMC) such as ammonia and organics from cleanroom air?
  39. In cleanroom air conditioning, which unit filters outside air and adjusts its temperature and humidity before supplying it to the recirculating room air?
  40. In a fab's automated material handling system, which automated storage holds FOUPs temporarily until their next process step?
  41. In automated transport in a bay-type fab, which pair correctly names transport between bays and transport linking tools within a bay?
  42. Which cleanroom style places tools in a large room with few partitions, ensuring wafer cleanliness with sealed carriers such as FOUPs and mini-environments?
  43. In a high-cleanliness downflow cleanroom, which is closest to the typical number of times the room's air is replaced per hour (air changes per hour)?
  44. What is the main reason conductive (static-dissipative) materials are used for cleanroom floors and workbenches?
  45. Which is the common definition of HEPA filter performance?
  46. In exposure areas using chemically amplified resists, why are basic molecular contaminants such as ammonia and amines controlled especially strictly?
  47. In fabs, what is the main reason the inner surfaces of stainless steel pipes that supply high-purity gases are electropolished (EP)?
  48. What is the role of the thick concrete floor with a grid of holes (waffle slab) used in fab cleanrooms?
  49. In precision facilities such as fabs, which metric grades allowable floor vibration levels as vibration velocity per frequency band?
  50. When installing electron-beam lithography systems, electron microscopes and the like, which environmental factor needs special attention besides vibration?

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