Clean room

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A clean room for the production of microsystems . The yellow lighting prevents unwanted exposure of photoresists for photolithography .
Clean room under construction for microelectronics production prior to the installation of manufacturing equipment. The clean room grid ceiling with filter fan units spans approx. 6,000 square meters and creates a clean room class of approx. ISO 3.
Entrance area of ​​a clean room
Clean room cabin for precision measurement technology

A pure or clean room is a room in which the concentration of airborne particles is very low.

Clean and ultra-clean rooms are required for special manufacturing processes - especially in semiconductor production -  where particles in normal ambient air would disrupt the structuring of integrated circuits in the range of fractions of a micrometer . Further applications of clean rooms or clean room technology can be found in optics and laser technology , aerospace technology, biosciences and medical research and treatment, research and aseptic production of food and drugs and in nanotechnology .

history

Presumably, medicine first recognized the need for a controlled environment and developed the classic operating theater in hospitals, obviously based on the black and white principle . There used to be industry-specific and regionally different requirements and standards for clean rooms, which have now been replaced by the uniform standard EN ISO 14644 .

functionality

A clean room is designed in such a way that the number of airborne particles that are brought into the room or arise there is as low as possible. Depending on the use, only the number of particles or the number of germs is monitored, as is necessary, for example, in the manufacture of pharmaceutical products . Other parameters such as temperature , humidity and pressure are usually also kept constant in order to create comparable conditions at all times.

In order to create the required conditions, various processes are used to prevent unwanted particles from getting into the air and to remove particles already in the air.

Since humans are usually the largest source of particles and other contamination, appropriate work clothing , special work equipment and tools, as well as the appropriate work technology, help to comply with the specified clean room class . For example, there are special lint-free clean room paper, clean room clothing , hoods and covers for shoes.

For clean rooms, such as those used in microelectronics, there are several hierarchical areas with the corresponding clean room class. The clean room (class ISO 4 and better), in which substrates are used, is surrounded by a separate area with the necessary equipment for coating and structuring. The pumps required for vacuum technology are usually located on a floor below.

The clean room access usually takes place via a sequence of different clean room areas with decreasing clean room class. There is usually a change of clothes between these areas. In order to minimize soiling of objects that come into contact with the floor (e.g. the soles of shoes), there are special sticky floor mats at the respective entrances. Access to the clean room itself is also via personnel and material locks, in which in turn strong air currents and filter systems whirl up and suck off existing particles, so that no additional contamination is brought in from outside.

In some clean rooms such as operating theaters, employees and visitors must undergo cleaning beforehand or at least put on protective clothing.

Materials that are used in clean rooms must have abrasion-resistant surfaces. Installed systems and devices may only minimally disturb the laminar air flow. Parts and machines that are to be brought into the clean room must be cleaned beforehand. As a rule, a clean room is subjected to overpressure ( overpressure ventilation ). In special cases, clean rooms are also operated with negative pressure , which prevents z. B. dangerous substances or pathogens can penetrate the outside.

So-called laminar flow units can also create workplaces with low levels of dust and particles, in which a cleaned, vertical or horizontal air flow and curtains ensure that the particle concentrations in the air and thus the particle deposits on the product are reduced.

The processes and types of air conditioning systems used are intended to ensure that contaminants are removed from the air immediately. A low-turbulence displacement flow ( laminar flow ) is used for this. The purity of the air is to be ensured together with a usually multi-stage filtering and a large air throughput.

Flow principles for clean rooms

Typical cleanroom headwear
Half man for the creation of a closed clean room area with personal access

A basic distinction is made between a turbulent dilution flow and a low-turbulence displacement flow:

  • In the case of turbulent dilution or mixed flow , the filtered clean air is introduced into the clean room in a turbulent manner (swirling) and creates a constant dilution of the particle concentration. The required clean room class is then maintained with clean room-friendly behavior of the staff. It is particularly important to ensure that objects and processes that generate particles are minimized in the clean room.
  • With the low- turbulence displacement flow , which is also known as “ laminar flow ”, the clean air flows into the clean room with low turbulence and usually vertically, and ensures that the sensitive work areas and machines are contaminated as little as possible. The air then escapes from the room on the opposite surface, usually through the perforated double floor, and is returned to the air circulation unit for repeated filtering .
Flow principle "turbulent clean room"
Flow principle "laminar flow clean room"

Clean room classes with values ​​of the particle concentration

Dependence of the permissible particle concentration on the particle size for different clean room classes. Size Digits: ISO, kl. Digits: STD209

In order to be able to operate a clean room, particle measurements must be carried out after construction and during operation . On the basis of these measurements, the cleanliness of the room can be classified according to a standard. For example, with class ISO 5 ( US old : class 100) max. 100 particles of min. 0.5 µm in diameter per cubic foot (3.5 particles per liter).

Industry-specific clean room definitions
Branch Major contamination Main norm
Semiconductor technology Particles US Federal Standard 209E, superseded by ISO 14644-1 and ISO 14644-2
European space technology Particles ECSS-Q-ST-70-01, based on ISO 14644
Food technology Microorganisms VDI 2083
pharmacy Germ count (KB) EU-GMP guidelines, Annex 1 Manufacture of sterile medicinal products
Clean room classes according to ISO 14644-1
  Particles per m 3
class ≥ 0.1 µm ≥ 0.2 µm ≥ 0.3 µm ≥ 0.5 µm ≥ 1.0 µm ≥ 5.0 µm
ISO 1 10          
ISO 2 100 24 10      
ISO 3 1,000 237 102 35    
ISO 4 10,000 2,370 1,020 352 83  
ISO 5 100,000 23,700 10,200 3,520 832  
ISO 6 1,000,000 237,000 102,000 35,200 8,320 293
ISO 7       352,000 83,200 2,930
ISO 8       3,520,000 832,000 29,300
ISO 9       35,200,000 8,320,000 293,000
Clean room classes according to GMP guidelines Annex 1
  Maximum number of particles allowed per m 3
class Rest state ≥ 0.5 µm Resting state ≥ 5 µm Operating condition ≥ 0.5 µm Operating condition ≥ 5 µm
A. 3,520 20th 3,520 20th
B. 3,520 29 352,000 2,900
C. 352,000 2,900 3,520,000 29,000
D. 3,520,000 29,000 not fixed not fixed
Clean room classes according to US FED STD 209E
  Particles per ft 3
class 0.1 µm 0.2 µm 0.3 µm 0.5 µm 5.0 µm
-
-
1 35 7th 3 1  
10 350 75 30th 10  
100   750 300 100  
1,000       1,000 7th
10,000       10,000 70
100,000       100,000 700
Note:
US FED STD 209E is no longer valid as of November 29, 2001.

Measurement regulations

With the revision of the standard in December 2015, the measurement regulations (measurement conditions) were also revised:

  1. The determination of the number of measuring points per room has been redefined. Previously defined as the root of the area as the minimum number of measurements, a minimum number of measuring points per area is specified in a table in the new version of December 2015.
  2. At the same time the statistical confidence interval fell away; instead, each measuring point should be considered individually: if the mean value of each measuring point is below the limit values, the measured room meets the requirements.
  3. When taking samples to determine the purity class in A areas (GMP), the hose length must be less than one meter.

See also

literature

  • Lothar Gail, Hans-Peter Hortig (Ed.): Clean room technology. 2. revised u. extended Edition. Springer, Berlin 2004, ISBN 978-3-540-20542-5 . (Overview of the development and practice of clean room technology)
  • Lothar Gail, Udo Gommel, Horst Weißsieker (eds.): Project planning for clean room technology. VDE Verlag, 2009, ISBN 978-3-7785-4004-6 . (Practical clean room knowledge)
  • Erwin Memmert: Clean room technology: Standards manual. Verlag Beuth, 2008, ISBN 978-3-410-16920-8 . (Standards manual on the subject of cleanrooms)
  • Win Labuda: Cleanroom consumables - aspects, simulation, arguments , special edition ReinRaumTechnik 01/2017 , Wiley-VCH Verlag, Weinheim
  • Win Labuda: On the history of pure work , ReinRaumTechnik 03/2018, Wiley-VCH Verlag, Weinheim

Web links

Commons : Cleanroom  - collection of pictures, videos and audio files
Wiktionary: Cleanroom  - explanations of meanings, word origins, synonyms, translations
  • Get Inside an Intel 45nm Chip Factory Channel Intel, YouTube, November 7, 2007, accessed on December 20, 2009 (Video about Intel's Fab32; The video shows, among other things, images from the clean room area of ​​a modern semiconductor production facility for microprocessors).

Individual evidence

  1. ↑ Definition & basics of the clean room. Retrieved April 8, 2016 .
  2. ↑ a b Notice of Cancellation of the GSA of November 29, 2001, reproduced on the IEST website ( Memento of September 28, 2011 in the Internet Archive ), accessed on June 23, 2008.
  3. ↑ ECSS-Q-ST-70-01C from ESA , accessed on February 4, 2016.
  4. ↑ a b Classification of the purity class according to GMP and EN ISO 14644-1 - Home
  5. ↑ a b c d e f Jürgen Blattner: Innovations in DIN EN ISO 14644-1: 2015 (changes with the new version from December 2015) ( Memento of the original from January 18, 2017 in the Internet Archive ) Info: The archive link became automatic used and not yet tested. Please check the original and archive link according to the instructions and then remove this notice. , gmp Verlag, accessed on January 18, 2017 @1@ 2Template: Webachiv / IABot / www.gmp-verlag.de