Cerberus® Fire protection concept for the semiconductor industry Protecting fabrication plants and associated areas Application guide Fire & Security Products Siemens Building Technologies Group
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1 1.1 1.2 1.3 1.4 1.5 Fire protection concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Our aim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Facts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Why these high costs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
II Siemens Building Technologies Cerberus Division 01.
1 Fire protection concept 1.1 Our aim The early detection of incipient fire in clean rooms and in the related utility installations for the safety of personnel and to limit damage. A clean room is an area in a company where strict air cleanliness standards are maintained. A fire in such an area can cause major economic damage.
1.3 Why these high costs? D Even the slightest contamination can endanger processes and destroy an entire production lot. D Clean room systems must be continuously in operation. That means overpressure or underpressure must be maintained at all times and this includes air recirculation and air filtering. A breakdown can have catastrophic consequences for production. D Even small fires can cause smoke and corrosion damage. D Following contamination, the clean room must be painstakingly cleaned.
2 An introduction to clean room technology Clean room technology protects products, processes and the workforce from the harmful influence of contamination in a clean workplace.
3 Detailed planning of fire detection systems 3.1 Aim The early detection of incipient fire in clean rooms and in the related utility installations to limit damage. The prevention of false alarms through the use of suitable and tested fire detectors. 3.2 Critical aspects of planning to be taken into account The purpose of clean room technology is to maintain a predetermined level of air cleanliness. This is achieved by an appropriate choice of air handling concepts.
Fire aerosols versus airflow Fire aerosols which arise in a clean room are comparable with airborne foreign particles. Depending on the size and type of fire, they are diluted by the powerful air flow and immediately swept away Detectors on the ceiling Conventional fire detection systems with detectors on the ceiling are only suitable for the early detection of incipient fires in clean rooms in areas of non-unidirectional airflow with 10 – 50 changes of air/h.
3.4 Concept for fire detection Basic concept for • Clean room monitoring – High sensitivity air sampling smoke detection system with HSD detectors For early fire detection through the monitoring of extract air from the clean room. – and additional MB2 detector boxes with DO1153 The MB2s automatically alert the fire department in the second alarm stage – DO...
Detector siting – High sensitivity air sampling smoke detection system with HSD detectors and additional MB2 detector boxes MB2 with DO1153 Plan and site the tube system taking into account the air handling system. See the following planning examples, section 4 For maintenance reasons the HSD detectors must be sited in the service area of the clean room. Air recycling is important, i.e. the air sampled via a tube system must be taken back to the area with the same air pressure.
3.5 Stages in the planning of a fire detection system Production processes in the semiconductor industry are highly specialized and adjusted to current products. Each factory looks different and has a different environment. Our recommendations are therefore of a general nature. However, with the detailed information on clean room technology, the planning engineer should be able to work out his own concepts and solutions.
D Working conditions are rendered much more difficult. The stages of work must be planned and prepared down to the last detail with the customer’s personnel. D It may be necessary to use special wiring and installation material D Time-consuming arrangements have to be made if the customer requests acceptance test fires. D etc.
4 Planning examples The first planning example shows a factory for watch microelectronics. Here so-called „linear protection” is used for the clean room protection concept . We talk of linear protection if a clean room conditions have to be provided for a row of adjacent workplaces. A common application of this principle is the „clean tunnel” which is often found in the microelectronics field (see also 4.1.2). The second example shows a spacious microchip factory.
4.1.2 Air handling principle at the workplace Here the clean room is divided into various air cleanliness zones according to the processing and circulation zones. For certain workplaces, air cleanliness class 1000 is inadequate. Frequently the so-called tunnel principle is used for the organization of adjacent workplaces with air cleanliness classes 1 or 10. In such a case, partitions are installed between the critical work areas and the surrounding areas.
4.1.4 Air sampling smoke detection system concept In this situation the best location for an air sampling smoke detection system is the service area through which the air from the clean room blows before it is taken back to the air purification system. The ideal location for the detection of fire aerosols from the clean room would be the extract air vents at floor level where the air from the clean room flows into the service area.
Clean room type A, 1st example 4.2.1 A cleanroom with axial air circulation fans installed sideways connecting the supply-air plenum (dropped ceiling) at the top and the return-air plenum (raised floor) at the bottom. Air treatment floor 3rd floor Height 5.5m Dropped ceiling Height: 5m Cleanroom 2nd floor ÙÙÙÙ ÑÑ ÑÑÑÑÑÑ ÙÙÙÙ ÓÓÓÓÓÓÓÓ ÙÙ ÔÔÔÔÔÔÔÔ ÙÙ ÙÙ Height: 3.4m A Raised floor Height: 2m A Utilities distribution area 1st floor Height: 3.
Details on the planning of the fire detection systems Clean room on 2nd floor Length 55m Width 50m Area 2750m2 Height 3.4m High sensitivity air sampling smoke detection system with HSD detectors in a 2m high raised floor: – 6 or 12 BDH 2450.1 detection devices with interface card BDC2400 (pre-alarm 15%, Alarm 30%) – 6 AD2 active detectors Air sampling tubes: – 2 air sampling tubes mounted parallel in 2 metre high raised floor; first tube 1.25m above the floor, second tube 1.
4.2.2 Clean room type B, 2nd example A cleanroom with filter fan units installed in the dropped ceiling connecting the supply-air plenum (dropped ceiling) at the top and the return-air plenum (raised floor) at the bottom. Air handling system Air circulation fans: Output per unit: Total output: Siting: Dropped ceiling Height: 0.6m Cleanroom 2nd floor Height: 3.4m 1300 units 800m3/h 1,040,000m3/h in the dropped ceiling ÑÑ ÑÑÑÑ Ñ A Raised floor ÓÓÓÓÓÓÓÓÓ Height: 0.8m A 50m Fig.
Details on the planning of the fire detection systems Clean room, 2nd floor Length 55m Width 50m Area 2750m2 Height 3.4m High sensitivity air sampling smoke detection system with HSD detectors in an 0.8m high raised floor. – 10 BDH2450.1 detection devices with interface card BDC 2400 (pre-alarm 15%, alarm 30%) – 10 AD2 active detectors Air sampling tube: – 1 air sampling tube installed in the 0.8m high raised floor, 0.
Clean room type B, 3rd example 4.2.3 A cleanroom with air circulation fans installed in the dropped ceiling connecting the supplyair plenum (dropped ceiling) at the top and the return-air plenum (raised floor) at the bottom. Air handling system Air circulation fans: Output per unit: Total output: Siting: Dropped ceiling Height 1.95m Cleanroom 2nd floor Height: 3.4m 500 units 800m3/h 410,000m3/h in the dropped ceiling ÑÑ ÑÑÑÑÑÑ ÓÓÓÓÓÓÓÓÓ A Raised floor Height 0.55m A 22m Fig.
Details on the planning of the fire detection systems Clean room, 2nd floor Length 86m Width 22m Area 1892m2 Height 3.4m High sensitivity air sampling smoke detection system with HSD detectors in an 0.55m high raised floor. – 14 BDH2450.1 detection devices with interface card BDC 2400 (pre-alarm 15%, alarm 30%) – 14 AD2 active detectors Air sampling tube: – Air sampling tube mounted at 30cm above the floor in the 0.55m high raised floor.
4.2.4 Clean room type B, 4th example A cleanroom with filter fan units installed in the dropped ceiling connecting the supply-air plenum (dropped ceiling) at the top and the return-air sideways. Air handling system Air circulation fans: Output per unit: Total output: Siting: Dropped ceiling Height: 1.50m Cleanroom 2nd floor Height: 2.9m 320 units 920m3/h 294,400m3/h in the dropped ceiling ÑÑÑÑ ÑÑÑÑ A A Fig.
Details on the planning of the fire detection systems Clean room, 2nd floor Length 62m Width 36m Area 2232m2 Height 2.9m High sensitivity air sampling smoke detection system with HSD detectors at the return air outlets slightly above floor level: – 10 BDH2450.
5 Information on microchip production 5.1 Introduction into the semiconductor industry The semiconductor industry has its roots in the 1947 discovery of the transistor. Integrating electronics into every aspect of life has provided the impetus for the development of cheaper and yet more powerful devices. Progress has continued at an accelerated pace from discrete transistors, operational amplifiers through to the modern microprocessor. In 1995 total sales of semiconductors reached US$140 billion.
Masking Different parts of the wafer are processed at different times. Areas of the wafer are masked using either a photoresistive or light-sensitive film. This creates a surface similar to photographic paper. Masks are then precisely applied and aligned to allow the layout of the integrated circuits to be located on the wafer. Using a photo-lithographic process, an intense light beam exposes the sensitive areas of the mask. Etching Unwanted photo-resist material is removed using various chemicals.
6 Detailed information on clean room technology 6.1 Flow control in the clean room The sources of particulate air contamination in workrooms are D the outside air D the air handling systems and D the release of particles in the workrooms themselves (e.g. through work processes, personnel, expendable material, cleaning agents, maintenance work etc.
6.1.2 Unidirectional airflow If the demand is for higher and the highest level of air cleanliness, we apply the principle of unidirectional airflow, as it is called. In everyday language it is also known as laminar flow although it is not quite physically correct. With this method, the contaminated air released in the room is carried away by the shortest route and so rendered harmless.
Fig. 14 and Fig. 15 show clean room variations with unidirectional airflow directed vertically downwards and Fig. 16 with unidirectional airflow directed horizontally (laminar flow). Another variant with so-called filter-fan units is gaining increasing importance. With this system, the filters can be exchanged more easily and safely. The overpressure in the clean room ensures that falling dust particles cannot reach the clean room. The concept with filter fan units offers better and greater flexibility.
6.2 Air change Air cleanliness class Number of air changes per hour (approx.) 10,000 15 – 30 1,000 20 – 60 100 70 – 300 10 and 1 600 – 700 To achieve the required air cleanliness class for new products, e.g. 16 Mbit DRAM, process-controlled equipment is placed in so-called „mini-environments”. Only in these minienvironments is the highest air cleanliness class maintained, e.g. class 1 means that in a cube of air with sides 30 cm long, only one 0.5µm3 particle is accepted.
6.5 Operating mode of air handling systems 6.5.1 Continuous operation Normally, clean room systems are continuously in operation, even outside working hours. The flow control principle must be guaranteed at all times. However, it is often switched to half power, e.g. with unidirectional airflow, at approx. 0.2m/s. 6.6 Air cleanliness classes There are various national standards and guidelines with corresponding air cleanliness classes for the assessment of the cleanliness of room air.
ISO/DIS 14644-1 Draft International Standard This standard will supersede the various national standards. The work is at an advanced stage worldwide and and is about to be approved by the International and European standards committees ISO and CEN. Air cleanliness class Particle size in µm Maximum concentration value per m3 air N ≥ 0.1 µm ≥ 0.2 µm ISO 1 10 2 ISO 2 100 ISO 3 ≥ 0.3 µm ≥ 0.
7 Dangerous chemicals and gases 7.
Gas Formula Comments / Hazards Phosphorous Pentafluoride PF5 – toxic – corrosive – oxidizing gas Silane SiH4 – very toxic – spontaneously flammable in air Tetrachlorosilane SiCL4 – corrosive – react violently if mixed with water Silicon Tetrafluoride SiF4 – toxic – corrosive Tungsten Hexafluoride WF6 – toxic – corrosive 7.
7.
8 Terms, Definitions Airborne contamination Contamination of the air due to particles. Airlock Room with mutually bolted doors between two or more rooms of different cleanliness classes or different pressure levels. It may be designed for the movement of personnel or material. Changing rooms Rooms to change clothes before entering or leaving clean rooms and/or aseptic areas.
Particulate concentration Number of particles per volume of air (particles/m3) determined by the respective measuring technique. SMIF-box Standard Mechanical Inter-Face for the transport of wafers from one work station to another, thus avoiding the exposure of the wafers to room atmosphere. 9 D D D D Bibliography The Fundamentals of Clean room Design. Dr.
Keyword index A F Acids, 1 Air cleanliness class, 23, 26, 27, 28 Air supply, 23 Airborne contamination, 32 Airlock, 32 Alerting of the works fire brigade, 2 Average amount, 1 Film deposition, 21 Filter fan unit, 6, 15, 19, 25 Filtering the air for floating particles, 23 Fire aerosols, 12 Fire aerosols versus airflow, 5 Fire protection of wet benches, 8 Fires in clean rooms, 1 First air, 32 Floating particle filter, 23 B Basic concept for clean room monitoring, 6 C Causes of fire, 2 Changing rooms, 32 C
O Overpressure, 3, 26 P Particle, 32 Particle size, 28, 32 Particulate concentration, 33 Particulate contamination, 32 Passivation, 22 Point-type smoke detector, 11 Polishing, 21 Pressure differences between adjacent workrooms, 5 Protection concept, 1 S Semiconductor industry, 21 Silane, 1 SMIF-box, 33 Smoke and corrosion damage, 2 Smoke generator, 7 Solvents, 1 Supporting measures, 7 T Test fires, 7 with metal film resistors, 7, 14, 16, 18, 20 with smoke sticks, 7 U Underpressure, 3, 26 Unidirectional
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