Clean room facilities

The small geometrical features on a microchip necessitates the use of clean room facilities during the critical fabrication steps. Each cubic meter of air in ordinary laboratories may contain more than 107 particles with diameters larger than 500 nm. To avoid a huge flux of these ”large” particles down on the chips containing micro and nanostructures, micro and nanofabrication laboratories are placed in so-called clean rooms equipped with high-efficiency particulate air (HEPA) filtering system. Such systems can retain nearly all particles with diameters down to 300 nm. Clean rooms are classified according to the maximum number of particles per cubic foot larger than 500 nm. Usually a class-1000 or class-100 clean room is sufficient for microfabrication.The low particle concentration is ensured by keeping the air pressure inside the clean room slightly higher than the surroundings, and by combining the HEPA filter systemwith a laminar air flow system in the critical areas of the clean room. The latter system let the clean air enter from the perforated ceiling in a laminar flow and leave through the perforated floor. Moreover, all personnel in the clean room must be wearing a special suit covering the whole body to minimize the surprisingly huge emission of small particles from each person. The air flow inside the DANCHIP clean room is about 1.3x 10⁵ m³ h⁻¹, most of which is recirculated particle-free air from the clean room itself. However, since the exhaust air from equipment and fume hoods is not recirculated, there is in intake of fresh air of 0.3 x10⁵ m³ h⁻¹.