Minienvironments and thermal effects

Current trends in cleanroom technology are moving away from conventional systems and towards localized areas so-called minienvironments. To date, production facilities have been set up as ballrooms, clean-benches or minienvironments with a simple encapsulation, either in connection with a cleanroom ceiling or with their own air purification systems. The air filter technology available on the market today easily fulfills current requirements for eliminating particles. The encapsulation often consists of simple wall units with access for maintenance. However, optimal airflows and cleanliness around the substrate cannot be achieved using this method. All cleanliness relevant functional units must be considered as a whole "minienvironment system". Functional units are the surrounding cleanroom technology, the supply and removal of process media, process equipment, production and operational organization, e.g. substrate handling and the personnel employed. The minienvironment system should center on optimizing airflows around the substrate, thus fulfilling the highest cleanliness requirements possible. The aim of minienvironment technology is to provide a "substrate cleanroom" only in the immediate surroundings where the substrate requires the highest cleanliness conditions. One of the most important influences on the first airflow are thermal effects caused by, for example, hotplates. The thermals created by the hotplate directly affect the direction of the airflow in the minienvironment, and the stagnant zone above the hotplate increases. This paper considers minienvironments using a minimal cleanliness volume around the process chamber. The paper will provide information obtained from several experiments and their results. From the obstruction of airflows resulting from such items as hotplates, it has been possible to develop a method for designing minienvironment systems required to handle thermal problems.