Applications for Waste Gas Treatment Tools by DAS Environmental Expert
The production of high-tech products like microchips, photovoltaics modules, LEDs and flat screen displays is based on highly complex and multi-stage manufacturing processes. During some of the manufacturing steps, sensitive amounts of waste gas occur which require immediate and direct (point of use) treatment.
The abbreviation CVD stands for chemical vapour deposition. With this method, which is used in the semiconductor industry, for example, a thin layer is formed on the surface of a substrate by means of a chemical reaction from the gas phase. In this way, defined layers of different metals, silicon nitride, silicon oxide, or polysilicon are produced using CVD methods during chip manufacture. In doing this gaseous substances are used, some of which are toxic, flammable, explosive, or damaging to the environment. Typical gases here include silane, ammonia, TEOS, and nitrogen trifluoride. The latest DAS Environmental Expert GmbH product designed especially for purifying exhaust gases from CVD processes comes from the STYRAX® product family.
Metal-organic chemical vapour deposition is used for the production of thin layers by means of gas phase deposition on organometallic compounds. This so-called precursor is passed into the reaction chamber in the form of a gas, where it reacts with other substances and creates a solid layer on the heated substrate. MOCVD methods are used in the semiconductor industry, among other things, and for the manufacturing of light emitting diodes (LEDs), where hydrogen and ammonia typically have to be treated. DAS Environmental Expert GmbH has developed the LARCH point-of-use system especially for the disposal of large quantities of these process waste gases.
Transparent conducting oxides have gained vast economic importance in recent years. The translucent, thin layers are important constituents of flat panel displays and of thin film solar modules, for example. They are produced by thermal evaporation or by specific chemical vapour deposition methods. The large quantities of waste gases generated here can be treated by burner/scrubber technology, for example through the use of UPTIMUM, directly at the point of use.
During etching, material is removed from a surface using corrosive substances. The method is particularly used in the semiconductor industry and in the manufacture of micromechanical components, since it is characterised by extremely high precision. Structures which are not to be removed are protected from the chemical etching by a special photo-resist. Dry etching procedures such as plasma etching and reactive ion etching or wet chemical methods are used during chip production. The resulting gases (various fluorine compounds) can be treated safely using burner/scrubber technology from the ESCAPE product family, for example.
Epitaxy is used in the semiconductor industry to form high precision crystalline layers on a carrier substrate. They can be dosed with a high precision that is not achievable using conventional dosing methods, for example. They are also characterised by having extremely high purity. Layers of this type are produced using special chemical or physical vapour deposition methods, as well as mixed forms thereof, or by means of liquid phase epitaxy. Typical waste gases from this process include hydrogen, dichlorosilane and germane, which can be treated using the AQUABATE gas scrubber or STYRAX burner/scrubber technology.
Whenever the thin silicon wafer has been wetted with a liquid in the course of its processing, it must subsequently be dried. No residue can remain on the wafer surface, since this would cause damage during the subsequent stages of the process.
In integrated circuit manufacture, the wafer must be cleaned after certain stages of the process. This takes place in so-called “wet benches”. Depending on the type of contamination, different solutions are used here such as fresh water, acid and alkaline chemicals, and volatile solvents. The wafers are then dried free of residue. In order to clean 200 millimetre wafers, the entire cassette is immersed. Chip manufacturers use single wafer cleaning for 300 millimetre wafers. The individual wafers are rotated at high speed and then doused with the respective cleaning liquids. Detergent residue is present in the waste air from the wet bench - either from the vapour phase or in the form of droplets. With the SALIX wet scrubber, DAS Environmental Expert GmbH is providing a plant with which this contaminated air can be extracted and purified in an uncomplicated way.
VOC - Volatile Organic Compounds
Carbon-containing compounds that evaporate easily are known as volatile organic compounds. This means that they are partially already in gaseous form at room temperature. Substances such as this are used as additives in both the semiconductor and the solar industry. They often have an unpleasant smell, and are also frequently toxic and harmful to the environment.
VOC emissions can also cause considerable damage within the companies themselves: If volatile organic compounds condense in waste air systems, they can block pipelines. The condensate may also escape in the form of leaks, flow back into production, and start fires. To avoid such a hazard and reliably remove these hydrocarbons from waste air in production facilities, DAS Environmental Expert GmbH has developed the JUNIPER system.
Fine Dust Emissions - Air Purification
Many waste gas treatment processes require subsequent waste air purification for dust extraction. Fine dusts are difficult to treat because the tiny particles in the waste air pass through the wet scrubber or separator without being trapped in the scrubbing liquid. DAS Environmental Expert GmbH has developed the EDC electrostatic dust collector product line especially for dust such as this. The products are used in the semiconductor, solar and TFT industries.
Dust from waste gases are tiny solid particles that can be suspended in the air for long periods once they have been swirled up. Fine dust refers to extremely fine particles of suspended particulate matter. In addition to the pollutant content, the dust particle size is a particularly decisive factor with regard to potential health hazards caused by dust in waste air.
Particles with a diameter greater than ten micrometres are considered to be coarse dust, which can become trapped in nose hairs and the mucous membranes of the nose and pharynx. The so-called inhalable fine dust, however, can pass through the trachea and bronchi deep into the lungs. Fine dust is usually denoted by a particle size of less than ten micrometres (“PM10”). A dust fraction of less than 2.5 microns is known as fine dust. Ultrafine particles have a particle size of less than 0.1 micrometres.