COVERSTORY
several technologies, DAS decided to build on its semiconductor experience with Burn / Wet systems. The existing systems were scaled up and modified to cope with the particular demands of the PV process tools. While a thermal/wet treatment only heats the gases electrically and requires the addition of an oxident, burn/wet technology requires a fuel gas for the abatement process. In the combustion chamber various reactions take place including oxidation, reduction and pyrolysis. Gaseous and solid compounds generated by
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combustion are absorbed or suspended in a scrubbing liquid. Combustion reaction products are typically acidic, are immediately quenched on contact with the cool scrubbing liquid and so prevent any recombination into dangerous species. The waste products produced in combustion processes are scrubbed and neutralized instantly using a water and lye mixture.
The combustion of SiH4 or other silicon compounds produces very fine particles approximately 0.5 µm diameter. This fine dust needs to be treated as the risk of exhaust clogging is too high to the production facility. Besides, small particles could affect the lung and the respiratory system of employees. The most common techniques to overcome the emission of particles are filters or electrostatic dust collectors Both technologies have the possibility to reduce fine particles emission but a standard filter has a high maintenance overhead due to the constant cleaning required. The collected powder is difficult to handle and often considered ‘special’ waste with the associated disposal costs. A maintenance free electrostatic dust collector is often the preferred choice by customers, where the particles are transferred into a water solution and treated by the waste water treatment facility in the fab.
The solar industry is very much used
to Turnkey-Solutions. For this reason it is common that customers look for a combined
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waste water and waste gas solution provider. DAS with it’s expertise in the PV industry allows the customer to take advantage of these synergies with opportunities such as cost saving through water recycling.
Wafer Based Technologies
The manufacturing of wafer based solar cells brings special abatement problems especially in the drying and firing of solder pastes used in the printing of bus bars and other similar patterns. In this process solvents are emitted from the solder paste and can cause numerous problems. These include the obvious health effects as well as problems in the fab exhaust system. The organic compounds condense in the piping, where they can leak out or even flow back to the process tool causing a possible fire or explosion hazard. This problem can be solved by an electrostatic condensate separator. The DAS solution JUNIPER, for example, chills the waste air rapidly. During this stage most of the organic compounds condense in the cooling stage. However, the waste air still contains some small particles and tiny aerosol droplets. During the second stage, the remaining compounds are removed through the use of a high-voltage electrostatic separator. The condensate is then collected in a tank, which can be automatically emptied in a safe way. The purified and cooled waste air can then be exhausted harmlessly into the environment.
Conclusion
While abatement tools will always be needed to secure a safe and efficient treatment of exhaust gases, clogging and emission of fine dust have became more critical points recently especially with the introduction of tougher government regulations. Thoughts regarding the usage of fuel gas or the handling of lye will keep abatement manufacturers collaborating closely with their customers in order to get the best production results. Tailor made solutions will dominate against standardized systems. Uptime and service therefore remain key competitive issues.
The tools will also become more and more energy efficient as smart signal interfaces to the process tool support actively the cost reduction regarding consumables and energy. And of course, public awareness as well as legal compliance will push the need for smart abatement also in countries where the German TA-Luft standard is not yet the benchmark for industrial waste gas treatment.
www.solar-pv-management.com Issue V 2011
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