industry interview
atmosphere, there is a slight, but potential danger that static electricity could ignite the hydrogen during the abatement process, causing an explosion and fire.
The second most common gas produced as a by-product of the MOCVD process is ammonia. While water scrubbing can eliminate this gas, there is a danger, when hard water (water containing calcium or magnesium salts) is used, that the ammonia will react with the salts in the water producing ammonium solids. Hard water occurs anywhere that mountain run-off is a major source of water, which constitutes a large portion of the globe. As mentioned earlier, these ammonia solids can build up in the system, thereby increasing maintenance requirements and increasing CoO.
Combustion-based abatement technology solves both these problems by burning the exhaust gases in a controlled way. (Figure 4 provides a schematic of a typical four-stage combustion abatement system.) The only outside energy required is that to operate a small pilot light, similar to the ones used in home gas furnaces or stoves. Not only does this approach eliminate the hydrogen safety issue and the maintenance problem caused by ammonium solids, it offers significant reductions in energy costs compared to wet scrub technology.
In addition, the combustion-based system is air cooled, with the air flow being generated by the house extraction system. This air-cooled design ensures that combustion by- products are efficiently transported from the system to the factory central scrubber or dust filter. An air-cooled system eliminates many of the fixed and operating costs associated with a wet process, including the cost of the water itself, the capital and operating costs associated with water pumps, the energy to run them and water treatment costs. Air-cooled systems are also simpler in design and have fewer moving parts. As a
result, maintenance intervals are increased, while maintenance times and spares inventory requirements are reduced, all of which helps to further reduce system CoO.
When burning ammonia in a combustion-based abatement system, there is always the danger of creating NOx emissions, which are strictly regulated in most regions of the world. Edwards’ Atlas and Spectra G (Fig. 5) abatement systems avoid this danger by using a proprietary process that carefully controls the oxidation of the gases being burned to minimize NOx emissions.
In addition to the benefits of combustion-based exhaust systems in terms of safety, lower CoO and reduced environmental concerns, combustion-based abatement technology has a well-established track record for reliability. Hundreds of combustion-based exhaust abatement systems are deployed at a variety of companies in the semiconductor, flat panel and solar cell industries. The efficiency of its gas treatment process has been field-tested and meets the most stringent air emission regulations in Europe, the United States and Asia. It is currently experiencing a high rate of adoption by leading LED manufacturers world wide.
An Integrated Solution
The benefits of integrating related subsystems in a manufacturing tool has been proven in a variety of industries, such as semiconductor and flat panel manufacturing, to help reduce overall manufacturing CoO in a variety of ways. For example the combined vacuum and exhaust management systems provide enhanced safety, process tool compatibility, minimum footprint and reduced CoO. In addition, since they are housed in a single extracted cabinet with a single utility connection, these integrated systems provide a highly cost-effective means of providing protection should leakage occur.
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www.compoundsemiconductor.net April/May 2010
Using an integrated vacuum pump and abatement system, such as Edwards’ Zenith system can reduce installation time by up to 70 percent, cut installation costs by over 60 percent and eliminate over 50 percent of facilities connections. Overall capital expenditures are also significantly reduced. In the case of phosphide MOCVD, the Zenith also significantly improves the safety when dealing with toxic gases like phosphine and arsine.
Author Biography: M.R. Czerniak, Product Marketing Manager, Exhaust Gas Management, Edwards.
Mike Czerniak received his PhD at Manchester U., and started as a scientist at Philips’ UK laboratories before moving to its fab in Nijmegen, working on compound semiconductor applications. He was in marketing at Cambridge Instruments and VG Semicon; he is now the product marketing manager of the Exhaust Gas Management Division of Edwards.
Figure 4: Four Stage Combustion
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