Ammonia for Blue LED Production, from Supply to Abatement
Van Gompel, Joe; McPoland, Natalie; Lemouze, Robert; Czerniak, Mike
(All authors with BOC Edwards. (Van Gompel, Austin TX) (McPoland & Lemouze, 575 Mountain Ave, Murray Hill, NJ 07974) (Czerniak, Kenn Road, Clevedon, N. Somerset, England, BS21 6TH))
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LoginBlue LED production (based on gallium nitride) requires high flows of ultrapure ammonia (up to 100 slm per reactor). Bulk supply of very high purity (99.99998%) NH3 can be done through shipment of bulk crude NH3 followed by cost-effective on-site purification. Bulk delivery is inherently safer than cylinder changeouts as the number of connects and disconnects is greatly reduced. After the LED process chamber, residual ammonia must be abated. Large flows of NH3 (and H2) contribute to extreme flammability, toxicity, odors, and pluming if not properly treated. Several abatement technologies are available for GaN epitaxy, depending on customer requirements. For example, since NH3 is very water-soluble at low pH, one solution involves a dosed water scrubber with sulfuric acid to remove NH3 from the exhaust waste stream to > 99.8%. Solution 2 involves a combustor/wet scrubber combination. The Helios is designed to burn up to 100 slm NH3 AND 100 slm H2 simultaneously. The inward-fired Helios combustor converts the NH3 to N2 and H2O with low NOx generation. Solution 3 involves catalytic decomposition of NH3 to N2 and H2 in a hot-bed dry reactor based on the reverse Haber process. This is perhaps the most cost-effective and clean exhaust management option for GaN epitaxy. To maximize both safety and cost of ownership / installation efficiency, the combination of the vacuum pumps and the abatement into a single cabinet has been successfully implemented on MOCVD processes. The Zenith system can be used with appropriate vacuum pumps and any of the treatment solutions (wet scrubber, combustor / scrubber, or dry bed scrubber) described above.