interview industry
operates with clearances set to account for the thermal properties of the gas, and integrates a progressive nitrogen purge capacity to offset the challenges of pumping this lighter gas at higher pressures. Finally, since hydrogen is flammable if mixed with an oxidant such as air, the pump exhaust must be appropriately managed to avoid ignition.
Figure 2: Edwards’ iXH dry vacuum pump has been specifically designed to handle the high volumes of ammonia and hydrogen involved in HBLED production
pumping at low pressures, they become a problem when the gas is compressed towards atmospheric pressure in a vacuum pump. At these pressures, due to its low viscosity, hydrogen tends to leak back through pump clearances, reducing the effective pumping speed. Hydrogen also has a much higher thermal conductivity (seven times greater) than heavier gases such as nitrogen. As a result, systems pumping hydrogen typically have a different thermal profile and different component dimensions than those pumping nitrogen. A pump optimized to deal with hydrogen ideally
No. tools per abatement system Fresh water cost Waste water cost Power cost
Nat. gas cost H2 cost
CDA cost H2SO4 dosing cost NH3-N treatment by Gas striping tower
Value of Ammonium sulphate recovered from gas stripping Heat recovery N2 Cost
GaNcat cartridges/year GaNcat Cartridges disposal costs/year
Potential value of heat recovered from exhaust gas
Total Utility Cost
As mentioned earlier, pumps used in the metalorganic chemical vapor- phase deposition (MOCVD) processes used to manufacture LEDs also handle high volumes of ammonia. This means they must be highly corrosive-resistant. Modular dry pumps have proven to address the challenges of pumping both ammonia and hydrogen in a production environment, while also offering potential CoO savings. Edward’s iXH pump (Fig. 2), for example, has been specifically designed to meet the challenges associated with pumping high volumes of ammonia and hydrogen with enhanced purge flow, temperature-controlled operating range, light gas performance and corrosive resistance and improved
Abatement System SG3000
6
$0 $0
$4,505 $2,147 $501 $0 $0 $0
$0
-$20,000 $158 $0 $0
$0
-$12,689 $4,702
Figure 3: Cost Comparison of Operating Costs for Combustion-Based Systems vs. Wet Scrub Abatement Systems
Wet
3
$4,505 $0
$751 $0 $0 $0
$1,430 $751
-$2,893 $0
$158 $0 $0
powder handling. In addition, Edwards’ pumps incorporate a unique, proprietary seal technology that helps to prevent ammonia leaks. These capabilities reduce maintenance intervals and extend pump life, thereby helping to reduce overall tool CoO. The vacuum pump offers further CoO savings through reduced energy consumption.
Exhaust Gas Abatement
In LED manufacturing, the extraction, safe handling and disposal of gases from MOCVD processes significantly contribute to manufacturing CoO. The conventional approach to exhaust gas management uses a wet scrubbing technology that adds significant costs to the manufacturing process in terms of energy use, water consumption and treatment.
Combustion-based abatement offers an attractive alternative to wet scrubbing. While capital costs are approximately the same, combustion- based abatement systems offer greatly reduced operating costs, as illustrated in Figure 3. Their large input flow capability, typically equivalent to three to five process tool exhausts, eliminates capacity constraints and helps minimize capital expenditures. At the same time, their use of the exhaust gases as the main fuel in the abatement process significantly reduces energy costs. In addition, innovative reaction chemistries minimize the formation of unwanted by-products such as nitrogen oxides (NOx), a regulated emission, or ammonium solids, which require increased system maintenance downtime, thereby reducing tool productivity.
The wet scrubbing technology typically used in the GaN MOCVD process essentially bubbles the gases through a tub of water where they are absorbed. This process, however, does not remove hydrogen, which is the most common waste gas produced in the MOCVD process. While hydrogen emissions are not regulated, allowing the gas to be vented directly into the
April/May 2010
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