Integrated UHP Gas Subsystems
Savings in capital cost and COO for ultrahigh-purity gas distribution systems can be realized through creative applications of integrated subsystems.
Larry Rabellino, Dave D'Agosta, SAES Pure Gas Inc., San Luis Obispo, Calif. Lorne Shille, Obayashi Corp., Tokyo, Japan James Herron, Lockwood Greene, Spartanburg, S.C -- Semiconductor International, 3/1/1998
Ultrahigh-purity (UHP) gas distribution systems consist of a variety of components, including various types of valving, purifiers, filters, sensors and devices that control pressure and flow. While it is common to integrate components in gas boxes at the process tool, bulk gas components are typically installed on-site as part of the overall system installation.
As illustrated in the following example, it is possible to significantly raise the level of integration in gas distribution subsystems -- which can be assembled off-site and installed as a single "component" outside the fab. This helps lower overall system capital cost and cost-of-ownership (COO) and can shorten leadtimes from contract award to certification. Integrated UHP subassemblies can include, as a minimum, the following components: pressure relief, pressure control, flow control, isolation valving, bypass valving, check valving, gas purification, particle filtration, mass flow measurement, temperature measurement, pressure measurement, gas purity measurement, particle measurement, complete system data acquisition, closed loop cooling and compressed air source.
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Case study: Matsushita fab expansion
Obayashi Corp. of America (OC America) utilized an integrated subsystem approach in the expansion of the Matsushita (MASCA) facility in Puallyup, Wash. Together with Lockwood Greene, OC America installed nitrogen, argon and oxygen gas systems in dedicated outdoor enclosures, complete with gas purifiers, filters, bypass/isolation valving with parallel piping assemblies, pressure measurement, mass flow measurement, gas analyzers, sample lines and complete system data acquisition.
Space inside the fab was at a premium, and the existing facility constraints posed an interesting challenge to Obayashi. The optimum location to place these gas system components from the gas delivery perspective was not ideal from an architectural view. Most importantly, the extremely aggressive cost-containment goals required creative solutions to make the most of the expensive fab floor space.
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Industry leaders allow up to $4500 per square foot of floor space within the fab. MASCA's target was less than half that, at $2000 per square foot, not including distribution piping and engineering costs. The gas distribution piping, used to link components and subassemblies, ranges from an additional $300 to $500 per square foot in the appropriate location, i.e., the gas purifier/analyzer room. This yields $2500 per square foot of capital cost (less engineering), which Lockwood Greene used as a basis for cost studies. Using the integrated UHP subsystem concept, the capital cost for the installation was more than 15 times less than the same system inside the fab.
The task at hand was to limit and optimize the floor space inside the fab by relocating appropriate components or systems. This need initiated the concept of integrating many gas distribution components into dedicated NEMA 4 enclosures, located outside the fab. Clearly, the gas delivery system equipment is low maintenance, requiring minimal personnel accommodations. There is no benefit to using costly building space designed for personnel traffic when only service access is needed. In addition, more efficient equipment arrangement inherent in a single integrated design will reduce the total square footage of area required to accommodate the gas distribution components. Lockwood Greene recognized the many benefits to this approach before breaking ground.
Project design efforts were reduced by the substitution of one component for that of up to 18 different component groups. Not just the gas system design efforts were reduced, however. Using the NEMA 4 outside enclosure further reduced architectural design concerns. For example, as these enclosures are considered small equipment storage units, building permits are not required (except for the foundation).
In addition to immediate savings in the design efforts, the entire MASCA team benefited from the reduced project management and procurement efforts. Project management is always simplified if the number of tasks is reduced. The same can be said of procurement. Risk was also reduced with fewer suppliers.
On-site assembly and certification cost reduction added to the savings. Assembly and fabrication (cutting, facing, welding) is always more costly and problematic on-site rather than off-site. Also, the nature of the single, compact enclosure subsystem provides better dimensional control over in situ assembly. Interfaces and datums were more easily maintained in the smaller, well-controlled environment.
| Table 1. Space Cost Comparison of Gas Distribution Systems | |||||
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| (Integrated subsystem concept vs. in-fab purifier rooms) | |||||
| Description | Installation type | Cost ($/ft2) | Area (ft2) | Unit cost | Total cost |
| Integrated subsystem | Nitrogen/argon gases Oxygen gas | $300 | 120 | $36,000 | $64,800 |
| $300 | 96 | $28,800 | |||
| In-fab purifier room | Nitrogen/argon gases Oxygen gas | $2500 | 238 | $595,000 | $995,000 |
| $2500 | 160 | $400,000 | |||
Significant duplication of effort was also reduced by consolidation of multiple components into a single assembly. At each level of assembly, pressure testing and leak testing are often appropriate. In many circumstances, component and subassembly testing can include particle and impurity testing. Reducing the number of tiered subassemblies reduced the "redundant" tests performed on a given component. For example, the filters are qualified by the manufacturer for particle count and moisture. The filters are then welded to the next assembly (gas purifier or filter skid) and retested (the valves, tubing and fittings have of course also been component tested). Finally, the purifier or skid is installed on site and tested at least one more time.
In this simple example, at least one pressure/leak/quality test sequence would be eliminated, reducing system costs. Many of the tests negated by the integrated system concept are on-site testing, typically the most costly to perform.
Nitrogen, argon and oxygen units
The systems considered for dedicated, NEMA 4 outside enclosures were nitrogen, argon and oxygen. The nitrogen purifier (1500 M3/hr ) and redundant argon purifiers (50 M3/hr) were installed in a single outdoor enclosure. In addition, on-line oxygen detection analysis was included for the nitrogen gas, along with the data acquisition. Isolation valving, bypass valving, mass flow measurement, pressure measurement and particle filtration were provided inside the thermally conditioned modular enclosure.
In a separate location and enclsoure, redundant oxygen purifiers (30 M 3/hr) capacity, were mated to an on-line moisture analyzer. The system included particle filtration, bypass valving and mass flow measurement. The oxygen equipment was networked via TCP/IP, allowing a single reference point for all purification equipment data acquisition.
The nitrogen/argon unit (Fig. 1) required 120 ft2 (10 ft x 12 ft) when installed in the NEMA 4 enclosure. Because of the space efficiency of the integrated subsystem design, almost 50% of the 238 ft 2 needed for inside fab installation was eliminated.
The oxygen unit (Fig. 2) required 96 ft2 (8 ft x 12 ft) when installed in the NEMA 4 enclosure. Again, space efficiency of the integrated subsystem design reduced the 160 ft2 needed by 40%. Tables 1 and 2 provide cost comparisons, with actual costs for the integrated subsystem installations.
Capital cost was not the only benefit of the MASCA installation. COO was also dramatically decreased, as HVAC and lighting costs are optimized for both the reduced floor space and the reduced personnel occupancy time. Energy costs at 7.5 cents/kWh are typically estimated at $50 per square foot per year. Estimated COO comparison is shown in Table 2.
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Table 2. Cost-of-Ownership Comparison of Gas Distribution Systems |
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(Integrated subsystem concept
vs. in-fab-purifier room |
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| Description | Installation type($/ft2/year) | Cost (ft2) | Area | Unit cost | Total est. cost |
| Integrated subsystem | Nitrogen/argon gases Oxygen gas | $3.50 | 120 | $423 | $879 |
| $4.25 | 96 | $456 | |||
| In-fab purifier room | Nitrogen/argon gases Oxygen gas | $50 | 238 | $11,900 | $19,000 |
| $50 | 160 | $8000 | |||
Summary
Savings in capital cost and COO of UHP gas distribution systems for new construction or expansions can be realized through creative applications of UHP integrated subsystems. Building space can be optimized for the actual utilization requirements, whether equipment or personnel. Project management can be simplified through reduction in tasks.
