Economic Considerations for SMIF Implementation in New and Existing Fabs
Enhanced profit from a small investment has been the compelling reason to use SMIF in existing and newly built semi- conductor facilities.
By Sudhir Jain
Like all businesses, the semiconductor industry must continuously come up with new ways to maintain profit levels, and in the semiconductor business, the two factors driving profitability are advanced technology (new products) and manufacturing costs. Today, a new generation of semiconductor product will replace the last one every 12 months or less. This is far shorter than the three to five year product cycles of the past, and the timeframe is expected to shorten even further with advances in research and development techniques. The cycle time is also shortened to develop newer generations of manufacturing tools. Yet, semiconductor manufacturers had depended on those three-to-five year product cycles to recoup their investment and generate profits. No company can afford to build new fabs for each new technology and expect to maintain profitability.
The bottom line is that, to maintain profitability, semiconductor manufacturers have to maximize use of facilities and equipment while consistently introducing new manufacturing technology. The keys to successfully generating profits are:
Maximize the utilization of facility and equipment once installed;
Maximize the product yield and operational efficiency while reducing operational cost;
Shorten the cycle to take new products from R&D to manufacturing or time to market;
Selectively replace the equipment with more efficient or superior equipment for higher throughput or complex processing as required;
Reduce down time in equipment or factory upgrades.
SMIF technology offers several cost-benefit factors to both new and existing fabs, however other issues must be considered.
Common Economic Considerations
Yield enhancement is the most publicized benefit of SMIF Technology. Current users report from 5 to 20 percent increases in yield as a direct result of using SMIF, and the majority of these yield enhancements are a direct result of the reduction in particulate contamination. The use of SMIF technology virtually eliminates contamination from storage and handling (wafers spend on average 80 percent of their factory life in storage or transport) and there`s an order of magnitude improvement in particulate levels on SMIF, equipped tools in Class 1000 cleanrooms compared to conventional Class 1 cleanrooms.
The expected yield enhancement from the use of SMIF can be calculated using yield loss information from an existing non-SMIF line, similar processes and established models. Users must use actual average yield data generated over a period of time. The airborne particle count or particle-per-wafer-per-pass tests can be misleading.
These test results invariably lead to the conclusion that the cleanroom has lower levels of contamination than that of actual work conditions. Cleanroom operations have a tendency to fall into more disciplined modes when particle probes or known test wafers enter the operation.
Air management systems make up a significant portion of a fab`s total operational electrical costs while the use of mini-environments can reduce these costs by up to 65 percent. The creation of a localized, clean isolated process environment allows more efficient use of air, thereby, reducing the total volume of air requiring purification and conditioning. Of course, individual cost savings are highly dependent on the cost of electricity in respective geographic areas and the factory will also need to be willing to reduce the overall cleanliness requirements in the area outside the mini-environments. Several studies have shown, however, that SMIF technology is highly effective for manufacturing submicron geometries in Class 1000 cleanrooms or less.
Exhaust requirements can be reduced significantly through the efficient use of mini-environments. Savings in scrubbing costs, reduced make-up air requirements and reduced operator exposure can represent significant savings in total operational costs.
Gowning costs can also be reduced by up to 75 percent in materials alone. Because SMIF technology completely isolates the wafer through the entire production cycle, the most direct impact is on the relaxation of gowning protocols. Instead of bunny suits, the operators can work in smocks, hair nets and shoe covers.
In addition to the direct $1-1.5 million savings in material cost, there are additional, but less quantifiable savings. The average loss in production time per shift per operator from gowning is about 90 minutes or 20 percent. Add to this the fatigue and discomfort due to the bunny suits, and an additional loss of efficiency in the range of 10 percent results. By eliminating the need of full bunny suits, a factory could theoretically reduce the number of operators required by up to 25 percent. Again, however, the factory must be willing to accept a reduction in gowning protocols.
Equipment density can also be increased in SMIF facilities because SMIF technology eliminates the need for separate service and production areas and optimization of tool layout. Although the actual increase in equipment density will depend upon specific circumstances such as current density, level of automation and building space, wafer throughput can be increased by up to 20 percent. There`s an increase in capital cost due to the increase in equipment, but the facility cost is not adversely affected.
Service efficiency benefits are very difficult to quantify. The elimination of separate service areas, however, not only reduces the time to access the equipment but also reduces the MTTR (mean time to repair) as a result of complete access to the equipment.
Misprocessing can virtually be eliminated by combining material tracking and control systems with SMIF technology. Factories using open-cassette processing have 5 percent or more on average in-line yield losses as a result of misprocessing. SMIF technology provides an I/O port on the machine as a safety interlock to prevent misprocessing. The process lots are stored in the SMIF Box and an intelligent system on the SMIF I/O port verifies the material ID prior to removing the product from the box for processing.
An automated material tracking and control system coupled with a proper mix of tool sets to ensure tool availability can reduce cycle times from 60 to 90 days to six days. The result is 70 to 80 percent reduction in the cost of work-in-progress alone while additional savings are realized in increased throughput.
Facility useful-life expectancy is one of the most important benefits of SMIF technology. Self-contained mini-environments (with built-in fan filter modules) can be replaced along with equipment. The selective replacement of process tools without affecting the rest of the operation can contribute significantly to the bottom line. Because the new process equipment comes with its own cleanroom, the fab is able to maintain an optimal mix of new and old tools to run an efficient manufacturing operation over a longer period. Process tools can be replaced to take advantage of enhanced processing capabilities, higher throughput or simply to replace an old machine with a new one.
Economic Considerations in Retrofit Fabs
Many fabs are in existence today with Class 10 to 10,000 operational cleanliness. Some are stretching the life of the facilities, equipment and environmental control systems. As the fabs continue to age, their production efficiencies continue to fall while their operational costs are shooting up. Yet, the high cost of a new fab and the loss of production could have devastating results for a company. Not only will it lose revenue during the ramp-up phase of the new facility, it will also run the risk of losing customers. Shutting down and upgrading the existing facility will have similar consequences. Several factors can help the fab manager decide the feasibility or optimal time of a SMIF implementation.
Reduction in defect densities through the use of SMIF will allow for migration to smaller geometries. Production costs can also be reduced as more products are produced on the same silicon with the same processing. Some equipment changes may be required to migrate to the smaller geometries, however, an immediate yield increase of 5 to 20 percent, depending on the current yield, can be realized. Current users report a payback in as little as six months.
Process qualification and yield learning time is also less than that of a conventional cleanroom, resulting in increased tool utilization and revenue generation during the useful life of the equipment.
The increased return on investment can be calculated by factoring in the increased level of production and revenue growth. Careful scheduling can minimize the SMIF implementation time on a tool to an average of eight hours.
Economic Considerations in New Fabs
The cost of a conventional Class 1 ballroom fab has increased considerably in the last few years. With the current price tag at about a $1 billion, and projected to double in the next four years, semiconductor manufacturers have been forced to look at alternate approaches.
Recent studies have concluded that the optimal fab of the future will utilize SMIF technology to reduce capital investment and generate higher rates of return.
In a new fab, a carefully selected and implemented strategy can add to cost savings and profitability as a result of the following factors:
The cost of materials used for walls, ceilings and floors can be reduced by up to 20 percent. The cost savings result from reduced cleanliness requirements, reduction in square footage, and a reduction in ceiling load requirements. The loading requirements are significantly reduced by the use of self-contained mini- environments.
SMIF and mini-environment costs are minimal relative to overall project costs, representing less than 3 percent of equipment costs. Also, process equipment is increasingly being made available with integrated mini-environment and SMIF ports. By the year 1998, more than 60 percent of process equipment is expected to be available with SMIF as a standard option. The cost of SMIF on these tools is about 65 percent less than the adapted solutions. Additional savings in the range of about $1 million will result from reduced overhead in procurement and project management costs. The cost of SMIF is highly dependent on the equipment type, but the average cost for existing fabs is in the range of $50,000 to $60,000 per tool. This estimate is based on a combination of integrated and adapted SMIF solutions. SMIF vendors can provide an accurate estimate of the cost of SMIF, once the equipment list is finalized.
Early yield learning can significantly shorten the time to wafer production. A recent study estimates that the combination of SMIF and other advances in manufacturing technology can result in 60 percent more shippable products in the first two years of fab operation. Since process tools are in commission as soon as the equipment is in place and utilities are hooked up, construction and installations can continue in adjacent areas. Wafer production in a SMIF fab typically begins up to four months earlier compared to a conventional fab.
Equipment layout in a SMIF-equipped fab will be more flexible for a new fab compared to an existing fab. The cost savings can be calculated from the reduced process cycle time and space requirements. Speed of material transport can also be significantly increased because the wafers are secured in SMIF boxes and can be transported at a higher speed. Facilities with inter- and/or intra-bay automated material handling systems can really take advantage of SMIF box transport because the speed of material transport in such cases is limited only by the speed of the automation system. The SMIF box also eliminates any contamination issues associated with the use of automated material handling systems.
The factors described in this article coupled with a financial analysis and an assessment of the unique factors affecting each individual situation can help a factory manager choose the optimal way of implementing SMIF. n
References
Castrucci, Paul; Griffin, Jim and Malcom Williams. “Design of Single Wafer Future Logic Fabs,” ASMC”94 Proceedings.
Weiss, Randy S. “SMIF Concept: Production Implementation of Micro-Environments,” Microcontamination `90 Proceedings.
Jain, Sudhir. “SMIF Isolation Technology in the 90`s,” ES `93 Proceedings.
Sudhir Jain is vice president of North American Operations at Jena-System GmbH. He has been engaged in the field of contamination control and automation technology for the last eight years. Prior to starting the North American Operation for Jena System in February 1994, he was involved in the R&D of SMIF-technology-based wafer manufacturing for four years. He has managed development programs for controlled environment (nitrogen ambient) SMIF technology along with developing air-flow management techniques.
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Jenoptik`s SMIF Lean Robot automatically transfers the wafer carrier from the SMIF box to the according equipment. The SMIF device was developed for use in Class 1 cleanrooms.