Saving with automated control of maintenance/parts logistics
08/01/2002
By Carl N.R. Dellar, Dalia Vernikovsky, William Cockerill, Eshinui Inc., Hayward, California
 A maintenance technician checks via a PDA on the availability of spare parts from within the cleanroom at NEC Electronics in Roseville, CA. |
Overview
In semiconductor wafer fabrication, as much as 10% of wafer production costs are associated with spare parts. Automated control of parts and associated logistics can help manage this manufacturing cost component and provide better maintenance technician productivity. Early tests of such software capability at NEC Electronics have given fab operations improved management of its relatively costly vacuum-pump refurbishment cycle.
The semiconductor industry has increasingly turned to software tools to improve productivity and return on investment. MES, SECS-GEM data collection, and analysis tools have become standard in fabs. Outside the fab, MRP-ERP software has become the norm. Software for maintenance and spare parts logistics (MSPL), however, is still in its infancy. Yet the need for MSPL is crucial.
Price tags for individual pieces of capital equipment range from $1 million-$10 million. Downtime can exceed $300,000/hr. In leading-edge fabs, annual expenditures for consumables and spare parts run $30 million-$150 million and can account for up to 10% of wafer production costs.
At any given point, the value of a fab's spare parts inventory can total $30 million-$60 million. Many of these parts can sit for two years or longer or never be used. Inevitably, a needed part not stocked at a fab is not stocked locally by the supplier either. Even if parts are available globally, a "stock-out" can create downtimes of a day or more depending on a supplier's logistics. Even when a part is at a fab, access to information is often slow. Fab managers report that 60% of an equipment technician's time can be spent looking for parts and information.
 An overview of MSPL software cast within the framework of a semiconductor manufacturing fab. |
Workable MSPL software
Clearly, this industry needs software that is capable of giving immediate feedback on availability and utilization of equipment parts and associated analytical data. We have focused on these needs in developing the Rover software package.
Such capability must integrate with existing MES, SECS-GEM, and MRP-ERP software because standalone applications are simply passé. Portability and easy portal access is also important, including compatibility with PCs or, ideally, wireless PDAs or tablets. The latter gives maintenance personnel and engineers immediate access to tool and spares histories and inventory locations while they are in the cleanroom or the sub-fab. If it is to be properly used and functional, MSPL software needs a platform that is common, simple, and scalable and resides on a server that is accessible by a common industry browser. MSPL also requires a comprehensive set of modules that address cross-functional needs, including equipment engineering and maintenance, and supplies (see illustration).
Nine foremost areas
We have identified nine key areas (see following) that any MSPL solution should provide.
1. Equipment service management. This area should include interactive HTML preventive maintenance (PM) procedures and reference documentation; self-auditing digital signoff that ensures complete and correct documents; time tracking of multiple procedures and technicians; justification of manpower based on workloads; identifying training needs; highlighting the need to optimize PM time vs. production time; customizable Pareto classification; and posting of "flags" related to future scheduled maintenance events.
2. Spare parts and tool warranty management and tracking. In today's fabs, individual spare parts and tool warranties have become complex because various peripherals and subassemblies can come with warranties separate from the tool warranty. Losses associated with unclaimed parts warranties can add up quickly. A part's warranty status needs to be tracked in inventory or on a tool, and parts need to be pulled when repairs or services are needed so that warranties do not expire. This capability requires barcode support even with a wireless PDA.
3. Refurbishment management and tracking. Fabs often have a large dollar volume of parts in a refurbish or cleaning loop. Often, this can trigger unnecessary use of a new part. These situations are better controlled when individual-part histories are tracked through a tool, multiple tools, and repeated refurbishment. Such tracking should also provide guidance about part retirement after multiple refurbishment cycles, factor in multiple end-of-life criteria (i.e., RF hours, part thickness, etc.), and provide electronic access to the refurbishment vendor so that test data and certificates of conformance can be accessed. It is also helpful if the software automatically generates overdue reports with progressive (i.e., 30-, 60-, 90-day) escalation and sends e-mail alerts up the management chain of command.
4. Kitting management and tracking. Increased use of PM kits adds a new level of complexity. With copper processing, for example, kit components must be clearly identified and kept separate from all other kits — which could contain some of the same parts — all the way through the kit-refurbishment loop and into the stockroom. In addition, the software has to "see" inside pre-built kits to find parts that can solve tool-down situations, following up with kit rebuild instructions.
5. Calibration management and tracking. Calibration schedules and forecasts must become a key part of a fully automated solution. Calibration is often the first item checked when a process goes out of specification, but this is typically managed at the tool-owner level with disparate manual methodologies, rather than at the fab level. Automated management also aids in electronic certification documentation for ISO9000 audit compliance.
6. PM scheduling and parts forecasting. Preventive maintenance is one of the largest uses of equipment maintenance manpower, so scheduling and forecasting parts requirements is critical to using that time efficiently and returning tools to production quickly. Here, a key is to ensure that parts are available ahead of a PM and to use PMs to forecast parts requirements. The goal should be close to just-in-time availability, thereby increasing inventory turns, minimizing time in inventory, reducing risk of damage in inventory, and reducing inventory costs. Weekly PM schedule reports are essential along with integrating parts availability into MRP-ERP software for procurement coordination.
7. Spare parts and tool performance management. The most effective way to correlate spare parts quality and maintenance activity to tool performance is to correlate yield and process performance to spare parts activity and maintenance activity in a tool. This can be done by integrating to the SECS-GEM database and matching timelines. Then, multiple source spare parts can be evaluated to select the best sources and to identify bad lots. It is also important to compare tool performance to identify low performing tools. Spare parts performance information is also critical to optimizing PM schedules.
8. Spare parts and consumables management. Tracking spare parts all the way to the tool, maintaining a history of spares on each tool, and maintaining a history of where each spare part has been in its life is essential to overall equipment effectiveness (OEE). Spare parts activity reports need to be generated per tool, per toolset, and per fab. These reports can be used as an analysis tool to reduce spare parts utilization and drive both internal and external continuous improvement programs. Combined with wireless PDA access, such capability can be an important productivity driver for maintenance technicians.
9. Wafer probe card management and tracking. Wafer probe card collections tend to be extremely large — particularly in silicon foundries — and often multiples of each card are required. Wafer probe cards have their own unique refurbishment loop. Since each probe card is tied to a specific product or product family, its expeditious availability is critical. Full visibility of all cards and their status, whether in test, inventory, or out for refurbishment is critical. Good automated control here would allow, at the fab's discretion, card refurbishment suppliers to have password access that provides status updates on probe cards in the refurbishment loop. Upon return, the vendor can also provide electronic copies of certificates of conformance.
 An NEC technician with a PDA uses the Rover system to access information on tool status. |
Automatic report generation and distribution are especially critical because of a probe card's direct ties to product. Integration to MES is significant because it provides information about specific production wafers that are on the way, thus predicting probing needs. Product wafer start information from MES can be used to identify when additional copies of a specific card are needed. This should be issued from automatic report generation, to include e-mail and pager alerts and to generate and distribute vendor overdue reports. Integration is also critical to manage and optimize touch counts to determine when a card needs refurbishment.
MSPL in action
In early tests, engineers at the NEC Electronics manufacturing plant in Roseville, CA, used our refurbishment management and tracking module for 3½ months, specifically on vacuum pumps throughout their fab. At NEC, a supervisor had been tabulating information weekly about pump pressure and temperature, and managing refurbishment cycles to subcontractors, a time-consuming process. But with MSPL software, the supervisor was better able to "get his arms around something that is a significant asset and a significant piece of inventory."
The MSPL software module provided NEC Electronics with a central location for data capture and visibility, tracking, and reporting about its pumps. The fab's turbo pumps, costing tens of thousands of dollars, lacked complete histories, clear information about the refurbishment process, and immediate information about pump problems (e.g., premature failure, etc.).
 An NEC technician with a PDA uses Rover to capture system data. |
This application of MSPL at NEC Electronics provided the statistical analysis that proved the system's value through dynamically generated reports on parts, prices, length of life, etc. The fab is now using this module to control ion implantation parts and a much larger scale of utilization by using the kitting software module. Recent adoption of this software has given engineers a tool to manage costs in an area where previously no tools existed.
Acknowledgments
We thank Frankie McDermott, director of equipment engineering, and Dave Long, equipment supervisor, at NEC Electronics Inc. Rover is a trademark of Eshinui Inc.
Carl N.R. Dellar received his BSc in computer science from the University of Manchester and his PhD in computer science from the University of Cambridge. He is president and VP of engineering at Eshinui Inc.
Dalia Vernikovsky is VP of business development at Eshinui Inc., 24301 Southland Dr., Suite 207, Hayward, CA 94545; ph 510/264-3435, fax 510/264-3445, e-mail [email protected].
William Cockerill received his BA in mechanical engineering from the University of Illinois at Urbana-Champaign. He is director of NA sales at Eshinui Inc.