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WAFER FAB CYCLE TIME MANAGEMENT USING MES DATA

WAFER FAB CYCLE TIME MANAGEMENT USING MES DATA - WAFER FAB...

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© 2000 by Simulation Councils, Inc. Reprinted, with permission, from Proceedings of the MASM 2000 Conference, Tempe, AZ, May 10-12, 2000. 1 WAFER FAB CYCLE TIME MANAGEMENT USING MES DATA Jennifer Robinson and Frank Chance FabTime Inc. 325M Sharon Park Drive #219 Menlo Park, CA 94025 www.FabTime.com KEYWORDS: Cycle Time Management, Manufacturing Execution System (MES) ABSTRACT: A critical factor for most wafer fab managers is maintaining acceptable cycle times. In the highly variable environment of a wafer fab, this is no small task. Batch processing, tool dedication, unreliable equipment, setups, rework, and hot lots all conspire to drive cycle times upward. To combat these factors, we propose a methodology for cycle time management based on extracting real-time data from the manufacturing execution system (MES). We use the MES data to identify problems on the shop floor, and then draw on our experience in cycle time management to recommend improvement strategies. We first review the cycle time management information that can be derived from lot move data alone. Next, we highlight other improvement areas for which additional MES data must be collected. Finally, we indicate the point at which users must turn to simulation to perform further what-if analysis. INTRODUCTION A critical factor for wafer fab managers is maintaining acceptable cycle times. Long cycle times are associated with high inventory cost, poor line yield, and lost opportunity. Sales are sometimes lost by those fabs that cannot offer the lowest cycle times. Planning for acceptable cycle times costs money, too. Fabs are generally run at only 85% to 90% of their maximum capacity, leaving a 10-15% cushion to guard against the high cycle time caused by variability. By reducing this variability, a factory can often increase the actual throughput rate at which it operates, yet achieve the same average cycle time. Increasing throughput with the same equipment set (if the additional products can be sold) translates into a direct improvement of the bottom line. In the highly variable environment of a wafer fab, reducing cycle times is no small task. Many factors conspire to drive cycle times upward, including batch processing, tool dedication, unreliable equipment, setups, rework, and hot lots. While many of these factors cannot be eliminated, their cumulative effect can often be improved. This paper presents a systematic process for improving fab cycle times through the use of data extracted from the factory manufacturing execution system (MES). METHODOLOGY The first step towards reducing cycle times without purchasing capital equipment is educating personnel to understand the effects of variability. The next step is identifying problem areas in the fab by looking at actual MES data. This data should be made prominently available for employee review and motivation. Next, operating practices must be modified, and the impact of the changes on cycle times verified. In some cases, simulation must be used for longer-term analysis.
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