A logistical management system using calculated raw-process-time factors for production control

In 1990, the IBM semiconductor manufacturing facility in Essex Junction, Vermont, fabricated two basic types of memory products in one of its fabricators with a "first-in first-out" (FIFO) system for tracking individual wafer lots. When additional products in different technologies came on line, a "pull range system" was used to divide wafer processing into 24-hour segments. These ranges consisted of one to ten operations that were scheduled for completion in one day. By early 1993, the number of different products being produced at this semiconductor manufacturing facility increased significantly, exceeding the ability of production operators to view and manage these pull ranges. This paper describes a logistical management system that uses a calculated raw-process-time factor to control product. The system, installed on the wafer processing line, focuses on a stock date and raw processing data to organize and prioritize all product lots into one system. The stock data describes when a particular product lot is due, while the raw processing time defines the amount of time required to process a lot from beginning to end. This system has helped to maintain fabricator serviceability ratings in the high 90% range and is available to all operators, especially those processing lots that require the most attention (those behind schedule). Data derived from the system describes wafer-lot priorities and the order in which the lots must be run. The system prioritizes all lots being processed for each operation, thereby enabling operators to simply "run the top lot".