Managing WIP and cycle time with the help of Loop Control

As an adaptation of the CONWIP concept, AMD has developed a heuristic approach to control the WIP in its wafer fabrication facilities (fabs). The so called ¿loop control¿ concept helps to utilize the installed equipment in an efficient way and reduces the overall cycle time. Two dynamic constraints (the WIP-Limit and the THP-Limit) are defined to limit the WIP (work in progress) per photo layer and to tackle high WIP situations at individual operations inside a photo layer. Loop control has been evaluated with help of a fab simulation study prior to implementation in the fab dispatching system. Since its development three years ago, this system operates successfully in the AMD Dresden fabs.