Proceedings of the 2000 Winter Simulation Conference J. A. Joines, R. R. Barton, K. Kang, and P. A. Fishwick, eds. SCHEDULING MEMS MANUFACTURING Wang Lixin Francis Tay Eng Hock Department of Mechanical and Production Engineering National University of Singapore 10 Kent Ridge Crescent, SINGAPORE 119260 Lee Loo Hay Department of Industrial and Systems Engineering National University of Singapore 10 Kent Ridge Crescent, SINGAPORE 119260 ABSTRACT This paper focuses on the production scheduling in MEMS (Micro-Electro Mechanical System) manufacturing. The whole MEMS production process can be organized into 3 sub-processes, i.e., the wafer front-end process, the wafer cap process and the back-end process. Every wafer processed by the wafer front-end process needs to be bonded with a wafer that is manufactured in the wafer cap process, and then it will be sent to the back-end process. Therefore how to synchronize the release of wafers into the front-end process as well as the wafer cap process becomes an important topic. An ineffective coordination will create long cycle time and large WIP (work-in-process). In this paper, four synchronization rules are developed and they are evaluated together with two release rules and five dispatching rules. The performance measures considered are cycle time, throughput rate and WIP. A visual interactive simulation model is constructed to imitate the production line. The simulation results indicate that synchronization rules, release rules, and dispatching rules, have significant impacts on the performance of MEMS manufacturing and the best policy combination is Littlesyn-CONWIP-SRPT. 1 INTRODUCTION MEMS (Micro-Electro Mechanical System) is integrated micro devices or systems combining electrical and mechanical components fabricated using integrated circuit (IC) compatible batch-processing techniques and range in size from micrometers to millimetres. These systems can sense, control, and actuate on the micro scale and function individually or in arrays to generate effects on the macro scale. MEMS can be used to provide robust and inex- pensive miniaturization and integration of simple elements into more complex systems. Current MEMS applications include accelerometers, pressure, chemical, and flow sensors, micro-optics, optical scanners, and fluid pumps. Since MEMS is the integration of mechanical sub- strate through the utilization of microfabrication technolo- gy, its processes combine IC processes with highly- specialized micromachining processes. The electronics components are fabricated using integrated circuit (IC) process sequences, while the micromechanical components are fabricated using compatible micromachining processes that selectively etch away parts of the silicon wafer or add new structural layers to form the mechanical and electromechanical devices. Therefore, the process flows and the equipment used in MEMS manufacturing are very similar to those for wafer fabrication, which is one of the worlds most complicated manufacturing processes. The production flow of a wafer may re-enter the similar sequence of machine groups from layer to layer in its fabrication process. Owing to the re-entrance nature, wafers of different types as well as different layers of fabrication may compete for resource. Besides, there exist huge uncertainties in operation due to frequent machine failure and fluctuation of yield rate. Therefore, it is very challenging to develop sound scheduling rule in wafer fabrication. The same scenario will be expected in MEMS systems. However, the MEMS production is not the same as wafer fabrication and has its own characteristics. The MEMS manufacturing studied in this paper is based on a commercial SCREAM (single crystal reactive etching and metallization) micro-machining technology. This tech- nology uses reactive ion etching both to define and release structures (Mardou 1997). SCREAM portrays a relatively new micromaching approach and represents an important new technique from several points of view. It is a self- aligned, single mask process, run at low-temperatures (<300 0 C), and completed in less than 8 hours that can be carried out in the presence of integrated circuitry on the same chip. This production process can be broken into 3 sub-processes, the wafer front-end process, the wafer cap process and the back-end process (see Figure 1). Raw wafers are processed in batches of 18 in the front-end process and the wafer cap process concurrently. One output 1472