MODELING AND PERFORMANCE ANALYSIS OF CLUSTER TOOLS USING PETRI NETS

The performance of cluster tools is gaining ever-increasing importance as the semiconductor industry migrates to larger wafer sizes, and sma ller device geometries. Customers demand higher throughput-to-footprin t ratios for semiconductor equipment. Cluster tool throughput is the o utcome of complex interactions of various subsystems, and there is a c ritical need for appropriate tools that aid in understanding these int eractions, and their effects on throughput. Current methods for throug hput analysis are not very well oriented toward understanding the dyna mics in cluster tool processing. In this paper we present a procedure to model cluster tools using Petri nets. These models help designers t o comprehend the Bow of wafers during processing. While Petri nets hav e been used extensively in the modeling and analysis of diverse manufa cturing processes/systems, this to the best of our knowledge is the fi rst attempt to specifically model cluster tools. A state cycle analysi s is discussed next; this method enables equipment designers to extrac t steady state throughput information, as well as understand the inter play of subsystems during the wafer flow. Two example configurations a re used to illustrate Petri net-based model building and analysis. The se two examples encompass a variety of design features found in the in dustry today, e,g,, sequential and parallel processing, single and dua l end effector robots, anticipatory and simple scheduling.