Film interface control in integrated processing systems*

Abstract

A number of system concepts in which the integrity of substrate surface and film interfaces are preserved are discussed. This includes stand-alone tools with internal clean air or nitrogen facilities with wafer transfer between such tools in clean containers (‘‘minienvironments’’) and single-wafer and batch-type cluster systems in which the processing and wafer transfer modules are physically connected. Depending on the cleanliness requirements, wafer transfer and processing are done in pure atmospheric nitrogen, low-pressure nitrogen, or vacuum. An analysis is given in which the ambient requirements are related to surface reactivity, wafer transfer time, and acceptable surface contamination level. Trade-offs in terms of capital cost, throughput, flexibility, and film quality are analyzed. A number of different system concepts combining wafer preclean, thin oxide growth, and poly-Si deposition processes are analyzed in terms of their economical performance. It appears that single-wafer systems have a logistic advantage in terms of short cycle time and wafer inventory; however, the cost per wafer of batch-type systems is considerably lower than single-wafer ones. It is shown that the optimum choice between (fast, high-temperature) single-wafer and (slow, low-temperature) batch-type systems in terms of process performance depends on physical parameters such as activation energy and the occurrence of undesired, competing, processes.