A cluster tool consists of several single-wafer processing modules (PMs) and a transfer module (TM) based on a wafer-handling robot. This paper presents a systematic object-oriented architecture for designing and implementing cluster tool control applications. This architecture incorporates management functions for process, log, alarm, file, and I/O which are critical in cluster tool control applications but have not been discussed in other papers. This paper also discusses implementation issues as well as the real control application which has been implemented and tested on a real cluster tool.