Cluster tool wafer handler reliability modeling using top-down and bottom-up methodologies

Brooks Automation produces automated, vacuum substrate-material-handling products for the semiconductor equipment industry. The Brooks Cluster Tool Wafer Handler is the Cluster Tool manufacturer's Central Wafer Handler (CWH) for PVD, CVD, RTP, etch, and other applications used to manufacture semiconductor devices. Since the Brooks CWH is integrated directly into the customer's Cluster Tool, the CWH reliability requirements are dictated by the Cluster Tool reliability requirements. Typically there is not enough time in the design and development phase to empirically determine the actual system reliability (with confidence). Therefore, reliability modeling is used to determine if the reliability requirements have been achieved. "Top down" and "bottom up" modeling are two methods used to estimate the reliability of a complex system, such as the CWH. The top down method uses knowledge of the system's failure modes to generate a system reliability estimate. These failure modes are identified by evaluating the system's functionality at the top level, then proceeding down to the lower level subsystems to evaluate their failure modes. The bottom up method uses knowledge of the system's component failure modes (or failure rates) to generate a system reliability estimate. These failure modes are generated by the component type and application. This document is intended to provide project managers and engineers with a systematic way to estimate the reliability of complex systems when reliability demonstration data is not available. The examples presented in this document focus on the Brooks CWH. In this document the author: 1) presents two reliability modeling methods, top down and bottom up, for developing reliability models for the Brooks CWH; 2) provides step-by-step procedures for creating these models; and 3) explains the appropriate application of these models to the CWH.