Physical Vapor Deposition (PVD) systems are widely used in the semiconductor fabrication industry, both for front-end applications in the wafer fab and for back-end applications at device packaging houses. In fan-out wafer level packaging (FOWLP), and in fan-out panel level packaging (FOPLP), sputter deposited Ti and Cu are the base on which electroplated copper Redistribution Layers (RDLs) are built. For these RDL barrier/seed layers, PVD cluster tools, wafer transport architectures that have been widely used since the mid-1980s, are the current Process of Record (POR) in advanced packaging; however, these tools typically operate in a regime where wafer transport is robot-limited to approximately 50 wafers per hour, which limits overall throughput and greatly influences Cost of Ownership (COO) for the sputter deposition step(s), because the central handling robot occupied with a transfer from the Ti PVD module to the Cu PVD module, for example, has no opportunity to be doing anything other than that specific transfer.
Other wafer transport architectures are more efficient from a wafer handling perspective. In linear transport carrier-based PVD tools, wafers or panels passing through the system benefit from a mechanical transfer time budget that is considerably less than for a cluster tool. Transport time overhead per wafer on linear transport systems is quite low, and scheduler software optimization becomes less onerous too, as a result of the simpler wafer transport architecture.
We analyzed the relative throughput of cluster and linear transport PVD tools for a typical FOWLP barrier/seed layer (1000Å Ti / 2000Å Cu) sputter deposition process, and present details here of how the time spent moving wafers to various processing chambers affects overall system productivity. In the case of the cluster tool architecture, with its central wafer handling robot, wafer throughputs are approximately 50 wafers per hour, while on the linear transport system wafer throughputs as high as 240 wafers per hour are possible. The significant difference in system throughputs greatly affects the relative Cost of Ownership (COO) per wafer processed, with the linear transport system returning COO results that are less than half those of the typical cluster PVD tool.
