Litho clusters with integrated metrology: the next step in continuous flow manufacturing

Abstract

While integrated circuit manufacturing has demonstrated continuous productivity improvement over the last twenty years (as driven by Moore's Law), there remain significant areas for improvement. The lithographic tools in current factories have set the example in productivity improvement. They have evolved from individual tools for vapor prime, coat, expose, bake operations to integrated exposure tools and photoresist tracks that handle wafers sequentially from a load port until they return to the same load port. This paper examines the next logical step in this evolution resulting in the formation of a lithography (Litho) cluster by adding metrology for critical dimension (CD) and overlay measurements and optical inspection. Since with sampling of selected sites and wafers, CD and overlay measurements are relatively quick processes, one or more lithography photocells (exposure tool and photoresist track combinations) could be integrated to one set of centrally located metrology tools. Alternatively, simpler and smaller metrology modules could be integrated into each Litho cluster tool. Since the load ports and robotics could be shared and the total number of metrology tools in the factory is expected to increase dramatically, cost reduction and economies of scale in this combination of tools may be achieved. The benefits are estimated to be a 20% improvement in cycle time and simplified material handling.