In-line monitoring coverage visualization

In-line monitoring (ILM) is frequently used in semiconductor manufacturing to identify tool faults quickly and to minimize the impact on yield. Due to the expense of ILM only a fraction of the lots processed can be inspected. In practice process engineers devise a sampling plan to select lots for inspection so that 1) the inspection coverage, defined as the proportion of tools included in the inspection sample, is roughly equal to the tool usage and 2) all tools are covered by the inspection sample. This paper describes a new graphical display of tool usage, inspection coverage, and coverage loss that enables process engineers to quickly identify problems with the sampling plan. The displays are a graphical representation of the manufacturing process between inspection steps that show tool usage, inspection coverage, and the difference between usage and coverage.