Not entirely the same, but at each step of the semiconductor manufacturing process, the process step is run on a pool of available tools from the fleet. (Think

Not entirely the same, but at each step of the semiconductor manufacturing process, the process step is run on a pool of available tools from the fleet. (Think photolithography machines to make the pattern, etch or deposition tools, and SEMs &c for inline measurement.) These things being hardware for controlling physical and chemical processes, they're of course fickle, so even though two tools should be expected to produce the same results for the same step running the same configuration ("recipe") they unsurprisingly don't always do that. So in a given fleet maybe only 3/4 of them will be cleared to run a given recipe, and all the tools in this pool are supposed to be running the same version of the recipe. Discovering that several tools have not been running the same recipe and are producing noticeably diverging results going back weeks or months is an every-other-week sort of discovery and raising the alarm was always met with the same response—cover it up; don't make waves.