![]() ![]() Those parameters can then be the focus of further refinement and optimization. It turns out that SEMulator3D has an Identify Important Parameters feature that can be used based on the results of a comprehensive design of experiments (DoE). So we’re not talking about running all parameters in all possible combinations to optimize things we’ll be selective. Some of those parameters are independent of others, some are correlated with each other, and some are more important than others. You might widen or narrow it, or you might shift it a bit to move the center, or you might do some of all of the above.Įven with that, though, there are still tons of parameters over the entire processing lifetime of a wafer. With that in hand, it raises the possibility of tweaking the specified process window to improve yields. So you live with what you have.īut the thing with SEMulator3D is that it can do virtual processing of wafers. It’s just that you don’t want to commit the wafers and time to dial it in even better. ![]() But you might not have specified the optimal – i.e., actual – window, but rather one that simply works OK. So you try to do enough to get a good bead on the window and launch. So we’ve been doing it for decades using experiments to figure out where the window edges are.īut that takes a lot of wafers (read “money”) and time (OK, also read “money”). To be clear, determining a process window isn’t new it’s been a thing since processing got started, and it’s not a notion unique to semiconductors. That’s a question that Coventor has set out to answer in their latest release of their SEMulator3D tools (version 8.0). Question is, how do you know what “just right” is? Another way of asking the question is, “What’s the actual window?” So it’s a Goldilocks thing: the specified window has to be just right. On the other hand, if you specify the window to be narrower than it has to be, well, then you’re just being difficult. If you specify the window to be wider than the actual window allows, then you’re going to have yield problems for those lots processed within the specified window but on the fringes or outside the actual window. If the window is too narrow, then you’re spending all your time trying to thwart that variation and keep the equipment in the straight and narrow.īut, to be clear, there’s the actual window, which you would like to be wide, and then there’s the specified window, which you would like to be… right. It’s best if you can have a wide window, because then you can tolerate lots of variability. Go outside that range, and a die – or a wafer – or a lot – may fail. For anyone new to the concept, the window is the range of variation that’s allowable for a given process parameter. ![]() One of the tricky bits when launching a new process is figuring out what the process window is. ![]()
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