Simulation is all about using the simplest possible modeling technique that gives enough accuracy to make the results useful. Simplicity typically speeds up simulation – and, in many cases, makes the problem tractable in the first place.
But at some point, the unnecessary details that the modeling abstractions hide become necessary. At that stage, if you’re lucky, you can tweak your modeling technique to allow for the now-important effects. But eventually you may to have to take a new approach.
This is what’s happened for certain very specific processes that Coventor’s SEMulator3D tool models. Their voxel approach still works for most processes, but can’t capture all the nuances of multi-etch and selective epitaxy processes. For example, in multi-etch, where multiple materials are being etched in one step, the vertical etch rates work just fine with voxels, but they can’t capture lateral bias. For selective epitaxy, crystal orientation can affect growth rates; again, this isn’t modeled well by voxels.
So they’ve added a “surface evolution” option – a completely different mathematical approach to modeling those processes. It handles multi-etch, improves the epitaxy modeling that they introduced last year, and also introduces redeposition (where etching results in deposition of the etched material elsewhere, particularly used for sidewalls) and sputtering.
They have also introduced virtual metrology capabilities that mirror the in-line process metrology that would normally be built into a physical fabrication line. This allows monitoring of critical parameters as the process is simulated just as would be done if the experiments being simulated were actually being done on physical wafers in a real fab.
You can find out more about the latest SEMulator3D version, which they say is the biggest release they’ve ever done, in their announcement.