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Simulating the Whole Process

Back when discussion CMOS-compatible MEMS, I briefly mentioned a couple tools from Coventor that are used in MEMS design. But one of them actually has use for any semiconductor process. You might think it’s another TCAD tool, but actually, it isn’t.

TCAD tools work with low-level physics to model small portions of an overall process. It’s like using SPICE to simulate a cell – very detailed, but can’t be used on an entire circuit. Likewise, you typically wouldn’t run a TCAD tool across an entire process from start to finish.

That’s what Coventor’s SEMulator3D does. It’s abstracted up one layer, and can be used to animate – literally – the entire process of building a transistor or other device. They do this using “voxels” – the 3D equivalent of a pixel. The sides of a voxel are sized so that there are 2-4 of them within the minimum feature size. The properties of each voxel include materials information, and there can be mixes and gradients so that there’s no pretense of a particular volume consisting of only one material.

Throughout the steps of the process, voxels are added (e.g., deposition), modified (e.g., implant), or deleted (e.g., etch). Some chemical interactions can be modeled (for example, if you ended up etching something you hadn’t intended); some can’t (for example, if copper is on bare silicon, resulting in electromigration). All of the effects are correlated with actual silicon.

The process description input to the tool is separate from the layout of a given circuit, so you can develop a “regression suite” of layouts. When you want to consider a process change, you can then apply it across the suite to see if it causes any problems in any of them. It can support layouts containing even thousands of transistors.

Their recent news is that they’ve now released a 64-bit version. This allows bigger areas to be simulated, or the use of smaller voxels – important as dimensions continue to shrink.

You can find more in their release

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