I am not an expert in this area. Most of it is physics simulations.

An example I know of is that we use feed forward control to make sure layers are aligned and printed with nanometer precision. Simulations are needed in this instance to model effects like thermal expansion, pressure waves, and much more.

There is also more work in metrology (measurement) with stuff like scanning electron microscopes, lasers, flow, etc.

You can find more about this by looking at the companies ASML has acquired or ASML's job postings.