I understand the basic of chip manufacturing, you have a stencil with the chip in "big" size, you illuminate it, it goes through a lens to hit the wafer with pre applied photo sensible material.

Now, modern CPU have billions of transistors and it raised a few questions I was unable to answer properly after a few researches online.

- How is the chip designed, I mean, "placing" a billion transistors by hand is not feasible, so how does it works to create the design and simulate it?

- When the design is ready, how are stencils built? Even using lasers, engraving billions of traces seems unreal. Is there another technique used?

- If we consider we have the stencil, how are the different materials created with such high precision? How can the distance between the lens and the table be adjusted with so much precision? There must be a trick. The lens has to be ultra precise, the wafer perfect... I mean, we are speaking of a few nanometers in required precision, or I must be missing something.

My general understanding is quite well summarized in this article: https://www.geek.com/chips/from-sand-to-hand-how-a-cpu-is-made-832492/