This is the lowest level of abstraction computer, at which the basic gates and power are described.
At this level, you are basically thinking about the 3D layered structure of a chip, and how to make machines that will allow you to create better, usually smaller, gates.
Notable 2019 players in this area include companies such as:
- ASML, which makes machines to make chips
- TSMC is one of the companies that has fabs, which buys machines from companies such as ASML and puts them together in so called "silicon fabs" to make the chipsA list of fabs can be seen at: https://en.wikipedia.org/wiki/List_of_semiconductor_fabrication_plants and basically summarizes all the companies that have fabs.