Solid State Physics.
Some colleges actually have classes where you make a device. I worked in a semiconductor lab, but we made large area devices.
As an example thin-film Silicon is usually deposited via a gas. If you want to dope with Boron you use the gas DiBorane. If you want to dope with Phosphorous, you can use Phosphine gas. These gasses are controlled with Mass flow controllers (a device that's based on thermal conductivity). Radio Frequency causes a plasma in the reactor with a controlled pressure and the gasses break down and your left with say with phosphorous incorporated into the silicon.
Photolithography and or x-ray lithography are ways to define patterns.
There is a technique where a laser is used to trim resistors in circuits.
Metals are put down by a process called sputtering.
The wires to the chips are connected to the outside with ultrasonic wire bonders.
I can do my best in answering questions based on my solid state physics knowledge and semiconductor fabrication, although I never made a transistor.