Wafer Fabrication or Wafer Fab is actually a complex proceedure of many repeated sequential processes to produce complete electrical/photonic circuits, such as radio frequency (RF) amplifiers, central processing units (CPU's) for computers, LEDs and optical computer components, and much more of our electronic control circuits, to build components with the necessary electrical structures.
The main process begins with engineers designing the circuit and defining its functions, signals, inputs, outputs and voltages needed. These electrical circuit specifications are entered into 'SPICE' like electrical circuit design programs and then imported into computer aided design CAD like circuit layout programs, so the layers can be defined for wafer mask production. The resolution of the circuits defined on the wafers is currently in the low to sub-micrometre realm and decreasing rapidly, with a resulting increase in circuit density for a given area.
The blank pure silicon wafers have circuits 'built-up' in layers in
"clean rooms", with the undesired areas to be 'etched away' by using photo-sensitive resist patterns, being photo masked in micrometre detail, onto the wafers surface. The wafers are then exposed to short-wave UV light and the unexposed areas being etched away, cleaned and then the desired areas deposited by hot chemical vapors and baked in high heat to permiate into the desired zones, or implanted w/RF energy so the needed chemicals are left in detailed patterns, defined by the original masks.
These steps can be repeated many hundreds of times depending on the complexity of the desired circuit and its connections.
There are new processes to accomplish each of these steps with better resolution and in improved ways emerging every year. This is how "Moore's Law" is seemingly being followed and new more dense and complex circuits are being produced than in previous years, for the many needs of industry and human entertainment.
A "Foundary" is where these processes are accomplished, such as those wafer fab plants owned by AMD, Intel, Texas Instruments, Motorola and many more world-wide.