Fabrication on the wafer

6.1 · The photolithography build cycle (repeats many times)

Steps 3–5 describe what a transistor is; fabrication is how millions are printed on the wafer at once, photographically. A single layer is built by a repeating cycle: deposit a thin film, coat it with light-sensitive photoresist, expose it to UV through a patterned mask (photolithography), etch away the unwanted film, implant dopant ions to form the N+/P+ regions, and add metal wiring. This cycle repeats for dozens of stacked layers, with features only a few nanometres wide.

6.2 · Parallelism & yield: hundreds of dies per wafer

Because every step happens across the whole wafer at the same time, hundreds of identical chips (dies) are made together. The full process can take 500+ steps over several weeks, in cleanrooms far purer than an operating theatre, since one dust speck can kill a die. The fraction of dies that work is called the yield; good ones are kept and defective ones discarded.