CPUs are made mostly of crystalline silicon. First, though, that silicon must be purified. This is one of the most critical steps, because even a minute trace of impurities can cause chips to fail. Once in purified form, the silicon is formed into wafers, which are simply thin sheets crystalline material.
Then, the CPU maker etches lines onto the surface of the wafer. This process is followed by the actual placing of transistors and circuits.
Then the wafer is thoroughly cleaned with chemicals to ensure there are no contaminants. And finally, the wafer is precisely cut into the many individual chips, or CPUs, which will eventually provide the horsepower for your computer.