Simply put CPUs, and all other semiconductors, are manufactured by depositing layers of metal and oxides on a semi-conductive substrate, after which the different layers will be connected with vias to form the circuit. This sounds like an easy task, but it really isn’t, especially at the scale at which the interconnecting traces are being laid. The current 0.13-micron process has a trace-width of about 1/80th the size of a human hair and individual transistor gate widths of about 80nm, that’s 1/125th the size of a human hair, so we’re talking microscopic scale manufacturing here.
It will come as no surprise that a semiconductor plant is not to be compared to a car manufacturing plant. Semiconductor plants work with nm-scale tolerances and precision, chemistry and lithography are the tools most used and clean rooms with less dust particles in the air than the cleanest operating room are where all the action is. A car manufacturing plant works with bulky and heavy items and has at best mm-scale tolerances whereas the tools most used are robots to mount or weld all the pieces together. So there’s a world of difference, manufacturing semi-conductors is easily one of the most complex and expensive tasks in the world and very few have the budget and the know-how to pull it off.
Fig 2. A close up of a 200mm wafer filled with Athlon XP CPUs, there’s about 200 of them on a single wafer.
In essence a finished wafer consists of the individual transistors being etched into the semi-conducting silicon substrate, followed-up by layers of metal, traditionally aluminum but now replaced by copper in AMD Athlon XP and Intel Pentium 4 CPUs, and oxide to connect and isolate the different layers, vias are then used to connect the transistors to the layers above and to connect the different pieces of circuitry together to finally produce a working CPU.
If we were to look at the cross-section of a CPU-core, we’d see the transistors all the way at the bottom and then subsequent layers of metal and oxide connected by vias. Generally the smallest and most critical traces are located at the bottom to connect the transistors to the rest of the circuitry, followed by interconnecting traces that connect the various parts of the circuitry and on top are the layers that route the power throughout the CPU and enable it to connect to the pins when mounted in the packaging.