While the way CPUs work may seem like magic, it’s the result of decades of clever engineering. As transistors—the building blocks of any microchip—shrink to microscopic scales, the way they are produced grows ever more complicated.

Photolithography

Transistors are now so impossibly small that manufacturers can’t build them using normal methods. While precision lathes and even 3D printers can make incredibly intricate creations, they usually top out at micrometer levels of precision (that’s about one thirty-thousandth of an inch) and aren’t suitable for the nanometer scales at which today’s chips are built.

Photolithography solves this issue by removing the need to move complicated machinery around very precisely. Instead, it uses light to etch an image onto the chip—like a vintage overhead projector you might find in classrooms, but in reverse, scaling the stencil down to the desired precision.

The image is projected onto a silicon wafer, which is machined to very high precision in controlled laboratories, as any single speck of dust on the wafer could mean losing out on thousands of dollars. The wafer is coated with a material called a photoresist, which responds to the light and is washed away, leaving an etching of the CPU that can be filled in with copper or doped to form transistors. This process is then repeated many times, building up the CPU much like a 3D printer would build up layers of plastic.

The Issues With Nano-Scale Photolithography

It doesn’t matter if you can make the transistors smaller if they don’t actually work, and nano-scale tech runs into a lot of issues with physics. Transistors are supposed to stop the flow of electricity when they’re off, but they’re becoming so small that electrons can flow right through them. This is called quantum tunneling and is a massive problem for silicon engineers.

Defects are another problem. Even photolithography has a cap on its precision. It’s analogous to a blurry image from the projector; it’s not quite as clear when blown up or shrunk down. Currently, foundries are trying to mitigate this effect by using “extreme” ultraviolet light, a much higher wavelength than humans can perceive, using lasers in a vacuum chamber. But the problem will persist as the size gets smaller.


Read more: https://www.howtogeek.com/403953/how-are-cpus-actually-made/

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