MY BRAIN HURTS!
With all the recent talk about new GPUs from Nvidia and AMD, not to mention the new ZEN 3 CPU from AMD, I started thinking about these "7 nm" chip fab processes. And no matter how hard I try, I end up with the fact that someone, somewhere, must have repealed the basic laws of physics because they are so far beyond the diffraction limit (like seriously, almost 2 orders of magnitude beyond) that it's making me question our reality.
So here's how I understand the process: UV light from an ArF eximer laser at 193 nm is passed through a metal mask to expose the photoresist that is applied to the wafer. This "develops" the photoresist layer wherever the UV light passes through the mask. Then they step the mask to the next position on the wafer and repeat the exposure process. When the whole wafer is done, then either the exposed or the unexposed portion of the photoresist is removed (depending on the type) which leaves parts of the bare wafer exposed. Then they deposit the P-type or N-type silicon as needed to create the transistor parts. Repeat for several layers to build up the parts of each transistor (not to mention all the interconnects) and you have a functional chip.
Here's where the laws of physics break down: the diffraction limit for 193 nm light is half the wavelength, or 96.5 nm. If you try to resolve anything smaller than that, the image gets blurry. So shining the 193 nm UV light through the mask should only be able to create patterns in the photoresist that are 96.5 nm wide, and that assumes *perfect* optics.
OK, I understand that the photoresist pattern on the chip doesn't have to be perfect, so some "blurred edges" are acceptable. Even if we assume that you can accept a 50% loss in resolution though, that still only gets you down to 48 nm. So you're still a long way away from 7 nm, and you're already at the point where the edges of your photoresist are going to look terrible, meaning that the transistor you're trying to build might end up shorting out to it's neighbor.
So how in the name of Galileo's butthole can they manage to create structures that are only 7 nm wide when the whole process relies on the optical resolution of 193 nm UV light?
Anyone?
Adam