Intel's Pentium processor (1993) was a complex chip for its time, with 3 layers of metal wiring over the silicon. I removed the layers, one at a time, so we can take a look at each layer... 1/n
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Transistors are the basic component of a chip; this magnified photo shows 30 of the Pentium's 3.1 million transistors. Parts of the silicon (gray) are doped with impurities, changing its properties. Doped silicon is pinkish. Thin lines of polysilicon make transistors when they cross doped silicon.
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This photo shows the first layer of metal wiring on top of the silicon, connecting the transistors together. The dark circles are contacts, connecting the wiring to the silicon or polysilicon below.
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A second layer of metal wiring distributes power and control signals. You can see some of the circuitry underneath, hazy due to the insulating oxide layer. The black circles are vias, connections to other metal layers.
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The top metal layer is thicker; it provides the main power and ground distribution through the chip (wide metal lines at sides of the photo). It also has long-distance signal lines; the lines at the top of the chip run halfway through the chip distributing floating-point data.
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It takes many steps to build up a chip layer by layer. I've shown the layers of the Pentium, from the lowest to the top. In my latest blog post, I take a close look at the circuits in the photos above: https://www.righto.com/2025/01/pentium-reverse-engineering-bicmos.html
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@kenshirriff awesome pictures! How do you remove layer by layer and how thick is one layer? Is it difficult to remove one layer without damaging the next? Sorry for the many questions, I'm amazed how this works!
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@grob I tried a variety of acids and chemicals which removed the layers, but the quality got worse for the lower layers. Then I tried sandpaper, which worked shockingly well (in small regions). The Pentium is planarized, making the layers completely flat. So I can sand through each layer cleanly.
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@kenshirriff wow, I'm so surprised sanding works! I somehow thought it'd be hard to sand parallel enough to not go across layers. Pretty cool, thanks!
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@grob The layers are more widely separated than I expected, so I don't need to be exact in my sanding. Also, I'm looking at fairly small areas of the chip, not the whole thing at once. So it's not as hard to keep it even.
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@kenshirriff I worked for a US Fab, in the engineering side (CAD guy, not design guy), and I never really understood how these structures were built. In general, sure. But I couldn't pick out a transistor from the SEM photos for anything. Your site is really educational for me.
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