eli5 How are transistors made so crazy small?
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You know how a microscope can make something really tiny look big. Now, instead of an eye to the microscope, put a film (or LCD display) and light source. And instead of the sample you’d observe, place a slice of silicon crystal – that had been put into a mist of vapor of a photo-sensitive substance.
Your film (or the display) has a blueprint of spots where all the transistors are to be on the chip. The blueprint might be pretty big actually, with the microscope’s ocular big enough. You’re now projecting the image – like cinema projector does – except instead of making it big, like in cinema, you’re making it very, very tiny. The photo-sensitive layer hardens under the light – everywhere except where the transistors need to go. Wash the crystal removing the compound from where it wasn’t hardened, and put it in vapor of a substance that penetrates into silicon turning it into the right type of semiconductor for half of the transistors. Repeat the process with a different substrate to complete the transistors. Then coat it in a metal vapor, then the photo-compound, and shine the map of all electric paths onto it. Remove compound, apply acid to remove the metal where it’s unwanted, then apply a solvent that dissolves the hardened photo-compound, and you have a chip, with the silicone crystal forming transistors where needed, and metal paths connecting them.
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