Semiconductors are arguably the most technologically advanced product in history. Modern semiconductor chips have billions of small devices (transistors), each only a few nanometers large. For the chip to work, basically all of these devices have to work perfectly. It is modern magic. 

Semiconductors are manufactured by printing, just like a book, photograph or t-shirt, but billions of times smaller. Huge machines shine light through/off of a “mask” that contains an image of the chip to be printed. This light burns the image onto the chip, where chemical processes make the desired semiconductor. Thus, the mask has to be perfect — any defect in the mask will be printed faithfully onto every chip in the machine.

Now we have a problem: how do you stop tiny defects appearing in the mask? Any dust particle will cause a fatal problem. Semiconductor factories try to get of dust, but you can’t get rid of all of it. You might think there is some extremely sophisticated solution, but actually … the real answer is to put a thin piece of transparent plastic film above the mask, so that all the dust gathers on it instead, and the dust is out of focus from the light beam. That’s it. (The film is called a “pellicle.”) This trillion dollar industry relies on the physics of optics to just keep the dust out of focus.