All the processes described take place inside a clean room. You may have already seen some pictures of people working inside a clean room with special clothes, called ”bunny suits“.

click to enlarge
Figure 5: Bunny suits.

Since we are talking about microscopic transistors, even the smallest particle of dust can contaminate and destroy the chip, see some examples in Figure 6.

click to enlarge
Figure 6: Even the smallest dust particle can destroy the chip.