How are crossing lines implemented on microchips?
It turns out that there are layers, but people sometimes skip those when talking about how a microchip works.

The process that introduces layers is called Back end of line, or BEOL.



It basically works like this:


Create the 2D chip layer using photolithography
Apply an insulating layer
Drill holes into that layer
Apply a conducting layer, also filling the created holes and create circuit paths or interconnects
Repeat those steps as often as needed and your manufacturing process and maybe other considerations such as thermal design allows