Tungsten connectors allow wires to be linked from layer to layer.
The wires become thicker in the upper layers to reduce resistance so that widely separated groups of transistors can be linked by high-speed connections. Gordon Moore, meet Georg Simon Ohm and Michael Faraday. Moore's law postulates that by continually making transistors smaller and squeezing them closer together, the number of tiny switches on a chip doubles every 18 months. But the principle of getting more for less does not apply to the wires connecting the millions of transistors that populate the fastest microprocessors. But there is no good way to shrink down the interconnections the way you can the transistors.