Wafers are already 3D. It's just that all the dozen or so metal layers are used to route signals and power. Only the critical few layers for the transistors themselves are fabricated using the latest nodes. https://en.wikichip.org/wiki/File:intel_interconnect_10_nm.jpg
TheseusPankration t1_j0aci3b wrote
Reply to comment by orincoro in Japan to Manufacture 2nm Chips With a Little Help From IBM by Avieshek
Wafers are already 3D. It's just that all the dozen or so metal layers are used to route signals and power. Only the critical few layers for the transistors themselves are fabricated using the latest nodes. https://en.wikichip.org/wiki/File:intel_interconnect_10_nm.jpg