From what I've read beyond 1nm the copper interconnects require space for proper wiring. If things get smaller the effectiveness reduces. So, companies manufacturing these are looking into other metals like ruthenium which can scale more smaller and be as effective as present day copper.

The other thing I read was about stacking transistor components vertically on top of each other rather than flat using VTFET. This could mean they could shrink the size and yet have many tranistors on top layered.

see this - https://research.ibm.com/blog/1nm-chips-vtfet-ruthenium