--- (---.delete@this.redheron.com) on June 13, 2022 9:11 pm wrote:
>
> The distinction between contacts and layers is a reasonable point, but is it significant?
> Is there an interest/important reason why it's more difficult to create a layer of cobalt traces
> than to create short vertical contacts of cobalt? I guess there is *some* difference given that
> tungsten has frequently been used for these sorts of plugs, but I'd love to know the full story.


The distinction is very significant.

Already since the beginning there were speculations that the cobalt interconnections may have a too large resistance, and that TSMC might be wiser by using cobalt only for contacts, instead of using it for traces, like Intel.

This has been confirmed now by the Intel presentation, where the figure comparing the interconnection metals used in Intel 4 and Intel 7 shows good reliability but bad resistance for the cobalt interconnections.


A cobalt contact has a small resistance, because it is very short and it is also wider than its length.

A cobalt trace on the other hand, introduces a much greater resistance, because it is long and narrow.