on aluminum process, we use 5x5 with a 2x2 hole inside pattern on top metal, since the top metal can be exposed, and the probe tip diameter we use is 0.2u, this metal ring makes it very easy to probe.
however in copper process, there will must a passivation layer covering all metal on top, to prevent contamination, in that case, simply use a 5x5 copper metal squre (without a hole in it) is good enough, because you will have to carve a window on that passivation layer, than landing a probe is also fine.