In advanced technology nodes, BEOL interconnect stack geometry has become a key lever for design enablement. The rapid increase of interconnect RC leads to not only performance loss from interconnect delay increase, but circuit power and area degradation as well. Thus, optimization of BEOL dimensions (i.e., wire width, spacing and thickness subject to a given layer’s pitch constraint) is crucial to achieve better product performance, power and area. However, it is not obvious how to optimize BEOL dimensions, especially in sub-10nm nodes. In this work, we study BEOL interconnect stack geometry by exploring wire aspect ratio (AR) and wire line-space duty cycle (DC). We perform SPICE-based analyses of timing path delays to find delay- or power-optimal (AR,DC) combinations, and also perform block-level studies with placed and routed designs. Based on our experimental results, we provide various insights on BEOL stack geometry: (i) optimal (AR,DC) for a given wire pitch with respect to power and delay; (ii) sensitivities of optimal (AR,DC) to circuit parameters (e.g., driver strength, input slew, output load, wirelength); and (iii) optimal (AR,DC) when multiple interconnect layers are considered.