A vertically alternating sequence of continuous insulating layers and continuous sacrificial material layers is formed over a substrate. Memory stack structures are formed through the vertically alternating sequence. Divider trenches and slit trenches are formed such that the divider trenches laterally extend along a first horizontal direction and divide the vertically alternating sequence into a plurality of alternating stacks of insulating layers and sacrificial material layers, and the slit trenches laterally extend along a second horizontal direction that is perpendicular to the first horizontal direction. The sacrificial material layers are replaced with electrically conductive layers employing the divider trenches as a conduit for an etchant and for a reactant. Each of the divider trenches and the slit trenches are filled with material portions to provide a plurality of divider trench fill structures in the divider trenches and to provide a plurality of slit trench fill structures in the slit trenches.