A microelectronic device includes a stack structure comprising blocks separated from one another by dielectric slot structures and each including a vertically alternating sequence of conductive structures and insulative structures arranged in tiers. At least one of the blocks comprising a stadium structure comprising opposing staircase structures each having steps comprising edges of the tiers; and a filled trench vertically overlying and within horizontal boundaries of the stadium structure of the at least one of the blocks. The filled trench includes a dielectric liner material on the opposing staircase structures of the stadium structure and on inner sidewalls of the two bridge regions and at least one dielectric structure doped with one or more of carbon and boron on the dielectric liner material, the at least one dielectric structure horizontally overlapping the steps of the stadium structure.