Another oxide material 135 may be formed over the etch stop material 130, as shown in FIG. 2, to fill in a region overlying the stairs 125. The another oxide material 135 may be selected to be selectively etchable relative to the etch stop material 130 during formation of the contact holes 150 (see FIG. 5). The another oxide material 135 may also be selected to be selectively etchable relative to the nitride materials 120 of the tiers 110. The another oxide material 135 may be a silicon oxide or other insulative material selectively etchable to the etch stop material 130 and the nitride materials 120.

The another oxide material 135 may be planarized, such as by a chemical mechanical planarization (CMP) process, to expose an upper surface of the etch stop material 130 over an uppermost tier 110, as shown in FIG. 3. The upper surface of the etch stop material 130 may be substantially coplanar with an upper surface of the another oxide material 135.