A semiconductor device structure that comprises tiers of alternating dielectric levels and conductive levels and a carbon-doped silicon nitride over the tiers of the staircase structure. The carbon-doped silicon nitride excludes silicon carbon nitride. A method of forming the semiconductor device structure comprises forming stairs in a staircase structure comprising alternating dielectric levels and conductive levels. A carbon-doped silicon nitride is formed over the stairs, an oxide material is formed over the carbon-doped silicon nitride, and openings are formed in the oxide material. The openings extend to the carbon-doped silicon nitride. The carbon-doped silicon nitride is removed to extend the openings into the conductive levels of the staircase structure. Additional methods are disclosed.