Methods of forming microelectronic devices including staircase structures, and related microelectronic devices

A microelectronic device, comprising:

• a stack structure comprising a vertically alternating sequence of conductive material and insulative material arranged in tiers;
• a staircase structure within the stack structure and having steps defined by edges of the tiers;
• an etch-selective liner on the steps of the staircase structure and comprising a different material than each of the conductive material and insulative material;
• and
• conductive contacts within a horizontal area of the staircase structure, each of the conductive contacts comprising:
• a first portion vertically extending completely through the etch-selective liner and the stack structure;
• and
• a second portion outwardly horizontally projecting from and unitary with the first portion, the second portion in physical contact with each of a section of the etch-selective liner and the conductive material of one of the tiers directly vertically underlying the section of the etch-selective liner.

A method of forming a microelectronic device, comprising:

• forming a preliminary stack structure comprising a vertically alternating sequence of insulative material and sacrificial material arranged in preliminary tiers;
• forming a staircase structure having steps comprising edges of at least some of the preliminary tiers of the preliminary stack structure;
• forming an etch-selective liner on the steps of the staircase structure and formulated to have etch selectivity relative to the insulative material and the sacrificial material during mutual exposure to an etchant;
• forming an opening within a horizontal area of the staircase structure, the opening comprising:
• a first portion extending vertically through each of the etch-selective liner and the preliminary stack structure;
• and
• a second portion in communication with and outwardly horizontally projection from the first portion, an outer horizontal boundary of the second portion partially defined by side surfaces of the etch-selective liner and the sacrificial material of one of the preliminary tiers directly vertically adjacent to the etch-selective liner;
• replacing the sacrificial material of the tiers the preliminary stack structure with conductive material;
• and
• forming a conductive contact within the opening.