Staircase formation in three-dimensional memory device

A method for forming a 3D memory device, comprising:

• forming an alternating layer stack over a substrate;
• removing a first number (M) of layer stacks of the alternating layer stack over a first portion of a surface of the alternating layer stack, wherein M is greater than one;
• and
• forming staircase structures over a second portion of the surface of the alternating layer stack, wherein the second portion of the surface includes the first portion of the surface and each of the staircase structures has M steps in a first direction, wherein each of the M steps is one level, exposing a portion of a surface of a layer stack of the alternating layer stack.

A 3D memory device, comprising:

• an alternating layer stack disposed over a substrate;
• a storage structure comprises a plurality of vertical semiconductor channels;
• a first staircase regions adjacent to the storage structure;
• a second staircase regions adjacent to the storage structure, wherein the second staircase regions are horizontally separated from the first staircase regions by the storage structure;
• and
• a staircase structure disposed at each of the first and the second staircase regions to expose a portion of a plurality of layer stacks of the alternating layer stack, wherein the staircase structure comprises a plurality of steps in a first direction and a first number (M) of steps in a second direction, wherein each of the steps in the first direction has 2M levels.