Method for forming channel hole plug of three-dimensional memory device

A method for forming a channel hole plug structure in a three-dimensional (3D) memory device, comprising:

• forming an alternating dielectric stack disposed on a substrate;
• forming a first insulating layer on the alternating dielectric stack;
• forming a channel structure penetrating the first insulating layer and the alternating dielectric stack, wherein the channel structure includes a functional layer, a channel layer, and a filling structure;
• forming a second insulating layer directly on the first insulating layer and the channel structure;
• forming a hard mask layer directly on the second insulating layer;
• forming a photoresist layer directly on the hard mask layer;
• forming an opening in the hard mask layer and the photoresist layer to expose the second insulating layer, wherein a diameter of the opening in a lateral plane is larger than a diameter of a top surface of the channel structure;
• removing, using the hard mask layer or the photoresist layer as a mask, a portion of the second insulating layer above the channel structure to form a recess in the first and second insulating layers, wherein a bottom aperture of the recess exposes the top surface of the channel structure;
• forming a semiconductor layer in the recess and on the hard mask layer, wherein the semiconductor layer is formed using a same semiconductor material of the channel layer, and in contact with the channel layer;
• and
• removing the hard mask layer and a top portion of the semiconductor layer, such that a remaining portion of the semiconductor layer embedded in the first and second insulating layers forms a channel hole plug in the recess, wherein a diameter of the channel hole plug in a lateral plane is larger than the diameter of the top surface of the channel structure.