Contact structures for three-dimensional memory

Abstract

Embodiments of 3D memory structures and methods for forming the same are disclosed. The fabrication method includes disposing an alternating dielectric stack on a substrate, wherein the alternating dielectric stack having first and second dielectric layers alternatingly stacked on top of each other. Next, a plurality of contact openings can be formed in the alternating dielectric stack such that a dielectric layer pair can be exposed inside at least one of the plurality of contact openings. The method further includes forming a film stack of alternating conductive and dielectric layers by replacing the second dielectric layer with a conductive layer, and forming a contact structure to contact the conductive layer in the film stack of alternating conductive and dielectric layers.

What is claimed is: 
     
         1 . A method for forming a three-dimensional (3D) memory structure, comprising:
 disposing an alternating dielectric stack on a substrate, wherein the alternating dielectric stack comprises a plurality of dielectric layer pairs, each dielectric layer pair comprising a first dielectric layer and a second dielectric layer;   forming a plurality of contact openings in the alternating dielectric stack, comprising:
 etching N number of dielectric layer pairs, wherein N is a whole number, in the alternating dielectric stack to form a plurality of openings; 
 forming a mask to cover a first group of the plurality of openings and expose a second group of the plurality of openings; and 
 etching M number of dielectric layer pairs, wherein M is a whole number; 
   replacing the second dielectric layer with a conductive layer to form a film stack of alternating conductive and dielectric layers; and   forming a contact structure to contact the conductive layer in the film stack of alternating conductive and dielectric layers.   
     
     
         2 . The method of  claim 1 , further comprising:
 forming the second group of the plurality of openings extending through the N number of dielectric layer pairs and the M number of dielectric layer pairs; and   forming the first group of the plurality of openings extending through the N number of dielectric layer pairs.   
     
     
         3 . The method of  claim 1 , wherein the etching the M number of dielectric layer pairs comprises etching twice as many as the N number of dielectric layer pairs. 
     
     
         4 . The method of  claim 1 , wherein the forming of the contact structure comprises:
 forming a liner on a sidewall of the plurality of contact openings.   
     
     
         5 . The method of  claim 4 , wherein the forming of the liner comprises disposing an insulating material on the sidewall of the plurality of contact openings. 
     
     
         6 . The method of  claim 5 , wherein the disposing of the insulating material comprises disposing silicon oxide, silicon oxynitride, silicon nitride, amorphous carbon, or a combination thereof. 
     
     
         7 . The method of  claim 4 , wherein the forming of the contact structure further comprises:
 disposing a conductive material inside the plurality of contact openings.   
     
     
         8 . The method of  claim 7 , wherein the forming of the contact structure further comprises:
 chemical mechanical polishing to form a coplanar surface.   
     
     
         9 . The method of  claim 7 , wherein the forming of the contact structure further comprises:
 prior to disposing the conductive material, forming a contact hole inside each of the plurality of contact openings to expose the conductive layer in the film stack of alternating conductive and dielectric layers.   
     
     
         10 . The method of  claim 1 , further comprising:
 prior to the forming of the plurality of contact openings, forming a plurality of memory strings in the alternating dielectric stack.   
     
     
         11 . The method of  claim 10 , wherein the forming of the plurality of memory strings comprises:
 forming a channel hole vertically penetrating the alternating dielectric stack; and   disposing a memory film and a channel layer on a sidewall of a channel hole.   
     
     
         12 . The method of  claim 1 , further comprising:
 after the forming of the plurality of contact openings, forming a plurality of memory strings in the alternating dielectric stack.   
     
     
         13 . The method of  claim 12 , wherein the forming of the plurality of memory strings comprises:
 forming a channel hole vertically penetrating the alternating dielectric stack; and   disposing a memory film and a channel layer on a sidewall of a channel hole.   
     
     
         14 . A method for forming a three-dimensional (3D) memory structure, comprising:
 disposing an alternating dielectric stack on a substrate, wherein the alternating dielectric stack comprises 2 n  number of dielectric layer pairs, wherein n is an integer and each dielectric layer pair comprises a first dielectric layer and a second dielectric layer;   forming a plurality of contact openings by using (n+1) cycles of repetitive patterning process, wherein an i-th patterning process comprises:
 etching 2 (i−1)  number of dielectric layer pairs such that top 2 i  number of dielectric layer pairs are exposed inside the plurality of contact openings, wherein i is an integer ranging from 1 to n; 
   replacing the second dielectric layer with a conductive layer to form a film stack of alternating conductive and dielectric layers; and   forming a contact structure electrically connected to the conductive layer in the film stack of alternating conductive and dielectric layers.   
     
     
         15 . The method of  claim 14 , wherein the i-th patterning process further comprises:
 prior to the etching, forming a mask to cover a first subset of the plurality of contact openings and exposing a second subset of the plurality of contact openings, wherein top 2 (i−1)  number of dielectric layer pairs are exposed inside the second subset of the plurality of contact openings.   
     
     
         16 . The method of  claim 14 , further comprising:
 prior to forming of the plurality of contact openings, disposing a hard mask on the alternating dielectric stack; and   forming a plurality of openings in the hard mask.   
     
     
         17 . The method of  claim 14 , wherein the forming of the contact structure comprises:
 forming a liner on a sidewall of the plurality of contact openings.   
     
     
         18 . The method of  claim 17 , wherein the forming of the contact structure further comprises:
 disposing a filling material inside the plurality of contact openings.   
     
     
         19 . The method of  claim 18 , wherein the forming of the contact structure further comprises:
 forming a contact hole inside each of the plurality of contact openings to expose the conductive layer in the film stack of alternating conductive and dielectric layers.   
     
     
         20 . The method of  claim 17 , wherein the forming of the contact structure further comprises:
 disposing a conductive material inside the plurality of contact openings to form electrical contact with the conductive layer.