Contact structures for three-dimensional memory device

Abstract

Embodiments of contact structures of a three-dimensional memory device and fabrication method thereof are disclosed. The three-dimensional memory structure includes a film stack disposed on a substrate, wherein the film stack includes a plurality of conductive and dielectric layer pairs, each conductive and dielectric layer pair having a conductive layer and a first dielectric layer. The three-dimensional memory structure also includes a staircase structure formed in the film stack, wherein the staircase structure includes a plurality of steps, each staircase step having two or more conductive and dielectric layer pairs. The three-dimensional memory structure further includes a plurality of coaxial contact structures formed in a first insulating layer over the staircase structure, wherein each coaxial contact structure includes one or more conductive and insulating ring pairs and a conductive core, each conductive and insulating ring pair having a conductive ring and an insulating ring.

What is claimed is: 
     
         1 . A three-dimensional memory structure, comprising:
 a film stack disposed on a substrate, wherein the film stack comprises a plurality of conductive and dielectric layer pairs, each conductive and dielectric layer pair comprising a conductive layer and a first dielectric layer;   a staircase structure formed in the film stack, wherein the staircase structure comprises a plurality of steps, each staircase step comprising two or more conductive and dielectric layer pairs; and   a plurality of coaxial contact structures formed in a first insulating layer over the staircase structure,
 wherein each coaxial contact structure comprises one or more conductive and insulating ring pairs and a conductive core,
 wherein each conductive and insulating ring pair comprises a conductive ring and an insulating ring. 
 
   
     
     
         2 . The three-dimensional memory structure of  claim 1 , wherein each conductive ring contacts the conductive layer of a corresponding conductive and dielectric layer pair of the staircase step. 
     
     
         3 . The three-dimensional memory structure of  claim 2 , wherein
 each coaxial contact structure comprises at least an outer conductive ring and an inner conductive ring; and   the outer conductive ring corresponds with an upper conductive and dielectric layer pair of the staircase step, wherein
 the outer conductive ring comprises larger diameter, and 
 the upper conductive and dielectric layer pair is farther away from the substrate. 
   
     
     
         4 . The three-dimensional memory structure of  claim 2 , wherein
 each coaxial contact structure comprises at least an outer conductive ring and an inner conductive ring; and   the inner conductive ring corresponds with a lower conductive and dielectric layer pair of the staircase step, wherein
 the inner conductive ring comprises smaller diameter, and 
 the lower conductive and dielectric layer pair is closer to the substrate. 
   
     
     
         5 . The three-dimensional memory structure of  claim 1 , wherein the conductive core contacts the conductive layer closest to the substrate in the staircase step of two or more conductive and dielectric layer pairs. 
     
     
         6 . The three-dimensional memory structure of  claim 1 , wherein
 the insulating ring of the conductive and insulating ring pair is disposed to surround a sidewall of the conductive ring and a sidewall of the conductive layer of the staircase structure, wherein the insulating ring is configured to electrically isolate the conductive ring from another conductive ring or the conductive core.   
     
     
         7 . The three-dimensional memory structure of  claim 6 , wherein the insulating ring is disposed on a sidewall of the first dielectric layer of the staircase step of two or more conductive and dielectric layer pairs. 
     
     
         8 . The three-dimensional memory structure of  claim 1 , further comprising a barrier layer, disposed between the first insulating layer and the staircase structure, and the plurality of coaxial contact structures extending through the barrier layer. 
     
     
         9 . The three-dimensional memory structure of  claim 1 , further comprising:
 a gate dielectric layer on the conductive layer, and   the conductive rings extending through the gate dielectric layer to contact the conductive layers of the staircase structure.   
     
     
         10 . A method for forming a three-dimensional memory structure, comprising:
 disposing a dielectric film stack on a substrate, wherein the dielectric film stack comprises a plurality of alternating dielectric layer pairs, each alternating dielectric layer pair comprising a first dielectric layer and a second dielectric layer different from the first dielectric layer;   forming a dielectric staircase in the dielectric film stack, wherein the dielectric staircase comprises a plurality of steps, each dielectric staircase step comprising two or more alternating dielectric layer pairs;   disposing a first insulating layer on the dielectric staircase;   forming a plurality of memory strings in the dielectric film stack;   replacing the second dielectric layers with conductive layers to form a staircase structure with a plurality of steps, wherein each staircase step comprises two or more conductive and dielectric layer pairs, each conductive and dielectric layer pair comprising a conductive layer and the first dielectric layer; and   forming a plurality of coaxial contact structures on the staircase structure.   
     
     
         11 . The method of  claim 10 , wherein forming the coaxial contact structure comprises:
 forming a conductive and insulating ring pair for each conductive and dielectric layer pair of the staircase step in the staircase structure, wherein the conductive and insulating ring pair comprises a conductive ring and an insulating ring.   
     
     
         12 . The method of  claim 11 , wherein forming the conductive ring comprises:
 forming a first contact hole to expose the conductive layer in one of the two or more conductive and dielectric layer pairs of the staircase step in the staircase structure;   disposing a conductive film on a sidewall of the contact hole and the exposed conductive layer; and   removing the conducive film and a portion of the conductive layer from a bottom of the first contact hole to form a conductive ring, wherein a bottom of the conductive ring is formed to contact the conductive layer in one of the two or more conductive and dielectric layer pairs of the staircase step in the staircase structure.   
     
     
         13 . The method of  claim 12 , wherein forming the conductive ring further comprises etching the first dielectric layer of the next conductive and dielectric layer pair. 
     
     
         14 . The method of  claim 11 , wherein forming the insulating ring comprises:
 disposing a second insulating layer in a first contact hole;   removing the second insulating layer from the bottom of the first contact hole; and   forming the insulating ring surrounding a sidewall of the conductive ring and a sidewall of the conductive layer of one of the two or more conductive and dielectric layer pairs in the staircase step in the staircase structure; and   forming a second contact hole to expose the next conductive layer in the staircase step.   
     
     
         15 . The method of  claim 10 , wherein forming the coaxial contact structure further comprises:
 forming a contact hole to expose the conductive layer closest to the substrate in the staircase step of two or more conductive and dielectric layer pairs;   disposing a conductive material to fill the contact hole; and   forming a conductive core to contact the conductive layer closest to the substrate in staircase step of two or more conductive and dielectric layer pairs.   
     
     
         16 . The method of  claim 15 , further comprising performing a planarization process to remove the conductive material outside the contact hole and form a coplanar surface. 
     
     
         17 . The method of  claim 10 , further comprising disposing a barrier layer on the dielectric staircase prior to the first insulating layer. 
     
     
         18 . The method of  claim 10 , wherein forming the plurality of dielectric staircase steps, each having two or more dielectric layer pairs, comprises:
 disposing a patterning mask on the dielectric film stack;   etching exposed portions of the dielectric film stack in a direction perpendicular to a main surface of the substrate until portions of the two or more dielectric layer pairs are removed;   trimming the patterning mask laterally, in a direction parallel to the main surface of the substrate;   repeating the etching and the trimming until a dielectric staircase step closest to the main surface of the substrate is formed; and   removing the patterning mask.   
     
     
         19 . The method of  claim 10 , wherein replacing the second dielectric layers with the conductive layers to form the staircase structure, comprises:
 forming one or more slit structure openings, extending horizontally along the dielectric staircase, wherein the slit structure openings penetrate vertically through the dielectric film stack;   removing the second dielectric layers of the dielectric staircase to form a plurality of horizontal tunnels; and   disposing the conductive layers inside the plurality of horizontal tunnels.   
     
     
         20 . The method of  claim 19 , further comprising:
 disposing a gate dielectric layer on sidewalls of the horizontal tunnels prior to disposing the conductive layer, wherein the gate dielectric layer comprises high-k dielectric material, silicon oxide, silicon nitride or silicon oxynitride.