Memory device and fabrication thereof

Abstract

The invention is related to a memory device, including a substrate, a capacitor which is substantially C-shaped in a cross section parallel to the substrate surface and a word line coupling the capacitor. In an embodiment, the C-shaped capacitor is a stack capacitor. Both inner edge and outer edge of the C-shaped capacitor can be used for providing capacitance.

1 . A memory device, comprising:
 a substrate;   a capacitor having a C-shaped pattern at a cross section parallel to a surface of the substrate, wherein the capacitor is a stack capacitor; and   a word line coupling the stack capacitor.   
     
     
         2 . The memory device as claimed in  claim 1 , wherein the stack capacitor is coupled to the word line through a conductive contact. 
     
     
         3 . The memory device as claimed in  claim 2 , wherein the conductive contact is formed in a dielectric layer, a stack layer comprising a C-shaped opening is disposed on the dielectric layer, and the C-shaped opening is conformally filled with a capacitor dielectric layer as the stack capacitor. 
     
     
         4 . The memory device as claimed in  claim 2 , further comprising a bit line disposed under the stack capacitor and interlaced with the word line. 
     
     
         5 . A method for forming a memory device, comprising:
 providing a substrate;   forming a capacitor overlying the substrate, wherein the capacitor has a C-shaped pattern at a cross section parallel to a surface of the substrate, and the capacitor is a stack capacitor; and   forming a word line on the substrate.   
     
     
         6 . The method for forming a memory device as claimed in  claim 5 , wherein the step of forming the C-shaped stack capacitor is performed after formation of the word line, and the step of forming the C-shaped stack capacitor comprises:
 forming a stack layer over the word line;   patterning the stack layer to form a C-shaped opening; and   forming a capacitor in the C-shaped opening.   
     
     
         7 . The method for forming a memory device as claimed in  claim 6 , wherein the step of patterning the stack layer to form the C-shaped opening comprises:
 forming a hard mask layer on the substrate;   forming a pillar structure on the stack layer;   forming a ring-shaped spacer surrounding the pillar structure;   selectively etching a portion of the ring-shaped spacer to form a C-shaped spacer;   depositing a sacrificial layer to cover the C-shaped spacer, the pillar structure and the stack layer;   polishing the sacrificial layer till the C-shaped spacer is exposed; and   removing the C-shaped spacer to form the C-shaped opening in the sacrificial layer.   
     
     
         8 . The method for forming a memory device as claimed in  claim 7 , wherein the ring-shaped spacer is formed of polysilicon and the step of selectively etching a portion of the ring-shaped spacer to form the C-shaped spacer comprises:
 performing an implanting process with a tilt-angle to implant a portion of the ring-shaped spacer; and   performing an etching process using NH4OH as a primary etchant to remove an undoped portion of the ring-shaped spacer, wherein the remaining doped portion of the ring-shaped spacer constitute the C-shaped spacer,   wherein the implanting process with the tilt-angle uses dopants of BF 2 .