Photosensor having gate-all-around structure and method for forming the photosensor

Abstract

A photosensor includes a substrate, a photo-detecting column, a gate structure, a floating node structure and a channel structure. The substrate has a first doping type. The photo-detecting column has a second doping type and is disposed in the substrate. The gate structure is disposed on the substrate in a vertical direction, and is electrically insulated from the photo-detecting column. The floating node structure is disposed on the gate structure opposite to the photo-detecting column in the vertical direction, and is electrically insulated from the gate structure. The channel structure extends through the gate structure, is electrically insulated from the gate structure, and is electrically connected to the photo-detecting column and the floating node structure.

What is claimed is: 
     
         1 . A method of forming a photosensor comprising:
 forming a photo-detecting column in a substrate having a first doping type, the photo-detecting column having a second doping type opposite to the first doping type;   forming a channel structure over the photo-detecting column;   forming a gate dielectric layer over the channel structure and the photo-detecting column;   forming a gate structure that surrounds the channel structure and that is separated from the channel structure by the gate dielectric layer;   forming a supporting structure over the gate dielectric layer and the gate structure;   removing a portion of the supporting structure and a portion of the gate dielectric layer to expose a top surface of the channel structure opposite to the photo-detecting column; and   forming a floating node structure on the supporting structure in a manner that the floating node structure is directly connected to the top surface of the channel structure.   
     
     
         2 . The method as claimed in  claim 1 , wherein forming the channel structure includes:
 forming an etch mask on a top portion of the substrate, the top portion of the substrate being disposed on the photo-detecting column; and   etching the top portion of the substrate through the etch mask to form the top portion of the substrate into the channel structure.   
     
     
         3 . The method as claimed in  claim 2 , wherein forming the channel structure further includes doping the top portion of the substrate before forming the etch mask. 
     
     
         4 . The method as claimed in  claim 1 , wherein forming the channel structure includes:
 forming a patterned mask layer on the substrate, the patterned mask layer having an opening that exposes a top surface of the substrate;   forming the channel structure in the opening, the channel structure extending from the top surface of the substrate; and   removing the patterned mask layer.   
     
     
         5 . The method as claimed in  claim 1 , wherein, after removing the portion of the supporting structure and the portion of the gate dielectric layer and before forming the floating node structure, the channel structure is doped with a dopant having one of the first doping type and the second doping type. 
     
     
         6 . The method as claimed in  claim 1  further comprising, before forming the gate dielectric layer, forming an opening that extends into the photo-detecting column,
 wherein the gate dielectric layer is formed along an inner surface of the opening and an outer surface of the channel structure to cover the photo-detecting column, and the gate structure is formed around the channel structure and fills the opening. 
 
     
     
         7 . The method as claimed in  claim 1 , further comprising forming an isolation structure in the substrate aside the photo-detecting column. 
     
     
         8 . The method as claimed in  claim 1 , wherein the gate structure is formed to have a top surface at a level lower that the top surface of the channel structure. 
     
     
         9 . A method of forming a photosensor comprising:
 forming a photo-detecting column in a substrate having a first doping type, the photo-detecting column having a second doping type opposite to the first doping type;   forming a gate structure on the photo-detecting column;   forming a channel structure penetrating through the gate structure in a manner that the channel structure is formed over the photo-detecting column and is insulated from the gate structure; and   forming a floating node structure over the channel structure in a manner that the floating node structure is directly connected to the channel structure and is insulated from the gate structure.   
     
     
         10 . The method as claimed in  claim 9 , further comprising forming a supporting structure between the floating node structure and the gate structure, such that the floating node structure is insulated from the gate structure through the supporting structure. 
     
     
         11 . The method as claimed in  claim 9 , wherein in forming the channel structure, the channel structure is formed with a portion protruding away from the gate structure such that a top surface of the gate structure is lower than a top surface of the channel structure,
 the method further comprising, before forming the floating node structure, doping the portion of the channel structure with a dopant having one of the first doping type and the second doping type.   
     
     
         12 . The method as claimed in  claim 9 , further comprising forming a gate dielectric layer between the channel structure and the gate structure, such that the channel structure is insulated from the gate structure through the gate dielectric layer. 
     
     
         13 . The method as claimed in  claim 9 , wherein in forming the channel structure, the channel structure includes a plurality of channel regions, each of which penetrates through the gate structure. 
     
     
         14 . The method as claimed in  claim 13 , further comprising forming an isolation structure in the substrate aside the photo-detecting column. 
     
     
         15 . A method of forming a photosensor comprising:
 forming a photo-detecting column in a substrate having a first doping type, the photo-detecting column having a second doping type opposite to the first doping type;   forming a channel structure over the photo-detecting column along a vertical direction   forming a gate structure over the photo-detecting column along the vertical direction in a manner that the gate structure is insulated from the channel structure, and is formed around a lower portion of the channel structure;   forming a supporting structure over the gate structure along the vertical direction in a manner that a top surface of the channel structure is exposed from the supporting structure; and   forming a floating node structure on the supporting structure along the vertical direction in a manner that the floating node structure is directly connected to the top surface of the channel structure.   
     
     
         16 . The method as claimed in  claim 15 , further comprising, prior to forming the gate structure, forming an opening in the substrate and penetrating into the photo-detecting column,
 in forming the gate structure, the gate structure being formed around the lower portion of the channel structure and filling the opening in a manner that the gate structure is insulated from the channel structure and the photo-detecting column.   
     
     
         17 . The method as claimed in  claim 16 , further comprising, prior to forming the gate structure and after forming the channel structure and the opening, forming a gate dielectric layer along an inner surface of the opening and an outer surface of the channel structure to cover the photo-detecting column such that the gate structure is formed to be insulated from the channel structure and the photo-detecting column through the gate dielectric layer. 
     
     
         18 . The method as claimed in  claim 15 , wherein the photo-detecting column includes multiple regions that are spaced apart from each other, and the channel structure includes multiple channel regions that are respectively formed over the multiple regions of the photo-detecting column. 
     
     
         19 . The method as claimed in  claim 18 , wherein the floating node structure includes multiple regions that are respectively and directly connected to the multiple channel regions of the channel structure. 
     
     
         20 . The method as claimed in  claim 18 , further comprising forming an isolation structure in the substrate between two adjacent ones of the multiple regions of the photo-detecting column.