Split Gate Non-volatile Flash Memory Cell Having A Floating Gate, Control Gate, Select Gate And An Erase Gate With An Overhang Over The Floating Gate, Array And Method Of Manufacturing

Abstract

An improved split gate non-volatile memory cell is made in a substantially single crystalline substrate of a first conductivity type, having a first region of a second conductivity type, a second region of the second conductivity type, with a channel region between the first region and the second region in the substrate. The cell has a select gate above a portion of the channel region, a floating gate over another portion of the channel region, a control gate above the floating gate and an erase gate adjacent to the floating gate. The erase gate has an overhang extending over the floating gate. The ratio of the dimension of the overhang to the dimension of the vertical separation between the floating gate and the erase gate is between approximately 1.0 and 2.5, which improves erase efficiency.

1 . A non-volatile memory cell comprising:
 a substrate of a substantially single crystalline material of a first conductivity type, having a first region of a second conductivity type, a second region of the second conductivity type, spaced apart from the first region, forming a channel region therebetween;   a select gate insulated and spaced apart from a first portion of the channel region adjacent to the first region;   a floating gate insulated and spaced apart from a second portion of the channel region; the floating gate having a first end closest to the select gate and a second end furthest away from the select gate; said floating gate having a top surface and a bottom surface opposite thereto, with said bottom surface facing the channel region, said floating gate having a tip on the top surface and at the second end;   a tunneling barrier covering said tip, said barrier for permitting charges to pass therethrough during an erase operation;   a control gate having a top surface and a bottom surface opposite thereto, with said bottom surface insulated from and facing the top surface of the floating gate; said control gate insulated and adjacent to the selected gate, said control gate having a first end closest to the select gate and a second end furthest away from the select gate;   
       wherein said second end of the control gate is closer to a vertical line aligned with the first end of the floating gate than the second end of the floating gate, whereby a portion of the top surface of the floating gate is not facing the bottom surface of the control gate;
 an erase gate having a first portion insulated and spaced apart from the second region of the substrate and having a first end separated from the second end of the floating gate, and a second portion electrically connected to the first portion, said second portion above the floating gate and insulated therefrom and adjacent to the control gate, said second portion of the erase gate shielding said tunneling barrier from the control gate, said second portion of the erase gate separated from the floating gate by a first length measured in a direction substantially perpendicular to the direction from the first region to the second region; said second portion having a second end closest to the second end of the control gate, said second portion of the erase gate having a second length measured from the second end of the second portion of the erase gate to a vertical line aligned with the first end of the first portion of the erase gate in a direction substantially parallel to the direction from the first region to the seconds region; 
 wherein said ratio of the second length to the first length is between approximately 1.0 and 2.5. 
 
     
     
         2 . The cell of  claim 1  wherein said two portions of the erase gate are monolithically formed. 
     
     
         3 . The cell of  claim 1  wherein said two portions of the erase gate are two separate portions electrically connected together. 
     
     
         4 . The cell of  claim 2  wherein said floating gate has a sharp corner, said corner being at the second end of the floating gate closest to the first portion of the erase gate. 
     
     
         5 . The cell of  claim 4  wherein the corner facilitates electron flow from the floating gate to the erase gate during the erase operation. 
     
     
         6 . The cell of  claim 2  wherein said floating gate is insulated and spaced apart from a portion of the second region. 
     
     
         7 . The cell of  claim 6  wherein the first portion of the channel region over which the select gate is insulated and spaced apart from abuts the first region. 
     
     
         8 . The cell of  claim 2  wherein said select gate is separated from the first end of the floating gate by a composite insulating material. 
     
     
         9 . The cell of  claim 8  wherein the composite insulating material is silicon dioxide and silicon nitride. 
     
     
         10 . The cell of  claim 2  wherein said select gate is separated from the first end of the floating gate by a homogeneous insulating material. 
     
     
         11 . The cell of  claim 10  wherein said homogeneous insulating material is silicon dioxide. 
     
     
         12 - 19 . (canceled)