Double blanket ion implant method and structure

Abstract

A double blanket ion implant method for forming diffulsion regions in memory array devices, such as a MOSFET access device is disclosed. The method provides a semiconductor substrate with a gate structure formed on its surface Next, a first pair of diffulsion regions are formed in a region adjacent to the channel region by a first blanket ion implantation process. The first blanket ion implantation process has a first energy level and dose. The device is subjected to oxidizing conditions, which form oxidized sidewalls on the gate structure. A second blanket ion implantation process is conducted at the same location as the first ion implantation process adding additional dopant to the diffusion regions. The second blanket ion implantation process has a second energy level and dose. The resultant diffusion regions provide the device with improved static refresh performance over prior art devices. In addition, the first and second energy levels and doses are substantially lower than an energy level and dose used in a prior art single implantation process.

1 - 39 . (canceled)  
   
   
       40 . A method for forming a semiconductor device, said method comprising: 
 forming a gate structure having sidewalls over a semiconductor substrate;    performing a first blanket implant with a first dopant on said substrate to form a plurality of first diffusion regions adjacent to the sidewalls of said gate structure;    performing a re-ox to oxidize at least a portion of sidewalls of said gate structure; and    performing a second blanket implant with a second dopant on said substrate to form a plurality of second diffusion regions, each of said second diffusion regions being formed within a space previously occupied by a respective one of said plurality of first diffusion regions;    wherein 
 each of said first diffusion regions is associated with and located beneath a respective second diffusion region;  
 each of said first diffusion regions includes a portion extending beneath said gate structure; and  
 none of said plurality of second diffusion regions include any portion which extends beneath said gate structure.  
   
   
   
       41 . The method of  claim 40 , wherein said first dopant is a n-type dopant.  
   
   
       42 . The method of  claim 41 , wherein said first dopant is chosen from a group consisting of phosphorous, arsenic, and antimony.  
   
   
       43 . The method of  claim 40 , wherein said first dopant is a p-type dopant.  
   
   
       44 . The method of  claim 43 , wherein said first dopant is chosen from a group consisting of boron, boron bifloride, and borane.  
   
   
       45 . The method of  claim 40 , wherein said first blanket implant is performed using an energy level ranging between 5 KeV to 45 KeV.  
   
   
       46 . The method of  claim 45 , wherein said first blanket implant is performed using an energy level of 15 KeV.  
   
   
       47 . The method of  claim 40 , wherein said first blanket implant is performed using an dosage ranging between 1×10 12  ions/cm 2  to 7×10 12  ions/cm 2 .  
   
   
       48 . The method of  claim 47 , wherein said first blanket implant is performed using a dosage of 2×10 12  ions/cm 2 .  
   
   
       49 . The method of  claim 40 , wherein said second dopant is the same as said first dopant.  
   
   
       50 . The method of  claim 40 , wherein said second dopant is different from said first.  
   
   
       51 . The method of  claim 50 , wherein said second dopant is of a different conductivity type as said first dopant.  
   
   
       52 . The method of  claim 40 , wherein said second blanket implant is performed using an energy level ranging from 5 KeV to 60 KeV.  
   
   
       53 . The method of  claim 52 , wherein said second blanket implant is performed using an energy level of 20 KeV.  
   
   
       54 . The method of  claim 40 , wherein said second blanket implant is performed using a dosage ranging from 1×10 12  ions/cm 2  to 10×10 12  ions/cm 2 .  
   
   
       55 . The method of  claim 54 , wherein said second blanket implant is performed using a dosage of 4×10 12  ions/cm 2 .  
   
   
       56 . A method of forming a semiconductor device, comprising: 
 providing a gate structure disposed over a surface of said semiconductor substrate;    performing a first blanket implant into the substrate to form a plurality of diffusion regions underneath the surface of the substrate adjacent to the gate structure, with a portion of each diffusion regions extending underneath a portion of said gate structure, thereby forming respective first and second overlap regions;    performing a re-ox step to form oxidized sidewalls on the gate structure and oxide regions on the substrate; and    performing a second blanket implant through the oxide regions and into the substrate at locations of the first and second diffusion regions to add additional dopant to the first and second diffusion regions, wherein the oxidized sidewalls on the gate structure prevents the additional dopant from diffusing underneath the gate structure, thereby forming respective diffusion regions on opposite sides of the gate structure each having a graded dopant concentration.    
   
   
       57 . The method of  claim 56 , wherein said first dopant is chosen from a group consisting of: phosphorous, arsenic, and antimony.  
   
   
       58 . The method of  claim 56 , wherein said second dopant is chosen from a group consisting of: phosphorous, arsenic, and antimony.  
   
   
       59 . The method of  claim 56 , wherein said first dopant is chosen from a group consisting of: boron, boron bifloride, and borane.  
   
   
       60 . The method of  claim 56 , wherein said second dopant is chosen from a group consisting of: boron, boron bifloride, and borane.