Method of making mosfet by multiple implantations followed by a diffusion step

Abstract

A short channel metal oxide semiconductor transistor device is processed without undesirable short channel effects, such as V T falloff and with a reasonable source-drain operating voltage support. In a substrate lightly doped with P-type conductivity material and source and drain region heavily doped with an N-type conductivity material, two lightly doped N- regions are disposed between the edge of the gate and the source and drain regions. A channel region is more heavily doped with P-type material than the substrate. Two regions extend from opposite sides of the channel region to an area generally below the two N- regions and above the substrate, which regions are more heavily doped than the channel regions.

What is claimed is: 
     
       1. A method for manufacturing a metal oxide semiconductor transistor device comprising: providing a semiconductor substrate of a first conductivity type;   forming a first insulating layer of silicon dioxide on an active surface of the substrate;   implanting ions of a first conductivity type into said substrate;   depositing a layer of polysilicon on said first insulating layer;   implanting ions of a second conductivity type through said polysilicon layer;   growing a second region of silicon dioxide, said silicon dioxide region being grown over said polysilicon layer;   placing a photoresistive mask over said second oxidation layer for forming a gate of the semiconductor device;   etching a predetermined portion of said second oxidation layer;   plasma etching said polysilicon layer;   removing a predetermined portion of said polysilicon layer underneath said second silicon dioxide layer;   .[.etching said second layer of silicon dioxide;.].   stripping said photoresist area from said second oxidation layer;   implanting ions of the second conductivity type;   .[.implanting ions of the first conductivity type;.].   etching said second layer of silicon dioxide overhanging said polysilicon gate layer;   .[.etching said first layer of silicon dioxide surrounding said polysilicon gate layer;.].   implanting ions of said first conductivity type;   implanting ions of said second conductivity type;   diffusing the implanted ions into said substrate; and   oxidizing the active surface of said substrate, including said polysilicon gate.   
     
     
       2. The method of making a metal oxide semiconductor transistor device of claim 1, wherein the implantation of ions of the first conductivity type are boron ions and the implantation of ions of the second conductivity type are arsenic ions. .Iadd. 
     
     
       3.  A method for forming an MOS transistor comprising the steps of providing a silicon wafer of p-type,   forming a gate oxide layer over the top surface of the wafer,   implanting acceptor ions non-selectively into the top surface of the wafer,   depositing a polysilicon layer over the gate oxide layer,   oxidizing the top surface of the polysilicon layer to form a polyoxide layer,   depositing a layer of photoresist over the polysilicon layer and patterning the photoresist to leave a selected portion overlying the polyoxide layer,   using a selected portion of the photoresist while etching the polyoxide layer and the polysilicon layer and undercutting the polyoxide layer a prescribed amount,   implanting donor ions selectively into the wafer using the polyoxide layer and the polysilicon layer as a mask,   removing the polyoxide layer from the top surface of the polysilicon layer,   implanting donor and acceptor ions selectively into the wafer using the polysilicon layer as a mask, and   heating the wafer for diffusing the implanted acceptor ions deeper into the wafer than the implanted donor ions. .Iaddend. .Iadd.   
     
     
       4.  The process of claim 3 in which the acceptor ions implanted are boron ions and the donor ions implanted are arsenic ions. .Iaddend. .Iadd.5. The process of claim 3 which includes the further steps of providing separately a gate connection to the polycrystalline layer, and source and drain connections to the donor-rich surface layer portions adjacent to the acceptor-rich region underlying the polycrystalline layer. .Iaddend. .Iadd.6. The method of claim 3 wherein the implantation of ions of the first conductivity type are boron ions and the implantation of ions of the second conductivity type are arsenic ions. .Iaddend. .Iadd.7. A method for manufacturing a metal oxide semiconductor transistor device characterized in that it comprises the following steps: providing a semiconductor substrate (12) of a first conductivity type,   forming a first insulating layer (40) of silicon dioxide on an active surface of the substrate,   implanting (42) ions of a first conductivity type into said substrate,   depositing a layer (14) of polysilicon on said first insulating layer,   implanting ions of a second conductivity type in said polysilicon layer,   growing a second region (46) of silicon dioxide, said silicon dioxide region being grown over said polysilicon layer,   placing a photoresistive mask (44) over said second silicon dioxide region   etching a predetermined portion of said second dioxide region and plasma etching said polysilicon layer; to leave a double layer of silicon dioxide and polysilicon longer than desire for the gate,   removing a predetermined portion of said polysilicon layer underneath said second silicon dioxide layer to realize the polysilicon gate (14)   stripping the photoresist mask from said second silicon dioxide layer leaving a portion of the second layer of silicon dioxide overhanging said polysilicon gate   implanting (50) ions of the second conductivity type by using said second layer of silicon dioxide as a mask for forming heavily doped regions   etching said second layer (46) of silicon dioxide overhanging said polysilicon gate layer   implanting (52) ions of said second conductivity type for forming lightly doped regions between the gate region and the heavily doped regions   implanting (54) ions of said first conductivity type for forming doped regions under the edges of the gate   diffusing the implanted ions into said substrate, and oxidizing the active surface of said substrate, including said polysilicon gate. .Iaddend.