Dual gate oxide process for deep submicron ICS

Abstract

An improved dual gate oxide process for dual-gated devices using oxygen ion implantation to vary the thickness of gate oxide layers. The desired layers are identified by photoresist layer patterning prior to an ion implantation. A subsequent heat treatment oxidizes the implanted region.

What is claimed is:  
     
         1 . A method of forming gate oxide layers of different thicknesses on an integrated circuit device which comprises the steps of: 
 (a) growing a gate oxide layer on the device;    (b) applying a photoresist mask layer over the oxide layer;    (c) removing the photoresist mask where thicker oxide areas are desired;    (d) performing an oxygen ion implantation on the surface of the device;    (e) cleaning off the photoresist layer; and,    (f) heating the device to oxidize the implanted silicon.    
     
     
         2 . The method of  claim 1  wherein the oxygen ion implantation of step (d) is accomplished using oxygen plasma in a magnetic field.  
     
     
         3 . The method of  claim 1  wherein the oxide layer of step (a) is in the approximate range of about 35 Angstroms to about 55 Angstroms thick.  
     
     
         4 . The method of  claim 1  wherein the oxygen ion implantation of step (d) is performed using an accelerating voltage in the approximate range of about 200 eV to about 800 eV.  
     
     
         5 . The method of  claim 2  wherein the magnetic field is generally in the range of about 1 gauss to about 100 gauss.  
     
     
         6 . The method of  claim 1  wherein the resulting peak range of implanted ions is in the approximate range of about 20 Angstroms to about 50 Angstroms with a range straggle of about 10 Angstroms to about 25 Angstroms.  
     
     
         7 . The method of  claim 1  wherein the heating of step (f) occurs in the range of about 400° C. to about 600° C. for a time period in the range of about 30 minutes to about 120 minutes.  
     
     
         8 . The method of  claim 1  wherein the gate oxide of step (a) is a nitrided gate oxide.  
     
     
         9 . A method of forming gate oxide layers of different thicknesses on a metal oxide semiconductor device having a layer of gate oxide, the method comprising the steps of: 
 (a) applying a patterned photoresist layer over the oxide layer;    (b) performing an oxygen ion implantation on the surface of the integrated circuit;    (c) cleaning off the photoresist layer; and,    (d) heating the device to oxidize an ion implanted layer.    
     
     
         10 . The method of  claim 9  wherein steps (a) through (d) are performed sequentially at least twice.  
     
     
         11 . The method of  claim 9  wherein oxygen ion implantation of step (b) is accomplished using oxygen plasma in a magnetic field.  
     
     
         12 . The method of  claim 9  wherein the oxygen ion implantation of step (b) is performed using an accelerating voltage in the appropriate range of about 200 eV to about 800 eV.  
     
     
         13 . The method of  claim 11  wherein the magnetic field is generally in the range of about 1 gauss to about 100 gauss.  
     
     
         14 . The method of  claim 10  wherein the resulting peak range of implanted ions is in the approximate range of about 20 Angstroms to about 50 Angstroms with a range straggle of about 10 Angstroms to about 25 Angstroms.  
     
     
         15 . The method of  claim 9  wherein the heating of step (f) occurs in the range of about 400° C. to about 600° C. for a time period range of about 30 minutes to about 120 minutes.  
     
     
         16 . A metal oxide semiconductor device comprising: 
 a thin oxide gate region;    a thick oxide gate region, and wherein said thick oxide gate region comprises oxidized oxygen ions implanted into said thick oxide gate region and oxidized by heat treatment.    
     
     
         17 . The device of  claim 16  wherein the thin oxide gate region is in the approximate range of about 35 Angstroms to about 55 Angstroms thick.  
     
     
         18 . The device of  claim 15  wherein the thick oxide gate region is in the approximate range of about 40 Angstroms to about 90 Angstroms thick.  
     
     
         19 . The device of  claim 16  wherein the first gate oxide layer comprises a nitrided gate oxide.  
     
     
         20 . A metal oxide semiconductor device comprising: 
 a first oxide gate layer;    a region covered by said first oxide gate layer which has been implanted by oxygen ions and subsequently heat treated, thus comprising a second gate oxide layer.    
     
     
         21 . The device of  claim 20  wherein the first oxide gate layer is in the range of about 35 Angstroms to about 55 Angstroms thick.  
     
     
         22 . The device of  claim 18  wherein the second gate oxide layer is in the range of about 40 Angstroms to about 90 Angstroms thick.  
     
     
         23 . The device of  claim 18  wherein the first gate oxide layer comprises a nitrided gate oxide  
     
     
         24 . A method for forming gate oxide on a substrate, the method comprising: 
 forming a gate oxide layer on the substrate;    selectively forming a photoresist layer over the gate oxide, wherein a portion of the gate oxide layer remains exposed to form an exposed portion;    introducing oxygen ions into the exposed portion;    oxidizing the substrate, wherein the exposed portion of the gate oxide layer is thicker than other portions of the gate oxide layer.    
     
     
         25 . The method of  claim 24  wherein the oxidizing step comprises: 
 heating the substrate.  
 
     
     
         26 . The method of  claim 25  wherein the heating of the substrate occurs in the range of about 400° C. to about 600° C. for a time period of about 30 minutes to about 120 minutes.  
     
     
         27 . The method of  claim 24  further comprising: 
 forming a first pedestal and a second pedestal in the substrate prior to the forming step, wherein a cavity separates the first pedestal from the second pedestal, wherein the exposed portion of the gate oxide includes the first pedestal and excludes the second pedestal.  
 
     
     
         28 . The method of  claim 27  wherein the cavity is filled with oxide.  
     
     
         29 . The method of  claim 24  wherein the step of introducing oxygen ions comprises: 
 implanting oxygen ions into the exposed portion of the gate oxide layer.  
 
     
     
         30 . The method of  claim 29  wherein the implanting step is performed using oxygen plasma in a magnetic field.  
     
     
         31 . The method of  claim 24  further comprising removing the photoresist layer after the introducing step.  
     
     
         32 . The method of  claim 24  wherein the substrate is a silicon substrate.  
     
     
         33 . The method of  claim 24  wherein the oxygen ions of the introducing step are implanted resulting in a peak range of implanted ions of about 20 Angstroms to about 50 Angstroms with a range straggle of about 10 Angstroms to about 25 Angstroms.  
     
     
         34 . A method for forming a dual gate oxide comprising: 
 forming a first gate region and a second gate region;    depositing an oxide layer over the first gate region and the second gate region;    masking the first gate region, wherein a surface of the second gate region remains exposed to form an exposed surface;    implanting oxygen ions into the exposed surface; and,    oxidizing the substrate, wherein a thickness of the oxide layer over the first gate region is thinner than a thickness of the oxide layer over the second gate region.    
     
     
         35 . The method of  claim 34  wherein the masking step comprises: 
 depositing a photoresist layer over the gate oxide layer; and,  
 developing away the photoresist layer over the surface of the first gate region, wherein the surface of the first gate region remains exposed to form an exposed surface.  
 
     
     
         36 . The method of  claim 35  wherein the oxidizing step comprises: 
 heating the substrate such that the substrate is oxidized.  
 
     
     
         37 . The method of  claim 36  wherein the heating of the substrate occurs in the range of about 400° C. to about 600° C. for a time period of about 30 minutes to about 120 minutes.  
     
     
         38 . The method of  claim 34  wherein the substrate is a silicon substrate.  
     
     
         39 . The method of  claim 34  wherein the oxide layer deposited over the first gate region and the second gate region is a nitrided gate oxide.  
     
     
         40 . The method of  claim 34  wherein the ion implantation is accomplished using oxygen plasma in a magnetic field.  
     
     
         41 . The method of claim  40  wherein the magnetic field is generally in the range of about 1 gauss to about 100 gauss.