Novel low leakage current cascaded diode structure

Abstract

A cascaded diode acting as all ESD protection device with reduced substrate leakage current is disclosed. The cascaded diode is composed of a chain of coupled similar elemental diodes, each composed of an n-well in a p-substrate, the n-well having p regions and n regions, and a deep n-well disposed under and connected to the n-well. The first elemental diode has its p region electrically connected to a pin or pad that is the higher potential end of a portion of an integrated circuit to be protected, its n region electrically connected to the p region of an intermediate elemental diode. The p region of an intermediate diode is connected electrically to the n region of the preceding elemental diode and the n region of an intermediate elemental diode is connected electrically to the p region of the following elemental diode. A last elemental diode has its p region electrically connected to the n region of the preceding elemental diode and its n region electrically connected to a pad or pin that is the end of the portion of an integrated circuit.

What is claimed is:  
     
         1 . A cascaded diode acting as an ESD protection device with reduced substrate leakage current, comprising: 
 a chain of coupled similar elemental diodes, each composed of an n-well in a p-substrate, the n-well having p regions and n regions, and a deep n-well disposed under and connected to the n-well;    a first elemental diode having its said p region electrically connected to a pin or pad that is the higher potential end of a portion of an integrated circuit to be protected, its said n region electrically connected to the p region of an intermediate elemental diode, said p region of an intermediate diode connected electrically to the n region of the preceding elemental diode and said n region of an intermediate elemental diode connected electrically to the p region of the following elemental diode, and a last elemental diode having its said p region electrically connected to the n region of the preceding elemental diode and its said n region electrically connected to a pad or pin that is the end of said portion of an integrated circuit.    
     
     
         2 . The cascaded diode of  claim 1  wherein the number of elemental diodes is between 1 and 10.  
     
     
         3 . The cascaded diode of  claim 1  wherein the doping concentration of the n-well is between 5E16 and 1E18 per cc.  
     
     
         4 . The cascaded diode of  claim 1  wherein the depth of said n-well is between 1.5 and 2 micrometers.  
     
     
         5 . The cascaded diode of  claim 1  wherein the doping concentration of the deep n-well is between 1E17 and 5E18 per cc.  
     
     
         6 . The cascaded diode of  claim 1  wherein the depth of said deep n-well is between 2.5 and 4 micrometers.  
     
     
         7 . A method for forming a cascaded diode providing ESD protection to portions of integrated circuits with reduced substrate leakage current, said cascaded diode being a chain of coupled elemental diodes, comprising: 
 fabricating elemental diodes by forming for each diode, an n-well in a p-substrate, a p region and an n region in the n-well, and forming a deep n-well disposed tinder and connected to the n-well;    connecting electrically the p region of a first elemental diode to a pin or pad at the higher potential side of said portion of an integrated circuit to be protected and the n region of said first elemental region to the p region of the following intermediate elemental diode;    connecting electrically the p region of an intermediate diode to the n region of the preceding elemental diode and said n region of an intermediate elemental diode to the p region of the following elemental diode;    connecting electrically the p region a last elemental diode to the n region of the preceding elemental diode and its said n region to the other end of said portion of an integrated circuit.    
     
     
         8 . The method of  claim 7  wherein the number of elemental diodes is between 1 and 10.  
     
     
         9 . The method of  claim 7  wherein the n-well is formed by the implantation of phosphorous ions.  
     
     
         10 . The method of  claim 7  wherein the deep n-well is formed either by a single or by a double implantation of phosphorous ions.  
     
     
         11 . A cascaded diode acting as a Vdd-to-Vss clamp with reduced substrate leakage current and providing ESD protection, comprising: 
 a chain of coupled similar elemental diodes, each composed of an n-well in a p-substrate, the n-well having p regions and n regions, and a deep n-well disposed under and connected to the n-well;    a first elemental diode having its said p region electrically connected to Vdd, its said n region electrically connected to the p region of an intermediate elemental diode, said p region of an intermediate diode connected electrically to the n region of the preceding elemental diode and said n region of an intermediate elemental diode connected electrically to the p region of the following elemental diode, and a last elemental diode having its said p region electrically connected to the n region of the preceding elemental diode and its said n region electrically connected to Vss.    
     
     
         12 . The cascaded diode of  claim 11  wherein the number of elemental diodes is between 1 and 10.  
     
     
         13 . The cascaded diode of  claim 11  wherein the doping concentration of the n-well is between 5E16 and 1E18 per cc.  
     
     
         14 . The cascaded diode of  claim 11  wherein the depth of said n-well is between 1.5 and 2 micrometers.  
     
     
         15 . The cascaded diode of  claim 11  wherein the doping concentration of the deep n-well is between 1E17 and 5E18 per cc.  
     
     
         16 . The cascaded diode of  claim 11  wherein the depth of said deep n-well is between 2.5 and 4 micrometers.  
     
     
         17 . A method for forming a cascaded diode acting as a Vdd-to-Vss clamp with reduced substrate leakage current and providing ESD protection, said cascaded diode being a chain of coupled elemental diodes, comprising: 
 fabricating elemental diodes by forming for each diode, an n-well in a p-substrate, a p region and an n region in the n-well, and forming a deep n-well disposed under and connected to the n-well;    connecting electrically the p region of a first elemental diode to Vdd, the n region of said first elemental region to the p region of the following intermediate elemental diode;    connecting electrically the p region of an intermediate diode to the n region of the preceding elemental diode and said n region of an intermediate elemental diode to the p region of the following elemental diode;    connecting electrically the p region a last elemental diode to the n region of the preceding elemental diode and its said n region to Vss.    
     
     
         18 . The method of  claim 17  wherein the number of elemental diodes is between 1 and 10.  
     
     
         19 . The method of  claim 17  wherein the n-well is formed by the implantation of phosphorous ions.  
     
     
         20 . The method of  claim 17  wherein the deep n-well is formed by either a single or by a double implantation of phosphorous ions.  
     
     
         21 . A cascaded diode acting as a coupling clamp, Vdd-to-Vddo or Vss-to-Vsso, with reduced substrate leakage current and providing ESD protection, comprising: 
 a chain of coupled similar elemental diodes, each composed of an n-well in a p-substrate, the n-well having p regions and Ii regions, and a deep n-well disposed under and connected to the n-well;    a first elemental diode having its said p region electrically connected to Vddo, for Vdd-to-Vddo, or Lasso, for Vss-to-Vsso, its said n region electrically connected to the p region of the following elemental diode, said p region of an intermediate diode connected electrically to the n region of the preceding elemental diode and said n region of an intermediate elemental diode connected electrically to the p region of the following elemental diode, and a last elemental diode having its said p region electrically connected to the n region of the preceding elemental diode and its said n region electrically connected to Vdd, for Vdd-to-Vddo, or Vss, for Vss-to-Vss.    
     
     
         22 . The cascaded diode of  claim 21  wherein the number of elemental diodes is between 1 and 10.  
     
     
         23 . The cascaded diode of  claim 21  wherein the doping concentration of the N-well is between 5E16 and 1E18 per cc.  
     
     
         24 . The cascaded diode of  claim 21  wherein the depth of said n-well is between 1.5 and 2 micrometers.  
     
     
         25 . The cascaded diode of  claim 21  wherein the doping concentration of the deep n-well is between 1E17 and 5ES18 per cc.  
     
     
         26 . The cascaded diode of  claim 21  wherein the depth of said deep n-well is between 2.5 and 4 micrometers.  
     
     
         27 . A method for forming a cascaded diode acting as a coupling clamp, Vdd-to-Vddo or Vss-to-Vsso, with reduced substrate leakage current and providing ESD protection, said cascaded diode being a chain of coupled elemental diodes, comprising: 
 fabricating elemental diodes by forming for each diode, an n-well in a p-substrate, a p region and an n region in the n-well, and forming a deep n-well disposed under and connected to the n-well;    connecting electrically the p region of a first elemental diode to Vddo, for Vdd-to-Vddo, or to Vs so, for Vss-to-Vsso, and the n region of said first elemental region to the p region of the following intermediate elemental diode;    connecting electrically the p region of an intermediate diode to the n region of the preceding elemental diode and said n region of an intermediate elemental diode to the p region of the following elemental diode;    connecting electrically the p region a last elemental diode to the n region of the preceding elemental diode and its said n region to Vdd, for Vdd-to-Vddo, or Vss, for Vss-to-Vsso.    
     
     
         28 . The method of  claim 27  wherein the number of elemental diodes is between 1 and 10.  
     
     
         29 . The method of  claim 27  wherein the n-well is formed by the implantation of phosphorous ions.  
     
     
         30 . The method of  claim 27  wherein the deep n-well is formed either by single or by a double implantation of phosphorous ions.  
     
     
         31 . A cascaded diode acting as a high-voltage-tolerant I/O-to-Vdd clamp, with reduced substrate leakage current and providing ESD protection, comprising: 
 a chain of coupled similar elemental diodes, each composed of an n-well in a p-substrate, the n-well having p regions and n regions, and a deep n-well disposed under and connected to the n-well;    a first elemental diode having its said p region electrically connected to a high-voltage-tolerant I/O pad, its said n region electrically connected to the p region of the following elemental diode, said p region of an intermediate diode connected electrically to the n region of the preceding elemental diode and said n region of an intermediate elemental diode connected electrically to the p region of the following elemental diode, and a last elemental diode having its said p region electrically connected to the n region of the preceding elemental diode and its said n region electrically connected to Vdd.    
     
     
         32 . The cascaded diode of  claim 31  wherein the number of elemental diodes is between 1 and 10.  
     
     
         33 . The cascaded diode of  claim 31  wherein the doping concentration of the n-well is between 5E16 and 1E18 per cc.  
     
     
         34 . The cascaded diode of  claim 31  wherein the depth of said n-well is between 1.5 and 2 micrometers.  
     
     
         35 . The cascaded diode of  claim 31  wherein the doping concentration of the deep n-well is between 1E17 and 5E18 per cc.  
     
     
         36 . The cascaded diode of  claim 31  wherein the depth of said deep n-well is between 2.5 and 4 micrometers.  
     
     
         37 . A method for forming a cascaded diode acting as a high-voltage-tolerant I/O-to-Vdd clamp, with reduced substrate leakage current and providing ESD protection, said cascaded diode being a chain of coupled elemental diodes, comprising: 
 fabricating elemental diodes by forming for each diode, an n-well in a p-substrate, a p region and an n region in the n-well, and forming a deep n-well disposed under and connected to the n-well;    connecting electrically the p region of a first elemental diode to a high-voltage-tolerant I/O pad, and the n region of said first elemental region to the p region of the following intermediate elemental diode;    connecting electrically the p region of an intermediate diode to the n region of the preceding elemental diode and said n region of an intermediate elemental diode to the p region of the following elemental diode;    connecting electrically the p region a last elemental diode to the n region of the preceding elemental diode and its said n region to Vdd.    
     
     
         38 . The method of  claim 37  wherein the number of elemental diodes is between 1 and 10.  
     
     
         39 . The method of  claim 37  wherein the n-well is formed by the implantation of phosphorous ions.  
     
     
         40 . The method of  claim 37  wherein the deep n-well is formed either by a single or by a double implantation of phosphorous ions.  
     
     
         41 . A double n-well diode comprising: 
 an n-well in a p-substrate;    p regions and n regions within the n-well;    a deep n-well disposed under and connected to the n-well;    
     
     
         42 . The diode of  claim 41  wherein the doping concentration of the n-well is between 5E16 and 1E15 per cc.  
     
     
         43 . The diode of  claim 41  wherein the depth of said n-well is between 1.5 and 2 micrometers.  
     
     
         44 . The diode of  claim 41  wherein the doping concentration of the deep n-well is between 1E17 and 5E18 per cc.  
     
     
         45 . The diode of  claim 41  wherein the depth of said deep n-well is between 2.5 and 4 micrometers.  
     
     
         46 . A method for forming a diode comprising: 
 forming an n-well in a p-substrate;    forming p regions and n regions in the n-well:    forming a deep n-well disposed under and connected to the n-well.    
     
     
         47 . The method of  claim 46  wherein the n-well is formed by the implantation of phosphorous ions.  
     
     
         48 . The method of  claim 46  wherein the deep n-well is formed either by a single or by a double implantation of phosphorous ions.