Process for manufacturing integrated resistor and phase-change memory element including this resistor

Abstract

A vertical-current-flow resistive element includes a monolithic region having a first portion and a second portion arranged on top of one another and formed from a single material. The first portion has a first resistivity, and the second portion has a second resistivity, lower than the first resistivity. To this aim, a monolithic region with a uniform resistivity and a height greater than at least one of the other dimensions is first formed; then the resistivity of the first portion is increased by introducing, from the top, species that form a prevalently covalent bond with the conductive material of the monolithic region, so that the concentration of said species becomes higher in the first portion than in the second portion. Preferably, the conductive material is a binary or ternary alloy, chosen from among TiAl, TiSi, TiSi 2 , Ta, WSi, and the increase in resistivity is obtained by nitridation.

1 . A method of making a vertical-current-flow resistive element, comprising: 
 forming a monolithic region of a single material having a height greater than at least one other dimension, the forming including:    forming first and second portions of the monolithic region arranged on top of one another, by forming said first portion with a first resistivity and said second portion with a second resistivity lower than said first resistivity.    
     
     
         2 . The method according to  claim 1 , wherein forming said first portion includes adding to the monolithic region a first concentration of species forming a prevalently covalent bond with said single material, and forming said second portion includes adding to the monolithic region a second concentration of said species, lower than said first concentration, wherein said single material is conductive.  
     
     
         3 . The method according to  claim 2 , wherein said species have a decreasing concentration starting from said first portion towards said second portion.  
     
     
         4 . The method according to  claim 2 , wherein said single material is a binary or ternary alloy.  
     
     
         5 . The method according to  claim 4 , wherein said conductive material is chosen from among TiAl, TiSi, TiSi 2 , Ta, and WSi.  
     
     
         6 . The method according to  claim 2 , wherein said species comprise nitrogen.  
     
     
         7 . The method according to  claim 1 , wherein said first portion has an approximately constant resistivity.  
     
     
         8 . The method according to  claim 1 , wherein said second portion has a gradually decreasing resistivity starting from said first portion.  
     
     
         9 . The method according to  claim 1 , further comprising: 
 forming a top electrode of conductive material in electrical contact with said first portion; and    forming a bottom electrode of conductive material in direct electrical contact with said second portion.    
     
     
         10 . The method according to  claim 1 , wherein said monolithic region has a shape chosen from among a column shape, having a height, a width and a depth, wherein the height is greater than the width and the depth; a wall shape, having a height, a width and a depth, wherein the depth and the height are greater than the width: and a closed shape having a height, a width and a perimeter, wherein the height and the perimeter are greater than the width.  
     
     
         11 . A process for manufacturing a vertical-current-flow resistive element, comprising: 
 forming a monolithic region of conductive material having a uniform resistivity and having a first portion and a second portion arranged on top of one another; and    increasing the resistivity of said first portion so that said first portion has a greater resistivity than said second portion.    
     
     
         12 . The process according to  claim 11 , wherein said step of increasing the resistivity comprises enriching said first portion with species that form a prevalently covalent bond with said conductive material.  
     
     
         13 . The process according to  claim 12 , wherein said step of enriching comprises implanting or introducing said species from plasma.  
     
     
         14 . The process according to  claim 12 , wherein said species comprise nitrogen.  
     
     
         15 . The process according to  claim 11 , wherein said conductive material is a binary or ternary alloy.  
     
     
         16 . The process according to  claim 11 , wherein said conductive material is chosen from among TiAl, TiSi, TiSi 2 , Ta, and WSi.  
     
     
         17 . The process according to  claim 11 , further comprising the steps of forming a bottom electrode of conductive material in direct electrical contact with said second portion and forming a top electrode of conductive material in electrical contact with said first portion.  
     
     
         18 . A method of making a phase-change memory element, comprising: 
 forming a programmable element of chalcogenic material; and    forming a resistive element having a first end in direct electrical contact with said programmable element, the resistive element including a monolithic region having a first portion and a second portion arranged on top of one another, the first portion having a first resistivity and said second portion having a second resistivity lower than said first resistivity.    
     
     
         19 . The method of  claim 18 , wherein forming the resistive element includes forming the monolithic region of a conductive material; forming the first portion by adding to the monolithic region a first concentration of a species covalently bonded with the conductive material; and forming the second portion by adding to the monolithic region a second concentration of the species covalently bonded with the conductive material, the first concentration being greater than the second concentration.  
     
     
         20 . The method of  claim 19 , wherein the conductive material is chosen from among TiAl, TiSi, TiSi 2 , Ta, and WSi and the species include nitrogen.  
     
     
         21 . The method of  claim 18  wherein the step of forming the resistive element includes: 
 forming the monolithic region of conductive material having a uniform resistivity; and    increasing the resistivity of the first portion so that the first portion has a greater resistivity than the second portion.    
     
     
         22 . The method of  claim 18 , further comprising: 
 forming a conductive electrode;    forming an insulating layer on the electrode; and    forming an opening that extends through the insulating layer and exposes a portion of the electrode, wherein forming the resistive element includes forming the monolithic region in the opening and in contact with the electrode.    
     
     
         23 . The method of  claim 22  wherein forming the resistive element includes depositing a conductive material in the opening, removing an excess portion of the conductive material from a surface of the insulating layer, and nitridating the conductive material in the opening without using a mask.