Method for obtaining extreme selectivity of metal nitrides and metal oxides

Abstract

Methods for etching metal nitrides and metal oxides include using ultradilute HF solutions and buffered, low-pH HF solutions containing a minimal amount of the hydrofluoric acid species H 2 F 2 . The etchant can be used to selectively remove metal nitride layers relative to doped or undoped oxides, tungsten, polysilicon, and titanium nitride. A method is provided for producing an isolated capacitor, which can be used in a dynamic random access memory cell array, on a substrate using sacrificial layers selectively removed to expose outer surfaces of the bottom electrode.

We claim: 
     
         1 . A method of selectively etching a layer of metal nitrides or metal oxide, the method comprising:
 heating a substrate having formed thereon a structure comprising a layer of metal oxide or metal nitride;   exposing the structure to a buffered hydrofluoric acid etch solution having a pH between about 3.5 and about 5.5; and   selectively etching the layer of metal oxide or metal nitride with an etch rate selectivity relative to an exposed layer of silicon greater than or equal to about 2000:1.   
     
     
         2 . The method of  claim 1 , wherein heating the substrate comprises heating to a temperature between about 50° C. and about 90° C. 
     
     
         3 . The method of  claim 1 , wherein the etch solution has a pH of between about 4.0 and 5.0. 
     
     
         4 . The method of  claim 1 , wherein the etch solution has a buffer to hydrofluoric ratio that is greater than about 400:1. 
     
     
         5 . The method of  claim 1 , wherein the exposed layer of silicon is a layer of polysilicon and selectively etching comprises etching with an etch rate selectivity relative to the exposed layer of polysilicon that is greater than or equal to about 2000:1. 
     
     
         6 . The method of  claim 1 , wherein the layer of metal oxide or metal nitride comprises a material selected from the group consisting of hafnium oxide, hafnium nitride, aluminum oxide, aluminum nitride and a combination thereof. 
     
     
         7 . A method of selectively removing a sacrificial material, the method comprising:
 providing a structure which includes a sacrificial material comprising a metal oxide or a metal nitride and further includes a nonsacrificial material;   exposing the structure to a buffered hydrofluoric acid solution having a pH between about 3.5 and 5.5 and heated to a temperature between about 50° C. and about 90° C.; and   selectively removing the sacrificial material from the structure with an etch rate selectivity relative to the nonsacrificial material greater than about 500:1.   
     
     
         8 . The method of  claim 7 , wherein the sacrificial material comprises a material selected from the group consisting of hafnium oxide, hafnium nitride, aluminum oxide, aluminum nitride and a combination thereof. 
     
     
         9 . The method of  claim 8 , wherein the nonsacrificial material is selected from the group consisting of an oxide, polysilicon, tungsten, titanium nitride and a combination thereof. 
     
     
         10 . The method of  claim 9 , wherein the nonsacrificial material is an oxide and selectively removing comprises etching with an etch rate selectivity relative to the nonsacrificial material that is greater than about 800:1. 
     
     
         11 . The method of  claim 9 , wherein the nonsacrificial material is polysilicon and selectively removing comprises etching with an etch rate selectivity relative to the nonsacrificial material that is greater than about 2000:1 
     
     
         12 . The method of  claim 7 , wherein the buffered hydrofluoric acid is heated to a temperature between about 60° C. and about 85° C. 
     
     
         13 . The method of  claim 7 , wherein the sacrificial material comprises the metal oxide and selectively removing comprises etching at an etch rate exceeding about 5000 Å/min. 
     
     
         14 . The method of  claim 7 , wherein the buffered hydrofluoric acid solution has a buffer to hydrofluoric acid ratio that is greater than about 400:1. 
     
     
         15 . A method of selectively removing a sacrificial material, the method comprising:
 providing a structure comprising a sacrificial material and a nonsacrificial material, the sacrificial material comprising a metal oxide or a metal nitride;   exposing the structure to a buffered hydrofluoric acid solution having a buffer to hydrofluoric acid ratio exceeding about 400:1; and   selectively removing the sacrificial material from the structure with an etch rate selectivity relative to the nonsacrificial material exceeding about 500:1.   
     
     
         16 . The method of  claim 15 , wherein the buffered hydrofluoric acid solution has a pH between about 3.5 and 5.5. 
     
     
         17 . The method of  claim 15 , wherein the buffer comprises NH 4 F. 
     
     
         18 . The method of  claim 15 , wherein exposing comprises contacting the structure to the buffered hydrofluoric acid solution that is heated to a temperature between about 50° C. and about 90° C. 
     
     
         19 . The method of  claim 15 , wherein the buffered hydrofluoric acid solution has a buffer to hydrofluoric ratio that is greater than about 500:1.