Method to eliminate arsenic contamination in trench capacitors

Abstract

A trench capacitor structure in which arsenic contamination is substantially reduced and/or essentially eliminated from diffusing into a semiconductor substrate along sidewalls of a trench opening having a high aspect ratio is provided. The present invention also provides a method of fabricating such a trench capacitor structure as well as a method for detecting the arsenic contamination during the drive-in annealing step. The detection of arsenic for product running through the manufacturing lines uses the effect of arsenic enhanced oxidation. That is, the high temperature oxidation anneal used to drive arsenic into the semiconductor substrate is monitored for thickness. For large levels of arsenic outdiffusion, the oxidation rate will increase resulting in a thicker oxide layer. If such an event is detected, the product that has been through the process steps to form the buried plate up to the drive-in anneal, can be reworked to reduce arsenic contamination.

1 . A method of fabricating a semiconductor structure comprising: 
 providing a semiconductor substrate having at least one trench opening having an aspect ratio of greater than 3.0 located therein, said at least one trench opening having sidewalls that extend to a common bottom wall;    providing a recessed arsenic-containing film within a bottom portion of said at least one trench opening, while maintaining the sidewalls in an upper portion of the at least one trench opening essentially free of residual arsenic; and    annealing in an oxygen-containing ambient to cause outdiffusion of arsenic from said recessed arsenic-containing film into said semiconductor substrate, wherein during said annealing oxide growth within the at least one trench opening is monitored.    
   
   
       2 . The method of  claim 1  wherein said providing said semiconductor substrate having said at least one trench opening comprises lithography and etching.  
   
   
       3 . The method of  claim 1  wherein said providing said recessed arsenic-containing film comprises forming an arsenic-containing film within the at least one trench opening covering said sidewalls and said bottom wall, forming a first photoresist within said at least one trench opening on said arsenic-containing film, recessing said first photoresist to expose portions of the arsenic-containing film in the upper portion of the at least one trench opening, and entirely removing said arsenic-containing film from said upper portion of said at least one trench opening.  
   
   
       4 . The method of  claim 3  wherein said entirely removing said arsenic-containing film comprises recessing said arsenic-containing film from said upper portion whereby a residual arsenic-containing film remains, forming a first dielectric cap within said at least one trench opening and stripping said first dielectric cap and said residual arsenic-containing film from said at least one trench opening.  
   
   
       5 . The method of  claim 1  wherein said annealing is performed at a temperature of 800° C. or above.  
   
   
       6 . The method of  claim 1  wherein said oxygen-containing ambient comprises one of O 2 , NO or ozone.  
   
   
       7 . The method of  claim 1  wherein said monitoring includes an oxide thickness monitor.  
   
   
       8 . The method of  claim 1  further comprising forming a trench dielectric, a conductive material and a collar region within said at least one trench opening, wherein said trench dielectric is located between said conductive material and said outdiffused arsenic.  
   
   
       9 . The method of  claim 1  wherein said undiffused arsenic forms a buried plate of a trench capacitor that has an outdiffused thickness of about 100 nm or less.  
   
   
       10 . The method of  claim 4  wherein said outdiffused arsenic forms a buried plate of a trench capacitor that has an arsenic concentration of less than about 9×10 18  atoms/cm 3 .