Method of coating a surface of a substrate with a metal by electroplating

Abstract

The object of the present invention is a method of coating a surface of a substrate with copper by electroplating. According to the invention, this method comprises: a step during which the said surface to be coated is brought into contact with an electroplating bath while the said surface is not under electrical bias; a step of forming the coating during which the said surface is biased; a step during which the said surface is separated from the electroplating bath while it is under electrical bias; the aforementioned electroplating bath comprising, in solution in a solvent: a source of copper ions, with a concentration of between 0.4 and 40 mM; and at least one copper complexing agent.

1 . Method of coating a surface of a substrate with copper by electroplating, characterized in that it comprises: 
 a step referred to as “cold entry” during which the said surface to be coated is brought into contact with an electroplating bath while the said surface is not under electrical bias;    a step of forming the coating during which the said surface is biased for a time long enough to form the said coating;    a step referred to as “hot exit” during which the said surface is separated from the electroplating bath under electrical bias; and in that the aforementioned electroplating bath comprises, in solution in a solvent:    a source of copper ions, with a concentration of between 0.4 and 40 mM; and    at least one copper complexing agent chosen from the group comprising primary aliphatic amines, secondary aliphatic amines, tertiary aliphatic amines, aromatic amines, nitrogen heterocycles, and oximes.    
   
   
       2 . Method according to  claim 1 , wherein, during the aforementioned “cold” entry step, the surface to be coated is kept in contact with the electroplating bath for a period of at least 5 seconds.  
   
   
       3 . Method according to  claim 1  wherein the aforementioned step of forming the coating is carried out by biasing in galvanostatic mode, preferably within the current range from 0.1 mA/cm 2  (milliamps per square centimetre) to 5 mA/cm 2 , and more particularly from 0.1 mA/cm 2  to 1 mA/cm 2 .  
   
   
       4 . Method according to  claim 1  wherein the aforementioned step of forming the coating is carried out by biasing in potentiostatic mode, preferably imposing a cell voltage so that the resulting cell current lies within the 0.1 mA/cm 2  to 5 mA/cm 2  range, and more particularly the 0.1 mA/cm 2  to 1 mA/cm 2  range.  
   
   
       5 . Method according to  claim 1  wherein the aforementioned step of forming the coating is carried out by biasing in pulsed mode, preferably so as to impose voltage pulses corresponding to a maximum cathode current per unit area within the range from 0.1 mA/cm 2  to 5 mA/cm 2 , and more particularly from 0.1 mA/cm 2  to 1 mA/cm 2 , and to a minimum cathode current per unit area within the range from 0 mA/cm 2  to 0.5 mA/cm 2 , and more particularly from 0 mA/cm 2  to 0.1 mA/cm 2 .  
   
   
       6 . Method according to  claim 1 , wherein, during the “cold entry” step, the surface to be coated is maintained in contact with the electroplating bath for a period of between 10 and 60 seconds, preferably for a period of about 10 to 30 seconds.  
   
   
       7 . Method according to  claim 1 , wherein the aforementioned substrate is a silicon wafer in the course of fabricating integrated circuits, the surface of which, to be coated, is that of a copper diffusion barrier layer, such as a bilayer based on tantalum nitride/tantalum (TaN/Ta) or just a tantalum nitride (TaN) layer.  
   
   
       8 . Method according  claim 1 , wherein, during the “hot exit” step, the coated surface is withdrawn from the electroplating bath while under bias for a period of between 1 and 10 seconds, preferably for a period of about 1 to 5 seconds.  
   
   
       9 . Method according to  claim 1 , wherein, in the aforementioned electroplating bath: 
 the copper/complexing agent(s) molar ratio is between 0.1 and 2.5, preferably between 0.3 and 1.3; and    the pH of the said composition is less than 7, preferably between 3.5 and 6.5.    
   
   
       10 . Method according to  claim 1 , wherein, in the aforementioned electroplating bath, the aforementioned solvent is chosen from water and hydroalcoholic mixtures and the source of copper ions is a copper salt, such as in particular copper sulphate, copper chlorate, copper nitrate or copper acetate, preferably copper sulphate.  
   
   
       11 . Method according to  claim 1 , wherein, in the aforementioned electroplating bath, the aforementioned copper complexing agent is a nitrogen heterocycle chosen from pyridine, 2,2′-bipyridine, 8-hydroxyquinoline sulphonate, 1,10-phenanthroline, 3,5-dimethylpyridine and 2,2′-bipyrimidine.  
   
   
       12 . Method according to the aforementioned electroplating bath includes a mixture of pyridine and 2,2′-bipyridine as copper complexing agents.  
   
   
       13 . Method according to one  claim 1 , wherein the aforementioned electroplating bath comprises, in aqueous solution: 
 copper sulphate, with a concentration of between 0.4 and 40 mM;    a mixture of pyridine and 2,2′-bipyridine as copper complexing agents;    the copper/complexing agents molar ratio being between 0.2 and 0.6; and    the pH of the said composition being less than 7, preferably between 3.5 and 6.5. one copper complexing agent.