Electrolyte and Method for Cobalt Electrodeposition

Abstract

The present invention relates to a method for fabricating cobalt interconnects and an electrolyte enabling it to be implemented. The electrolyte of pH less than 4.0 comprises cobalt ions, chloride ions and organic additives, including an alpha-hydroxy carboxylic acid and an amine chosen from polyethyleneimine or benzotriazole.

1 . Electrolyte for the electrodeposition of cobalt characterized in that the electrolyte is an aqueous solution comprising from 1 to 5 g/L of cobalt II ions, from 1 to 10 g/L of chloride ions, a strong acid in a sufficient quantity to obtain a pH comprised between 1.8 and 4.0, and organic additives including at least one first additive chosen from alpha-hydroxy carboxylic acids and mixtures thereof and at least one second additive chosen from polyethyleneimines and benzotriazole. 
     
     
         2 . Electrolyte according to  claim 1 , characterized in that the total concentration of organic additives in the electrolyte is comprised between 5 ppm and 50 ppm. 
     
     
         3 . Electrolyte according to  claim 1 , characterized in that the concentration of the second additive is comprised between 1 ppm and 10 ppm. 
     
     
         4 . Electrolyte according to  claim 1 , characterized in that it does not contain any sulphur compound. 
     
     
         5 . Electrolyte according to  claim 1 , characterized in that its pH is comprised between 1.8 and 2.6. 
     
     
         6 . Electrolyte according to  claim 5 , characterized in that the first additive is chosen from citric acid, tartaric acid, malic acid, mandelic acid and glyceric acid. 
     
     
         7 . Electrolyte according to  claim 1 , characterized in that its conductivity is comprised between 2 mS/cm and 10 mS/cm. 
     
     
         8 . Electrolyte according to  claim 5 , characterized in that it does not contain boric acid. 
     
     
         9 . Electrochemical method for deposition on a substrate provided with a conductive surface comprising a flat part and cavities, by filling said cavities bottom-up, said method comprising:
 a step of contacting the conductive surface with an electrolyte according to  claim 1 ,   an electrical step of polarizing the conductive surface for a sufficient duration to perform a cobalt deposition on the surface.   
     
     
         10 . Electrochemical method for depositing cobalt according to  claim 9 , characterized in that the duration is sufficient to perform the filling of the cavities and the coating of the flat part by a cobalt deposit having a thickness ranging from 50 nm to 400 nm. 
     
     
         11 . Electrochemical method for depositing cobalt according to  claim 9 , characterized in that the polarization step is immediately followed by a polishing step combining chemical and mechanical attack of the cobalt deposit obtained at the end of the polarization step. 
     
     
         12 . Method according to  claim 9 , wherein the cavities have a width at their opening of less than 100 nm, preferably comprised between 10 and 50 nm and a depth comprised between 50 nm and 250 nm. 
     
     
         13 . Method according to  claim 9 , wherein the cobalt deposit obtained at the end of the polarization step has an impurity content less than 1000 atomic ppm. 
     
     
         14 . Method according to  claim 9 , wherein the cobalt deposit obtained at the end of the electrodeposition step comprises a mean void percentage of less than 10% by volume or by area, without undergoing a heat treatment at a temperature ranging from 50° C. to 500° C. 
     
     
         15 . Method according to  claim 9 , wherein the cobalt deposition rate is comprised between 0.1 nm/s and 3.0 nm/s when the intensity of the polarization current ranges from 8.5 mA/cm 2  to 18.5 mA/cm 2 . 
     
     
         16 . Method according to  claim 9 , wherein the resistivity of the cobalt deposit obtained at the end of the polarization step is less than 30 μ∩·cm without undergoing a heat treatment at a temperature ranging from 50° C. to 500° C. 
     
     
         17 . Method according to  claim 9 , wherein the substrate is obtained by successive deposits of SiO 2 , tantalum nitride and cobalt. 
     
     
         18 . Method according to  claim 17 , characterized in that the cobalt is deposited on tantalum nitride by chemical vapor deposition (CVD) or by atomic layer deposition (ALD).