Water soluble and air stable phosphaadamantanes as stabilizers for electroless metal deposition

Abstract

The present invention relates to the use of water soluble and air stable phosphaadamantanes as stabilizers in electrolytes for electroless metal deposition. An electrolyte, as well as a method for the electroless deposition of metals is disclosed. The plated metal layers can comprise nickel, copper, cobalt, boron, silver, palladium or gold, as well as alloys comprising at least one of the aforementioned metals as an alloying metal. The present invention further relates to an organic stabilizer for electroless plating processes, and an electrolyte for the electroless deposition of a metal layer on a substrate, comprising a metal ion source for the metal to be deposited, a reducing agent, a complexing agent, a stabilizer and preferably an accelerator. A method for the electroless deposition of a metal layer on a surface from an electrolyte according to the invention is also disclosed.

1 . An aqueous electrolyte composition for the electroless deposition of a metal layer on a substrate, comprising:
 a metal ion source of the metal to be deposited;   a reducing agent;   a complexing agent;   an accelerator; and   a stabilizer, characterized in that the stabilizer is a phosphaadamantane according to the general Formula I:   
       
         
           
           
               
               
           
         
       
       wherein the hydrogen atoms on carbon atoms 1 to 6 may independently from each other be substituted by a moiety of the group consisting of F, Cl, Br, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, and an alcohol group having 1 to 6 carbon atoms. 
     
     
         2 . The aqueous electrolyte composition according to  claim 1 , wherein the phosphaadamantane is present in a concentration between ≥0.05 mg/L and ≤100 mg/L. 
     
     
         3 . The aqueous electrolyte composition according to  claim 2 , wherein the phosphaadamantane is present in a concentration between ≥0.1 mg/L and ≤25 mg/L. 
     
     
         4 . The aqueous electrolyte composition according to  claim 3 , wherein the phosphaadamantane is present in a concentration between ≥0.5 mg/L and ≤10 mg/L. 
     
     
         5 . The aqueous electrolyte composition according to  claim 1 , wherein the metal to be deposited is at least one metal selected from the group consisting of nickel, copper, cobalt, boron, silver, and gold. 
     
     
         6 . The aqueous electrolyte composition according to  claim 1 , wherein the accelerator is selected from the group consisting of saccharine, hydantoin, rhodanine, carbamide, carbamide derivates and mixtures thereof. 
     
     
         7 . The aqueous electrolyte composition according to  claim 1 , wherein the electrolyte is essentially free of inorganic stabilizers, lead, bismuth, zinc and/or tin. 
     
     
         8 . The aqueous electrolyte composition according to  claim 1 , wherein the composition is essentially free of cyanides, selenium compounds and sulfur compounds comprising sulfur in an oxidation state between −2 and +5. 
     
     
         9 . The aqueous electrolyte composition according to  claim 1 , further comprising at least one additional carboxylic acid and/or at least one salt of a carboxylic acid. 
     
     
         10 . The aqueous electrolyte composition according to  claim 9 , wherein the carboxylic acid is selected from the group consisting of acrylic acids, aromatic carboxylic acids, fatty acids, aliphatic carboxylic acids, keto acids, dicarboxylic acids, tricarboxylic acids, straight chained carboxylic acids, heterocyclic carboxylic acids, saturated carboxylic acids, unsaturated carboxylic acids, α-hydroxy acids, and mixtures thereof. 
     
     
         11 . The aqueous electrolyte composition according to  claim 1 , wherein the pH-value of the composition is in the range of between pH 4 and pH 7. 
     
     
         12 . The aqueous electrolyte composition according to  claim 1 , wherein the reducing agent is selected from the group consisting of sodium hypophosphite, formaldehyde, dimethyl aminoborane, amino borane, other organic boranes, and mixtures thereof. 
     
     
         13 . The aqueous electrolyte composition according to  claim 1 , wherein the complexing agent is selected from the group consisting of 2-hydroxy propionic acid, propanedioic acid (malonic acid), EDTA and amino acetic acid. 
     
     
         14 . A method for the electroless deposition of a metal layer on a substrate comprising the steps of:
 contacting the substrate to be plated with an electrolyte comprising:
 a metal ion source of the metal to be deposited; 
 a reducing agent; 
 a complexing agent; 
 an accelerator; and 
 a stabilizer, characterized in that the electrolyte comprises phosphaadamantane, as a stabilizer, according to the general Formula I: 
   
       
         
           
           
               
               
           
         
         
           wherein the hydrogen atoms on carbon atoms 1 to 6 may independently from each other be substituted by a moiety of the group consisting of F, Cl, Br, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, and an alcohol group having 1 to 6 carbon atoms. 
         
       
     
     
         15 . The method according to  claim 14 , wherein the substrate is contacted with the electrolyte at a temperature within the range of between ≥20° C. and ≤85° C. 
     
     
         16 . The method according to  claim 15 , wherein the substrate is contacted with the electrolyte at a temperature within the range of between ≥25° C. and ≤70° C. 
     
     
         17 . The method according to  claim 14 , wherein the substrate is contacted with the electrolyte for a time between ≥1 s and ≤180 min. 
     
     
         18 . The method according to  claim 17 , wherein the substrate is contacted with the electrolyte for a time preferably between ≥10 s and ≤60 min. 
     
     
         19 . The method according to  claim 14 , wherein the stabilizer in the electrolyte composition is 1,3,5-triaza-7-phosphatricyclo[3,3,1,1]decane (PTA).