Method for depositing a copper seed layer onto a barrier layer and copper plating bath

Abstract

The present invention relates to an aqueous electroless copper plating bath, including a source for Cu(II) ions, glyoxylic acid as the reducing agent for Cu(II) ions, at least one complexing agent for Cu(II) ions and at least one source for hydroxide ions selected from the group consisting of RbOH, CsOH and mixtures thereof, wherein the electroless copper plating bath is substantially free of Na+, K+ and tetraalkylammonium ions.

1 . An aqueous electroless copper plating bath, comprising
 a. a source for Cu(II) ions,   b. glyoxylic acid as the reducing agent for Cu(II) ions,   c. at least one complexing agent for Cu(II) ions and   d. at least one source for hydroxide ions selected from the group consisting of RbOH, CsOH and mixtures thereof,   wherein said electroless copper plating bath is substantially free of Na + , K +  and tetraalkylammonium ions.   
     
     
         2 . The aqueous electroless copper plating bath of  claim 1  with a pH ranging between 10 and 14. 
     
     
         3 . The aqueous electroless copper plating bath of  claim 1 , wherein the source for Cu(II) ions is selected from copper sulfate, copper chloride, copper nitrate, copper acetate, copper methane sulfonate, copper hydroxide, copper formate and hydrates thereof. 
     
     
         4 . The aqueous electroless copper plating bath of  claim 1 , wherein the Cu(II) ions have a concentration ranging from 0.05 g/l to 20 g/l. 
     
     
         5 . The aqueous electroless copper plating bath of  claim 1 , wherein the glyoxylic acid has a concentration ranging from 0.05 g/l to 20 g/l. 
     
     
         6 . The aqueous electroless copper plating bath of  claim 1 , wherein the glyoxylic acid has a concentration ranging from 0.1 g/l to 10 g/l. 
     
     
         7 . The aqueous electroless copper plating bath of  claim 1 , wherein the glyoxylic acid has a concentration ranging from 0.2 g/l to 6 g/l. 
     
     
         8 . The aqueous electroless copper plating bath of  claim 1 , wherein the at least one complexing agent for Cu(II) ions is selected from the group consisting of carboxylic acids, hydroxycarboxylic acids, aminocarboxylic acids, alkanolamines, polyols and mixtures thereof. 
     
     
         9 . The aqueous electroless copper plating bath of  claim 1 , wherein the at least one complexing agent for Cu(II) ions is selected from the group consisting of hydroxycarboxylic acids, alkanolamines, and mixtures thereof. 
     
     
         10 . The aqueous electroless copper plating bath of  claim 1 , wherein the at least one complexing agent for Cu(II) ions is at least one polyamino disuccinic acid derivative. 
     
     
         11 . The aqueous electroless copper plating bath of  claim 1 , wherein the at least one complexing agent for Cu(II) ions is a combination of i) at least one polyamino disuccinic acid derivative and ii) one or more compounds selected from the group consisting of ethylenediamine tetraacetic acid, N′-(2-Hydroxyethyl)-ethylenediamine-N,N,N′-triacetic acid, and N,N,N′,N′-Tetrakis-(2-hydroxypropyl)-ethylenediamine. 
     
     
         12 . The aqueous electroless copper plating bath of  claim 1 , wherein the at least one complexing agent for Cu(II) ions is a combination of i) i) N,N,N′,N′-tetrakis-(2-hydroxypropyl)ethylenediamine and ii) one or more from ethylenediamine tetraacetic acid and N′-(2-Hydroxyethyl)-ethylenediamine-N,N,N′-triacetic acid. 
     
     
         13 . The aqueous electroless copper plating bath of  claim 1 , wherein the at least one source for hydroxide ions is CsOH. 
     
     
         14 . The aqueous electroless copper plating bath of  claim 1 , comprising a wetting-agent selected from the group comprising cationic wetting agents, anionic wetting agents, non-ionic wetting agents, amphoteric wetting agents and mixtures thereof. 
     
     
         15 . The aqueous electroless copper plating bath of  claim 1 , comprising a wetting agent selected from the group consisting of polyethyleneglycol, polypropyleneglycol, polyethyleneglycol-polypropyleneglycol co-polymers, alcohol alkoxylates, alkoxylated fatty acid and mixtures thereof. 
     
     
         16 . The aqueous electroless copper plating bath of  claim 1 , wherein the concentration of the wetting agent in the aqueous electroless copper plating bath ranges from 0.1 to 100 g/l. 
     
     
         17 . The aqueous electroless copper plating bath of  claim 1 , comprising at least one stabilizing agent. 
     
     
         18 . The aqueous electroless copper plating bath of  claim 17 , wherein the at least one stabilizing agent is selected from the group comprising mercaptobenzothiazole, thiourea, cyanide and/or ferrocyanide, cobaltocyanide salts, polyethyleneglycol derivatives, 2,2′-bipyridyl, methyl butynol, and propionitrile. 
     
     
         19 . The aqueous electroless copper plating bath of  claim 17 , wherein the at least one stabilizing agent has a concentration ranging from 0.1 mg/l to 1000 mg/l.