Electroless plating with a floating potential

Abstract

Exemplary methods of plating are described. The methods may include applying a floating potential to a plating bath in a plating chamber. The methods further include contacting a patterned substrate with the plating bath in the plating chamber. The patterned substrate includes at least one metal interconnect with a contact surface that is exposed to the plating bath. The metal interconnect is made of a first metal characterized by a first reduction potential. The methods further include plating a diffusion layer on the contact surface of the metal interconnect. The diffusion layer is made of a second metal characterized by a second reduction potential that is larger than the first reduction potential of the first metal in the metal interconnects. The plating bath also includes one or more ions of the second metal and a grain refining compound that reduces the formation of pinhole defects in the diffusion layer.

What is claimed is: 
     
         1 . A plating method comprising:
 applying a floating potential to a plating bath in a plating chamber;   contacting a patterned substrate with the plating bath in the plating chamber, wherein the patterned substrate comprises at least one metal interconnect with a contact surface that is exposed to the plating bath, and wherein the metal interconnect is made of a first metal characterized by a first reduction potential; and   plating a diffusion layer on the contact surface of the metal interconnect, wherein the diffusion layer is made of a second metal characterized by a second reduction potential that is larger than the first reduction potential of the first metal in the at least one metal interconnect, wherein the plating bath comprises one or more ions of the second metal and a grain refining compound that reduces the formation of pinhole defects in the diffusion layer.   
     
     
         2 . The plating method of  claim 1 , wherein the first metal in the at least one metal interconnect is copper. 
     
     
         3 . The plating method of  claim 1 , wherein the second metal in the diffusion layer is selected from the group consisting of silver, gold, platinum, palladium, and germanium. 
     
     
         4 . The plating method of  claim 1 , wherein the grain refining compound comprises glyoxylic acid or ethylene diamine tetraacetic acid. 
     
     
         5 . The plating method of  claim 1 , wherein the grain refining compound is characterized by a concentration in the plating bath of less than or about 0.05 M. 
     
     
         6 . The plating method of  claim 1 , wherein the plating bath further comprises at least one stabilizer compound comprising imidazole or succinimide. 
     
     
         7 . The plating method of  claim 1 , wherein the diffusion layer is plated on the contact surface of the metal interconnect by electroless plating. 
     
     
         8 . The plating method of  claim 1 , wherein the plating bath is characterized by a temperature of less than or about 25° C. during the plating of the diffusion layer. 
     
     
         9 . A plating method comprising:
 applying a floating potential to a plating bath in a plating chamber;   contacting a patterned substrate with the plating bath in the plating chamber, the patterned substrate comprises at least one copper interconnect with a contact surface that is exposed to the plating bath; and   plating a diffusion layer on the contact surface of the copper interconnect, wherein the diffusion layer is made of silver, wherein the plating bath is characterized by a temperature of less than or about 25° C. during the plating of the diffusion layer.   
     
     
         10 . The plating method of  claim 9 , wherein the plating bath is characterized by a concentration of silver ions that is less than or about 0.01 M. 
     
     
         11 . The plating method of  claim 9 , wherein the diffusion layer is plated on the contact surface of the copper interconnect at a rate of less than or about 1 nm/min. 
     
     
         12 . The plating method of  claim 9 , wherein the diffusion layer is characterized by a thickness of less than or about 10 nm, and wherein the diffusion layer is free of pinhole defects. 
     
     
         13 . The plating method of  claim 9 , wherein the plating bath further comprises a grain refining compound selected from the group consisting of glyoxylic acid and ethylene diamine tetraacetic acid. 
     
     
         14 . The plating method of  claim 9 , wherein the plating bath further comprises at least one stabilizer compound comprising imidazole or succinimide. 
     
     
         15 . A plating method comprising:
 applying a floating potential to a plating bath in a plating chamber;   contacting a patterned substrate with the plating bath in the plating chamber, the patterned substrate comprises at least one copper interconnect with a contact surface that is exposed to the plating bath; and   plating a diffusion layer on the contact surface of the copper interconnect, wherein the diffusion layer is made of silver.   
     
     
         16 . The plating method of  claim 15 , wherein the floating potential is characterized by a voltage of greater than or about −10 V. 
     
     
         17 . The plating method of  claim 15 , wherein the diffusion layer is characterized by less than or about 5 pinhole defects per bond pad. 
     
     
         18 . The plating method of  claim 15 , wherein a thickness of the diffusion layer of greater than or about 1 nm is plated on the contact surface of the copper interconnect in less than or about 30 seconds. 
     
     
         19 . The plating method of  claim 15 , wherein the diffusion layer is plated on the contact surface of the copper interconnect by electroless plating. 
     
     
         20 . The plating method of  claim 15 , wherein the patterned substrate comprises silicon.