Bottom-up fill in damascene features

Abstract

The embodiments herein relate to methods and apparatus for filling features with copper by a bottom-up fill mechanism without the use of organic plating additives. In some cases, filling occurs directly on a semi-noble metal layer, without the deposition of a copper seed layer. In other cases, the filling occurs on a copper seed layer. Factors such as the polarization of electrolyte, the use of a complexing agent, electrolyte pH, electrolyte temperature, and the waveform used to deposit material may contribute to promoting the bottom-up fill.

What is claimed is: 
     
         1 . A method of performing a one step electrofill process to fill features on a partially fabricated integrated circuit, comprising:
 (a) receiving a substrate having an exposed semi-noble metal layer and a plurality of features thereon;   (b) contacting the substrate with electrolyte comprising:
 (i) between about 1-100 mM copper cations; and 
 (ii) a complexing agent that forms a complex with the copper cations, wherein the electrolyte is substantially free of suppressors, accelerators and levelers; and 
   (c) while contacting the electrolyte, electroplating copper into the features by a bottom-up fill mechanism at a substrate potential for electrodeposition between about 0.03 and 0.33 V versus an NHE reference electrode.   
     
     
         2 . The method of  claim 1 , wherein no suppressor, accelerator, or leveler substantially contributes to the bottom-up fill mechanism. 
     
     
         3 . The method of  claim 1 , wherein the bottom-up fill is conducted directly on the semi-noble metal layer, without first forming a seed layer. 
     
     
         4 . The method of  claim 1 , wherein electroplating copper in operation (c) comprises applying a modulated waveform that alternately pulses current at a first level that deposits copper on the substrate and a second level that etches copper from copper that was previously electroplated on the substrate. 
     
     
         5 . The method of  claim 4 , wherein the second level of current that etches copper has an absolute value between about 0.05-0.3 mA/cm 2 , and wherein the pulses of current alternate between the first current level and second current level with a frequency between about 100-1000 Hz. 
     
     
         6 . The method of  claim 1 , wherein the complexing agent is selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), citric acid, and glutamic acid. 
     
     
         7 . The method of  claim 6 , wherein the complexing agent is ethylenediaminetetraacetic acid (EDTA). 
     
     
         8 . The method of  claim 1 , wherein, during electroplating, the electrolyte is held at a temperature between about 20-80° C. 
     
     
         9 . The method of  claim 8 , wherein, during electroplating, the electrolyte is held at a temperature between about 50-70° C. 
     
     
         10 . The method of  claim 1 , wherein, during electroplating, the electroplating surface of the substrate experiences a current density of between about 0.1 and 2 mA/cm 2 . 
     
     
         11 . The method of  claim 1 , wherein a pH of the electrolyte is between about 1-5. 
     
     
         12 . The method of  claim 1 , wherein the semi-noble metal layer comprises a material selected from the group consisting of ruthenium, tungsten, cobalt, osmium, platinum, palladium, aluminum, gold, silver, iridium and rhodium. 
     
     
         13 . The method of  claim 12 , wherein the semi-noble metal layer comprises ruthenium. 
     
     
         14 . The method of  claim 1 , wherein at least some of the features have a width of about 100 nm or less. 
     
     
         15 . The method of  claim 14 , wherein at least some of the features have a width of about 20 nm or less. 
     
     
         16 . The method of  claim 1 , wherein the electrolyte comprises about 2 ppm or less dissolved oxygen. 
     
     
         17 . A method of performing a one step electrofill process to fill features on a partially fabricated integrated circuit, comprising:
 (a) receiving a substrate having an exposed semi-noble metal layer and a plurality of features thereon;   (b) contacting the substrate with electrolyte comprising between about 1-100 mM copper cations, wherein the electrolyte is substantially free of suppressors, accelerators and levelers; and   (c) while contacting the substrate with electrolyte, applying a modulated waveform that alternately pulses current at a first level that deposits copper on the substrate and a second level that etches copper from copper that was previously electroplated on the substrate, to thereby electroplate copper into the features by a bottom-up fill mechanism at a substrate potential for electrodeposition between about 0.03 and 0.33 V versus an NHE reference electrode.   
     
     
         18 . The method of  claim 17 , wherein the second level of current that etches copper has an absolute value between about 0.05 and 0.3 mA/cm 2 , and wherein the pulses of current alternate between the first current level and second current level with a frequency between about 100-1000 Hz. 
     
     
         19 . A method of depositing copper in a feature on a partially fabricated integrated circuit, comprising:
 (a) receiving a substrate having a plurality of features and a copper seed layer thereon;   (b) contacting the substrate with electrolyte comprising between about 1-100 mM copper cations, wherein the electrolyte is substantially free of suppressors, accelerators and levelers; and   (c) electroplating copper into the feature by a bottom-up fill mechanism at a potential between about 0.03 and 0.33 V versus an NHE reference electrode.   
     
     
         20 . The method of  claim 19 , wherein, during electroplating, the electrolyte is held at a temperature between about 20-80° C. 
     
     
         21 . The method of  claim 20 , wherein, during electroplating, the electrolyte is held at a temperature between about 20-50° C. 
     
     
         22 . The method of  claim 19 , wherein, during electroplating, the electroplating surface of the substrate has a current density of between about 0.1-2 mA/cm 2 . 
     
     
         23 . The method of  claim 19 , wherein a pH of the electrolyte is between about 1-5. 
     
     
         24 . The method of  claim 19 , at least some of the features have a width of about 100 nm or less. 
     
     
         25 . The method of  claim 24 , at least some of the features have a width of about 20 nm or less. 
     
     
         26 . The method of  claim 19 , wherein electroplating copper in operation (c) comprises applying a galvanostatically controlled current to the substrate. 
     
     
         27 . An apparatus for electroplating copper into features on a substrate, comprising:
 (a) one or more electroplating baths configured to contain electrolyte;   (b) a substrate supporter; and   (c) a controller having a set of instructions comprising instructions for:
 receiving electrolyte into the one or more electroplating baths; 
 immersing the substrate in electrolyte; 
 maintaining a substrate potential between about 0.03-0.33 V versus an NHE reference electrode to thereby electroplate copper into the features by a bottom-up fill mechanism that does not substantially rely on the presence of suppressor, accelerator or leveler.