Simultaneous inorganic, organic and byproduct analysis in electrochemical deposition solutions

Abstract

Real-time analysis of electrochemical deposition (ECD) metal plating solutions is described, for the purpose of reducing plating defects and achieving high quality metal deposition. Improved plating protocols are utilized for increasing potential signal strength and reducing the time required for each measurement cycle. New methods and algorithms for simultaneously determining concentrations of organic additives, inorganic additives, and/or byproducts in a sample ECD solution are described. In one aspect, a method is provided for simultaneously determining concentrations of all organic additives, inorganic additives, and/or byproducts within a single experimental run by using a single analytical cell, while interactions between such additives are properly accounted for.

1 . A method for simultaneously determining concentrations of copper sulfate, sulfuric acid, chloride ion, suppressor, accelerator, leveler, and/or byproduct(s) thereof in a sample electrochemical deposition solution, comprising the steps of: 
 (a) identifying one or more non-compositional variables that affect electropotential responses of electrochemical deposition solutions during electrochemical metal deposition;    (b) establishing a multiple regression model that expresses the electropotential responses of electrochemical deposition solutions as a function of (1) said one or more non-compositional variables, (2) organic additive concentrations in the solutions, (3) inorganic additive concentrations in the solutions, (4) byproduct concentrations in the solutions, and the corresponding coefficients;    (c) conducting multiple calibration runs, by measuring electropotential responses of multiple calibration solutions having unique, known organic additive, inorganic additive, and/or byproduct concentrations at unique, predetermined values of said one or more variables;    (d) determining the coefficients that correspond to said one or more variables and the organic additive, inorganic additive, and/or byproduct concentrations in the multiple regression model, based on information obtained from the calibration runs; and    (e) conducting N experimental runs, by measuring electropotential responses of the sample electrochemical deposition solution at unique, predetermined values of said one or more variables;    (f) establishing N number of equations based on the established multiple regression model, said equations containing the coefficients determined in step (d), the electropotential responses measured during the N experimental runs in step (e) and the corresponding predetermined values of said one or more variables, and the unknown concentrations of the copper sulfate, sulfuric acid, chloride ion, suppressor, accelerator, leveler, and/or byproduct(s) thereof in the sample electrochemical deposition solution; and    (g) calculating said copper sulfate, sulfuric acid, chloride ion, suppressor, accelerator, leveler, and/or byproduct concentrations in the sample solution by solving the N equations provided in step (f).    
   
   
       2 . The method of  claim 1 , wherein said one or more non-compositional variables are identified by conducting analysis of variance tests on all non-compositional variables having potential impact on electropotential responses of electrochemical deposition solutions and selecting those variables having non-zero coefficients at confidence levels that are not less than 95%.  
   
   
       3 . The method of  claim 1 , wherein said one or more non-compositional variables are selected from the group consisting of (1) nucleation potential, (2) nucleation time, (3) electroplating current, (4) electroplating time, (5) scan rate of the cyclic voltammetry during pre-plating cleaning process, and (6) size of the measuring electrode used for conducting the electrochemical metal deposition.  
   
   
       4 . The method of  claim 1 , wherein said multiple regression model includes terms that account for interactions (1) between said non-compositional variables, (2) between the organic additive concentrations, (3) between the inorganic additives, (4) between the byproduct(s) and/or (5) between one or more non-compositional variables and one or more organic additive, inorganic additive, and/or byproduct concentrations.  
   
   
       5 . The method of  claim 1 , wherein in step (e), said N experimental runs are conducted in N different electrochemical analytical cells, wherein each cell performs electropotential measurements on the sample electrochemical deposition solution according to a unique, predetermined plating protocol.  
   
   
       6 . The method of  claim 5 , wherein each plating protocol differs from the other two by at least one factor selected from the group consisting of (1) nucleation potential, (2) nucleation time, (3) electroplating current, (4) electroplating time, (5) scan rate of the cyclic voltammetry during pre-plating cleaning process, and (6) size of the measuring electrode used for conducting the electrochemical metal deposition.  
   
   
       7 . The method of  claim 1 , wherein N is in a range from about 3 to about 10.  
   
   
       8 . The method of  claim 1 , wherein N is 7.  
   
   
       9 . The method of  claim 1 , wherein the byproduct comprises copper (I) thiolate.  
   
   
       10 . A method for simultaneously determining concentrations of copper sulfate, sulfuric acid, chloride ion, suppressor, accelerator, leveler, and/or byproduct(s) thereof in a sample electrochemical deposition solution, by using a single electrochemical analytical cell and a single plating protocol, comprising the steps of: 
 (a) selecting n compositional terms that include copper sulfate concentration, sulfuric acid concentration, chloride ion concentration, suppressor concentration, accelerator concentration, leveler concentration, byproduct(s) concentrations, and interactions between two or more of said concentrations, wherein n≧3;    (b) establishing m multiple regression models that correspond to m time points during the electrochemical metal deposition process, wherein each model expresses electropotential responses of electrochemical deposition solutions as a function of the n selected compositional terms and their corresponding coefficients, wherein m≧3;    (c) using said electrochemical analytical cell and said plating protocol for measuring electropotential responses of multiple calibration solutions at each of said m time points, wherein said calibration solutions contain copper sulfate, sulfuric acid, chloride ion, suppressor, accelerator, leveler, and/or byproduct(s) at unique, known concentrations;    (d) determining the coefficients of said n selected compositional terms for each of the m multiple regression models, based on information obtained in step (c);    (e) using said electrochemical analytical cell and said plating protocol for measuring electropotential responses of the sample electrochemical deposition solution at each of said m time points; and    (f) determining the n selected compositional terms based on the established multiple regression models, the coefficients determined in step (d), and the electropotential responses measured in step (e); and    (g) calculating concentrations of copper sulfate, sulfuric acid, chloride ion, suppressor, accelerator, leveler, and/or byproduct(s) in the sample electrochemical deposition solution from the compositional terms so determined.    
   
   
       11 . The method of  claim 10 , wherein in step (f), the n selected compositional terms are determined by: 
 (i) establishing three matrices X, β, and Y to represent the m multiple regression models as Y=βX, wherein X is a n×1 compositional matrix containing the n compositional terms, wherein β is a m×n coefficient matrix containing the coefficients determined in step (d), and Y is a m×1 response matrix containing the electropotential responses measured in step (e); and    (ii) determining the compositional matrix X as:        X =(β′β) −1   β′Y      wherein β′ is the transpose of β, and wherein (β′β) −1  is the inverse of β′β.    
   
   
       12 . The method of  claim 10 , wherein said compositional terms are selected by conducting analysis of variance tests on all linear, quadratic, and cubic terms related to the copper sulfate, sulfuric acid, chloride ion, suppressor, accelerator, leveler, byproduct(s) concentrations and interactions therebetween regarding their potential impact on electropotential responses of electrochemical deposition solutions, and selecting those terms having non-zero coefficients at confidence levels that are not less than 95%.  
   
   
       13 . The method of  claim 10 , wherein 3 multiple regression models corresponding to 3 time points during the electrochemical metal deposition process are established.  
   
   
       14 . The method of  claim 13 , wherein said three time points are selected from the group consisting of 0.2 second, 0.25 second, 0.5 second, 1 second, 5 seconds, 10 seconds, and seconds, as measured from the initiation of the electrochemical metal deposition process.  
   
   
       15 . The method of  claim 10 , wherein the byproduct comprises copper (I) thiolate.  
   
   
       16 . A method for simultaneously determining concentrations of inorganic additives, suppressor, accelerator, leveler, and/or byproduct(s) thereof in a sample electrochemical deposition solution, comprising the steps of: 
 (a) identifying one or more non-compositional variables that affect electropotential responses of electrochemical deposition solutions during electrochemical metal deposition;    (b) establishing a multiple regression model that expresses the electropotential responses of electrochemical deposition solutions as a function of (1) said one or more non-compositional variables, (2) organic additive concentrations in the solutions, (3) inorganic additive concentrations in the solutions, (4) byproduct concentrations in the solutions, and the corresponding coefficients;    (c) conducting multiple calibration runs, by measuring electropotential responses of multiple calibration solutions having unique, known organic additive, inorganic additive, and/or byproduct concentrations at unique, predetermined values of said one or more variables;    (d) determining the coefficients that correspond to said one or more variables and the organic additive, inorganic additive, and/or byproduct concentrations in the multiple regression model, based on information obtained from the calibration runs; and    (e) conducting N experimental runs, by measuring electropotential responses of the sample electrochemical deposition solution at unique, predetermined values of said one or more variables;    (f) establishing N number of equations based on the established multiple regression model, said equations containing the coefficients determined in step (d), the electropotential responses measured during the N experimental runs in step (e) and the corresponding predetermined values of said one or more variables, and the unknown concentrations of the inorganic additives, suppressor, accelerator, leveler, and/or byproduct(s) thereof in the sample electrochemical deposition solution; and    (g) calculating said inorganic additives, suppressor, accelerator, leveler, and/or byproduct concentrations in the sample solution by solving the N equations provided in step (f).    
   
   
       17 . The method of  claim 16 , wherein the inorganic additives comprise a copper salt.  
   
   
       18 . The method of  claim 16 , wherein the inorganic additives comprise copper sulfate.  
   
   
       19 . The method of  claim 16 , wherein the inorganic additives comprise sulfuric acid.  
   
   
       20 . The method of  claim 16 , wherein the inorganic additives comprise chloride ion.