Cyclic voltammetric method for the measurement of concentrations of subcomponents of plating solution additive mixtures

• US 5,192,403 A
• Filed: 05/16/1991
• Issued: 03/09/1993
• Est. Priority Date: 05/16/1991
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Horkans, Wilma J., Chang, I-Chia H.
• Primary Examiner(s): Niebling, John
• Assistant Examiner(s): Bell, Bruce F.
• Application Number:
  US07/701,278
• Time in Patent Office: 663 Days
• Field of Search: 204/153.1, 204/402, 204/434
• US Class Current: 205/794.5
• CPC Class Codes: G01N 27/42 Measuring deposition or liberation of materials from an electrolyte; Coulometry, i.e. measuring coulomb-equivalent of material in an electrolyte

Abstract

A cyclic voltammetric method for measuring concentrations of subcomponents of additive mixtures, comprising the steps of: (a) preparing a basis solution which contains all of the components of an unknown solution to be measured, except a component of interest; (b) preparing a calibration solution which contains the component of interest in a known concentration near that which would be expected in the unknown solution; (c) adding measured amounts of the calibration solution to a first defined volume of the basis solution and plotting a first cathodic charge against the added volume of the calibration standard; (d) adding measured amounts of the unknown solution to a second volume of the basis solution and plotting a second cathodic charge against the added volume of the unknown solution; and (e) comparing the slopes of the first and second curves to determine the concentration of the component of interest in the unknown solution.

Claims

1. A cyclic voltammetric method for measuring concentrations of subcomponents of additive mixtures, comprising the steps of:

(a) preparing a basis solution which contains all of the components of an unknown solution to be measured, except a component of interest;

(b) preparing a calibration solution which contains said component of interest in a known concentration near that which would be expected in said unknown solution;

(c) adding measured amounts of said calibration solution to a first defined volume of said basis solution;

(d) applying an electrical potential to an electrode in the mixed calibration/basis solution and plotting the calibration cathodic charge against the added volume of the calibration solution;

(e) adding measured amounts of said unknown solution to a second volume of said basis solution;

(f) applying an electrical potential to an electrode in the mixed unknown/basis solution and plotting the cathodic charge against the added volume of the unknown solution; and

(g) comparing the slopes of the calibration and unknown cathodic charge versus volume curves to determine the concentration of said component of interest in said unknown solution.

2. A method according to claim 1, comprising the further steps of:

(h) applying said electrical potential in each of steps (d) and (f) cyclically between predetermined positive (E_a) and negative (E_c) potentials at a predetermined cycling rate; and

(i) measuring the respective charge readings of said mixed calibration/basis solution and said mixed unknown/basis solution following each full cycle of applied electrical potential.

3. A method according to claim 2, comprising the further steps of:

(j) applying said electrical potential in step (d) a predetermined number of times or until a stable charge reading is obtained; and

(k) measuring the charge reading of said calibration/basis solution with each application of said electrical potential.

4. A method according to claim 3, comprising the further steps of:

(l) applying said electrical potential in step (f) a predetermined number of times or until a stable charge reading is obtained; and

(m) measuring the charge reading of said unknown/basis solution with each application of said electrical potential.

5. A cyclic voltammetric method for determining additive components in a mixture of additives in a plating solution, comprising the steps of:

(a) preparing a basis solution containing all components of the plating solution except the one component to be analyzed in an electrochemical cell containing an electrode to which an electrical potential may be applied;

(b) adding a predetermined amount of a standard solution containing a known amount of the one component to be analyzed to said basis solution;

(c) thereafter applying an electrical potential to an electrode in said electrochemical cell following step (b) a predetermined number of times or until a stable charge reading is obtained;

(d) repeating steps (b)-(c) a predetermined number of times;

(e) plotting the value of the charge read in step (c) versus the volume of said standard solution added to said basis solution as a result of the repetition of step (b) to obtain a graphical plot having the slope dQ/dV for said standard solution;

(f) adding to said basis solution a predetermined amount of said working solution containing an unknown amount of the one component to be analyzed;

(g) thereafter applying an electrical potential to said electrochemical cell following step (f) a predetermined number of times or until a stable charge reading is obtained;

(h) repeating steps (f)-(g) a predetermined number of times; and

(i) plotting the value of the charge read in step (g) versus the volume of said working solution added to said basis solution as a result of the repetition of step (f) to obtain a graphical plot having the slope dQ/dV for said working solution;

(j) comparing the slopes of said standard and working solutions determined from steps (e) and (i) to determine the concentration of said one component in said working solution.

6. A method according to claim 5, comprising the further steps of:

(k) applying said electrical potential in each of steps (c) and (g) cycling between predetermined positive (E_a) and negative (E_c) potentials at a predetermined cycling rate; and

(l) measuring the respective charge readings of said mixed calibration/basis solution and said mixed unknown/basis solution, following each full cycle of applied electrical potential.

7. A method according to claim 6, further comprising the steps of:

(m) adding in step (b) said predetermined amount of standard solution to a first defined volume of said basis solution; and

(n) adding in step (f) said predetermined amount of working solution to a second volume of said basis solution, such that the amount of working solution added to said second volume is in direct proportion to the amount of standard solution added to said first volume.