Method for monitoring metal ion concentrations in plating baths

• US 4,725,339 A
• Filed: 02/13/1984
• Issued: 02/16/1988
• Est. Priority Date: 02/13/1984
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Light, David N., Bindra, Perminder, Levine, Solomon L.
• Primary Examiner(s): Kaplan, G. L.
• Application Number:
  US06/579,733
• Time in Patent Office: 1,464 Days
• Field of Search: 204/1 T, 204/434, 204/412, 427/8, 427/10, 364/497, 364/499, 364/500
• US Class Current: 205/81
• CPC Class Codes: G01N 27/48 using polarography, i.e. measuring changes in current under a slowly-varying voltage
• CPC Class Codes: G01N 27/49 Systems involving the determination of the current at a single specific value, or small range of values, of applied voltage for producing selective measurement of one or more particular ionic species

Abstract

A rotating disk electrode system operates at constant speed in a solution whose metal ion concentration is held constant at multiple concentrations within a range of concentration. The current at the working electrode is recorded, while the potential at the working electrode is swept at a predetermined rate for each of the concentration values. The diffusion limiting current is determined for each of the concentration values. Then the rotating disk electrode system is operated continuously in a metal plating bath whose metal ion concentration can vary. A voltage applied to the working electrode produces a current at the electrode whose magnitude is compared to the values of the previous calibration to determine the current metal ion concentration. Alternatively, a rotating disk electrode system is operated over a range of speeds in a solution whose ion concentration is held constant over a range of concentration. Current at the working electrode is measured for a given electric potential applied to the working electrode. In this way, a calibration relationship between the current at the electrode and the range of metal ion concentrations is established which can be used with current measured in the plating bath under the same conditions as those that established the calibration curve to predict the concentration of the bath.

Claims

1. A method for monitoring the concentration of metal ions in a metal plating bath used for metal deposition on a substrate comprising:

operating a rotating disc electrode system in a solution having a concentration of metal ions of the type to be deposited, the system including a working electrode, a counter electrode and a reference electrode;

applying electric potential of variable magnitude between the working electrode and the reference electrode while maintaining the metal ion concentrations of the solution constant at various concentrations within a range of said concentrations;

determining the diffusion limiting currents during metal plating at the working electrode corresponding to said various ion concentrations;

operating a rotating disc electrode system in the metal plating bath;

recording the diffusion currents that result from applying an electric potential between the working electrode and the reference electrode; and

determining the metal ion concentration in the plating bath from the relationship between the metal ion concentrations and the corresponding diffusion limiting currents previously established from the solution.

2. A method for monitoring the concentration of metal ions in a metal plating bath used for metallic deposition on a substrate comprising:

operating a rotating disc electrode system in a solution having a variable concentration of metal ions of the type to be deposited, the system including a working electrode, a counter electrode and a reference electrode;

determining, for various constant metal ion concentrations in the solution, the electrical current during metal plating in working electrode that results from applying electrical potential to the working electrode with respect to the reference electrode and varying the speed of the rotating disc electrode system through a range of speed while the metal ion concentration is held constant;

determining, from the electrical currents and said speeds, the relationship between the limiting currents and the corresponding metal ion concentrations;

operating a rotating disc electrode system in the plating bath;

determining the limiting current during metal plating in the working electrode of the rotating disc electrode system that results from applying electric potential to the working electrode with respect to the reference electrode; and

determining from the limiting current of the plating bath the metal ion concentration of the plating bath from the relationship between the limiting currents and the metal ion concentrations established from the solution

3. A method for monitoring the concentration of metal ions in a metal plating bath used for metallic deposition on a substrate comprising:

operating a rotating disc electrode system in a solution having a variable concentration of metal ions of the type to be deposited, the system including a working electrode, a counter electrode and a reference electrode;

determining, for various constant metal ion concentrations of the solution, the electrical current during metal plating in the working electrode that results from applying electrical potential to the working electrode with respect to the reference electrode and varying the speed of the rotating disc electrode system through a range of speed while the metal ion concentration is held constant;

determining the diffusion parameters and the kinetic currents that correspond to the various metal ion concentrations of the solution from the relationships between the electrical currents in the working electrode and the speeds of the rotating disc electrode system;

determining, from the diffusion parameters and the kinetic currents, the limiting currents that correspond to the metal ion concentrations of the solution;

operating a rotating disc electrode system in a plating bath;

determining the electrical current in the working electrode that results from applying electrical potential to the working electrode with respect to the reference electrode and varying the speed of the rotating disc electrode system through a range of speed;

determining the diffusion parameter and the kinetic current of the plating bath from the relationship between the electrical current in the working electrode and the speed of the rotating disc electrode system;

determining, from the diffusion parameter and the kinetic current, the limiting current that corresponds to the metal ion concentration of the plating bath; and

determining from the limiting current of the plating bath the metal ion concentration of the plating bath from the relationship between the limiting currents and the metal ion concentrations established from the solution.

4. The method of claim 3 wherein determining the diffusion parameters that correspond to the various metal ion concentrations of the solution comprises:

establishing for the various metal ions concentrations of the solution the relationship between the electrical current in the working electrode and the corresponding speed of the rotating disc electrode system; and

determining for the various metal ion concentrations of the solution the slope of the straight line that passes through the mean of the reciprocals of the electrical current in the working electrode and the corresponding speed of the rotating disc electrode system.

5. The method of claim 4 wherein determining the limiting currents i that correspond to the various metal ion concentrations of the solution comprises:

determining the magnitude of the kinetic current i as the intercept of the reciprocal of the electrical current axis by said straight line; and

calculating the limiting current i from the relationship ##EQU7## where B is the diffusion parameter of the solution and ω

is the speed of the rotating disc electrode system.