USING CVS FOR PLATING BATH ANALYSIS
Figure 1 is an actual display from the QUALILAB Plating Bath Analyzer. The potential determines the electrochemical reaction that occurs. The potential is displayed on the X-axis with potentials becoming more positive from left to right. A positive-going potential is becoming more strongly oxidizing, while a negative going potential generates a more strongly reducing condition. Current is shown on the Y-axis. A positive current corresponds to an oxidation while a negative current is due to a reduction. The voltammogram has several regions of interest:
In general, additives such as levelers or wetters act as suppressors and decrease the plating rate while brighteners increase the rate of deposition. Use caution, however, since there is no standard terminology for additives within the industry.
During electroplating, the organic additives undergo various chemical transformations such as oxidation, reduction, fragmentation, and polymerization. Most of the products of such transformations also affect the plating process. CVS provides a measure of the effective concentration of additive (the activity of the additive in terms of the fresh additive) which is more important than the concentration of a specific substance. Most analytical techniques (spectroscopy, HPLC) measure absolute concentration. The transformed additive will still be electroactive, but not responsive to spectroscopy, or vice versa. Because CVS is based on the plating process, it is the only technique that provides a true measure of the activity of the organic additives.
DETERMINATION OF ADDITIVES AND THEIR COMPONENTS
The quantitative determination of organic additives is based on the CVS response of the production bath before and after the addition of a known amount of a standard. The fresh additive as supplied by the manufacturer, which is used for replenishment of the bath, is used as the standard. Since the fresh additive is used as the standard, the concentration of additive in the production bath is expressed as the equivalent activity of the fresh additive. In this way, replenishment of the bath to the proper additive level is very convenient.
It is usually possible to quantify all of the additives in the plating bath. An example of an acid copper bath is shown in Figure 3.
The carrier acts as a suppressor and inhibits the rate of the plating process. This can be seen from the reduction in peak area as the concentration of the carrier is increased. Notice that the activity of the carrier is very high, i.e., a small increase in concentration has a large effect on the rate of plating. The fresh carrier as supplied by the manufacturer was used to spike the solution.
The plating rate changes dramatically as the carrier is increased from 0-1 mL/L. As the carrier concentration is increased beyond 1 mL/L, there is little additional effect on the plating rate.
The brightener has a different effect. In the presence of carrier, higher brightener concentration causes an increase in plating rate. The activity of the brightener is lower than the carrier. The difference in activity between the carrier and the brightener can be exploited to quantify both components.
Some manufacturers offer a pre-mixed solution containing both the carrier and the brightener. These components can be clearly distinguished in Figure 3. CVS can be employed to insure that the carrier and the brightener are in balance in the production bath.
The analysis of plating baths using CVS benefits from experience. ECI Technology has invested over 15 years in developing CVS methods for a wide variety of plating baths. In addition to manufacturing CVS instrumentation, ECI Technology is the leading source of CVS applications information. CVS consultation is available to every user of ECI Technology products.
OUTGOING AND INCOMING INSPECTION OF ADDITIVES
CVS is a powerful tool for the outgoing inspection of additives by suppliers as well as incoming inspection at users’ sites. Figure 4 illustrates the variations between several lots of the same brightener.
By performing a fast, easy assay, the user avoided under dosing or overdosing the brightener and losing control of the bath.
THE INDUSTRY STANDARD
Since its initial development in the late 70’s, CVS has experienced tremendous growth. The contributions of CVS to both suppliers and users of plating chemistries has been significant. This patented technology is currently used by all major chemistry suppliers for quality control or routine analysis of customers’ baths. ECI Technology is the major driving force behind CVS. The development of both CVS instrumentation and analytical procedures by ECI Technology has been a critical contribution to the growth of CVS.
Users of CVS instrumentation from ECI Technology include the most trusted manufacturers of semiconductors and printed wiring boards such as Motorola, IBM, Intel, Texas Instruments, Northrop, Tyco, Photocircuits, Sanmina, and others. CVS may be found in plating laboratories in the Americas, Europe, and Asia. In addition the innovative engineering of ECI Technology was recognized by an R&D 100 Award.
APPLICATIONS OF CVS
Prevention of plating problems by quantitative measurement of the organic additives in plating solutions keeps the chemistry in balance.
• Quantitative determination of additives and their components
• Individual fingerprints of plating solutions
• Incoming/outgoing inspection of plating additives
• Monitoring the level of plating solution contamination
• Scheduling baths for carbon treatment and optimizing of the treatment
Study, develop, and optimize new plating technology
• Study the effect of various parameters of the plating process (concentration of additives, current density, mass transport, temperature, etc.) on the performance of plating solutions
• Study the consumption and transformation of additives during the plating process
• Study the effect of various additives on the plating process
1Cyclic Volatmmetric Stripping (CVS) is a patented technology. QUALILAB QL-5 is a trademark of ECI
Technology, Inc. No part of this material may be copied, used or distributed in whole or in part without
permission from ECI Technology, Inc.