On-Line Monitoring of Inorganic Additives in Copper Electroplating Baths

摘要

Since it has been established that selective electrodes can serve as detectors for both ammonia and chloride, their implementation for on-line monitoring must be addressed. With materials and chemical processes varying from house to house, the environment of the on-line sensors must be considered, particularly where interfering chemical agents are present. Also, the mechanics of the process require investigation. For instance, with chloride the measurement is direct; however, for ammonia determination a strong caustic reagent must be added to the bath solution to evolve ammonia gas which is then measured. By adding only the caustic reagent to the copper pyrophosphate bath, cupric hydroxide is formed and precipitates while ammonia is released. Under such a condition, the delivery line from the analysis area to waste will become clogged and will cause controller malfunction. In the case of the caustic reagent for copper pyrophosphate, the presence of cyanide as a complexing agent allows ammonia to be evolved but precludes precipitation of cupric hydroxide. Automatic monitors for both chloride and ammonia are commercially available (Orion Research Corp.) but monitoring/replenishing systems such as electroless bath analyzers are not available for either the copper pyrophosphate or acid copper sulfate baths. As a result, each multilayer board fabrication house is left with the decision whether or not to perform only monitoring or to interface their pH/mV meter to a microprocessor/data controller with feedback which will activate valves and pumps for a period of time based upon the pH/mV meter reading. In brief, the selective electrode monitoring of inorganic additives such as ammonia and chloride proved feasible, and in some cases, considerably more reliable than monitoring by wet chemical methods.