Method For Extending Etch Bath Or Plating Bath Life And Increasing Tool Performance
Original Publication Date: 2002-May-20
Included in the Prior Art Database: 2003-Jun-20
In nickel-iron etch baths, the quality of the etch chemistry is critical to controlling the etch rate. As the bath degrades, the etch rate degrades also. In order to compensate for this degradation, etch time must be increased. This causes variations in batch-to-batch runs and requires constant running of etch rate monitors. These monitors, in turn, decrease the quality of the chemistry further and decrease the thruput of the tool. Adding in the increased time for etching production wafers decreases the thruput of the station even further. If the etch rates are not carefully monitored, residual material is left on the wafers. This, depending on the operation, can cause scrap or rework. When wafers have to be reworked, the station thruput is decreased even further. Therefore, bath chemistry has a compounding effect on the station thruput and wafer quality. By adding hardware and software to control a gaseous purge of both the bath chemistry tank and the processing chamber, etchant life can be extended and tighter control of batch-to-batch operations are possible. Different gases are used for different chemistries. In the NiFe etch process, there are two components to the etch operation: NiFe etchant and NiFe activator. The etchant and activator are sprayed into the chamber individually in different steps. The etchant would add a bubbler to the tank and a purge to the process chamber using Clean Dry Air. Opposite of this scheme is the activator, which requires clean, pure, nitrogen. The nitrogen would be bubbled through the tank and used to purge the process chamber, in the same manner as the CDA. Both of these gases will extend the life of the particular chemistry by removing unwanted gases from being in contact with the chemistry and performing an actual beneficial chemical conversion. In the etch activation portion of the operation, the bath chemistry is sprayed into the process chamber. In a fine spray through the many nozzles in the chamber, the chemistry now has greater surface area exposed to the air in the process chamber. This increases the rate of chemical degradation. The additional hardware and software control to be added to the tool would allow nitrogen to purge all of the air out of the chamber in the activation phase of the process. Once the nitrogen has displaced the air, the activation phase of the etching would begin. At this point in the process, the chemistry would not be in contact with any oxygen, thus greatly reducing the oxidation and degradation of the chemistry. In the case of the etchant, oxygen in the air is a desirable gas in order to regenerate the chemistry. Ideally, the etchant would be 100% in the FE (III) state, as this is the active etching species. As the chemistry degrades and the Fe (III) is converted to Fe (II), the etchant is weaker and takes an increasingly longer amount of time to etch the same thickness of material on the wafer. By introducing CDA into the reservoir and purging the process chamber with only CDA at this step of the operation, the Fe (II) is converted back into Fe (III).