Protocols require that once a wafer has entered a copper bay, it cannot return to a noncopper bay. Sources of Copper Contamination Contamination can arise from tools and equipment involved in the deposition and handling of wafers. For example, a deposition tool that coats wafers with copper films may deposit copper on the bevel of the wafer. This wafer may then be sent to a metrology tool equipped with a wafer handler that manipulates the edges of wafers processed in various areas of the fab. This wafer handler, contaminated with copper, can then cross-contaminate wafers that are destined for an etch tool.
Contamination can also spread by way of the wafer's backside.
Many wafer handlers, or robots, grab or lift wafers by their backsides. The damascene or dual-damascene process affords devices a certain measure of protection against copper contamination. Copper diffusion barriers such as tantalum nitride, titanium nitride, and insulating silicon nitride provide on-chip protection against copper migration from interconnect structures to neighboring dielectrics and silicon. These materials are widely used in the copper damascene process architecture, effectively encapsulating every single interconnect, as illustrated in Figure 2. Frontside layers and processes, however, do not sufficiently protect devices against external sources of copper that may contaminate the bevel and backside regions of the wafer.