Slurry Distribution Systems

The need for a reliable source of slurry during CMP stimulated the growth of a whole industry of bulk chemical distribution (BCD) systems. An extended discussion of BCD systems is beyond the scope of this work, but a few words are in order. Slurry distribution systems vary in sophistication from the simple laboratory system consisting of little more than a barrel of slurry and a pump to sophisticated delivery systems designed to supply slurry to tens of CMP tools in a high-volume production environment [56]. 

A slurry distribution system is a part of the infrastructure of a semiconductor fab, rather than a stand-alone piece of equipment. Even so, it can be thought of as a collection of pieces that comprise the whole. Many of these individual components can be sized for the specific system or left out... 

Support facilities and services associated with the slurry distribution system may include... 

Fig. 1. Generalized CMP slurry distribution system with metrology, assay control, and filtration.

Similar to oxide CMP, a basic W CMP process uses a polisher equipped with a polishing pad, a cleaning unit, and a slurry distribution system. Owing to the need for an oxidizer, the slurry distribution system also includes a premixing sequence. As the lifetimes of these oxidizers are usually short, the... 

The data on lot 2 of day 9 showed a wide process variation (endpoint time increase) from the previous set of data. An analysis of the CMP status log with the endpoint data indicated that slurry was not being pumped to the pads on the tool. The problem was not detected until two hours after it occurred. The root cause was traced to software issues in the slurry distribution system. Note Real-time endpoint control with set specification limits would have resulted in a warning at the time of excursion. Observation over a three day period examining two lots per day and three wafers from each lot (Figure 4), showed that half of the total variation is explained by lot differences. Wafer-wafer variation within a lot is significantly smaller than between lots. 

---