Page 258 - Semiconductor Manufacturing Handbook

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CHEMICAL MECHANICAL POLISHING

CHEMICAL MECHANICAL POLISHING 17.13

Pressure
gauge
Pressure
P
gauge
P Flow
valve
Flow meter
Filtration
element
Heat
exchanger Permeate
Flow
valve
Pressure
P
gauge
Flow Valve
valve Feed
tank Drain

Centrifugal pump

The pH of the sample was adjusted manually prior to solids removal
with the ceramic membranes.
FIGURE 17.5 Modern Cu CMP Effluent Cleaning system. (Source: R. Woodling, www.semi.org.)

*
filters, like those made by US Filter for Cu CMP effluents, can usually filter down to 0.02 µm. Post-
processing of Cu CMP residues after filtering is typically completed using precipitation, ion
exchange, and electrochemistry to eliminate Cu. In general, these techniques will generate solid
toxic wastes that will have to be stored and removed for the facility. Both academic and industrial
research continue to improve Cu CMP effluent management. An advanced Cu CMP effluent man-
agement system by US Filter is illustrated in Fig. 17.5.

17.7 FUTURE TRENDS AND CONCLUSIONS

CMP is an elegant way of etching films while simultaneously flattening them to atomic levels. The
process also works for a wide variety of films and applications. Newer CMP tools are now very reli-
able. CMP tools and consumables industries have both made many improvements over the last 20
years. The process is DI water intensive and can generate some manageable toxic wastes. Overall,
CMP is a good way to help resolve depth-of-focus issues with lithography while also bringing Cu
into advanced microelectronics.
As CMP tools advance into the 70 nm and smaller process nodes, they will encounter softer,
porous, low-k dielectric (constant) materials and fluoro-silicate glasses (FSGs). These films are so
delicate that they can actually be crushed by the capillary forces resulting from drying water.
Polishing-generated friction and chemicals can easily damage low-dielectric constant films. In order
to reduce polishing-related shear forces, applied polishing downforce is reduced and the table (pad)
speed is increased to bring up material removal rates. Polishing near the hydroplaning regime is helpful
for improving planarization efficiency and reducing polishing shear friction forces. In these “gentle”
CMP tools, efficient fluid transport of slurry to and from the wafer and gentle downforce control

* Woodling, R., “Treatment of Copper CMP Wastewater Without Hazardous Waste Generation,” SEMI.ORG Web Site, 2003.

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