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CHEMICAL MECHANICAL POLISHING

17.12 WAFER PROCESSING

driven by motors. The wafer carrier is stationary and centered on the track. It can be rotated slowly
to “smooth” and further polishing uniformity. These systems produce an ideally uniform velocity
field across the wafer surface. Slurry distribution consists of an array of sprayers pointed at the pad.
A linear diamond-coated bar placed against the pad completes the pad conditioning. This allows for
in situ pad conditioning. The most famous of these linear CMP tools is the Teres platform developed
by LAM Research Corporation. The Teres platform has a horizontal pad configuration. The second
linear drive tool, and less well known, was the twin head APLEX tool. The APLEX system is unique
in that it uses a vertical pad configuration to reduce the tool footprint.
Linear CMP tools were fairly successful for oxide CMP, but lacked the multiplaten flexibility for
Cu CMP. Both linear tools used front referencing carriers at one time or the other, and fluid bearing
systems to improve polishing uniformity. Unlike the Aplex CMP tool, the LAM Teres platform was
actually used in a production environment. Due to poor process flexibility, reliability problems, and
adverse business conditions, these tools did not survive long in the industry.

17.6 CMP PROCESS WASTE MANAGEMENT

CMP tools use both benign and hazardous chemicals. For the most part, CMP tools use copious amounts
of DI water for wafer processing. By volume, DI water is the most predominant effluent from CMP
tools. In addition to DI water, CMP process effluents can contain a multitude of constituents such as
ammonia, dilute hydrofluoric acid, KOH, hydrogen peroxide, ferric nitrite oxidizers, metallic residues,
and possibly silica, alumina, and/or ceria particulates. Strategies for elimination of CMP process wastes
depend on meeting local laws and environmental regulations.
CMP tool waste streams are normally separated by process modules. Mixing process effluents from
a CMP tool is not a good idea, since CMP cleaning chemistries can be very reactive with polishing
chemistries. In addition, some oxidizers such as ferric nitrate can discolor CMP tool plastic components
and attack steels used to frame the tool. In general, CMP tool components are very corrosion resistant.
Therefore, improper management of CMP tool waste can impact tool reliability due to corrosion or
reactivity issues.

17.6.1 Oxide CMP Process Waste

Oxide CMP slurry systems are KOH-based and contain solids like silica and ceria. An array of
fibrous and ceramic filters can remove solids from the process effluent of the CMP tool. Additions
of weak acids to KOH will generate potassium salts while neutralizing the solution to a pH of about
6 to 7. Oxide CMP waste streams are also free of metallic contamination; therefore they are typically
environmentally benign after filtering and neutralization. Typical HF neutralization systems used for
processing acid wastes can handle CMP cleaning system effluents from ILD or STI CMP tools.
Though dangerous or aromatic in their diluted state, CMP cleaning chemistries can be neutralized
and processed much like wet etch station effluents.

17.6.2 Metal CMP Process Waste

Metallic CMP effluents are far more of a concern in the fab. Cu CMP is the most toxic of the CMP
processes since ionic Cu is a common process effluent along with a variety of oxidizers and acids.
WCMP, using acidic chemistries and a hydrogen-peroxide-based oxidizer (Cabot W2000), forms stable
tungsten oxide particles in the process effluent. These particles can be captured in ceramic filters
along with the alumina abrasive used for polishing. After filtering, WCMP effluents can be diluted
and neutralized much like other chemicals used for etching in a wafer fab. Hydrogen peroxide can
be reacted away using activated carbon filters. Oxidation of tungsten makes WCMP process efflu-
ents less of a problem than Cu effluents.
Cu CMP effluents require more advanced techniques for management. Currently, Cu CMP effluents
are filtered using ceramic systems (US Filter Corporation, Kinetico Inc.) and post-processed. Ceramic

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