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Source: SEMICONDUCTOR MANUFACTURING HANDBOOK

CHAPTER 17

CHEMICAL MECHANICAL
POLISHING

Timothy S. Dyer
Carpenter Advanced Ceramics
Auburn, California

17.1 INTRODUCTION TO CMP

Chemical mechanical polishing or planarization (CMP) has enabled the production of advanced
semiconductor devices by producing a globally planar wafer surface. The optical depth-of-focus
issues of photolithography drives the near-atomic-level flatness achieved by CMP, which is a highly
sophisticated process. Photolithography requires a flat surface to image dense, multilayer integrated
circuits. In general, the smaller the device features, the flatter the substrate must be. At the current
device technology node, global wafer planarization and CMP are necessary for building reliable
next-generation multilevel interconnects.

17.1.1 Advantages of CMP
CMP offers many advantages over standard reactive ion etching (RIE) processes. For one, RIE
processes cannot readily etch copper. CMP does a very good job removing copper for the semicon-
ductor wafer surface while at the same time producing a surface that is both very smooth and flat.
CMP is mainly used for silicon dioxide, polysilicon, copper, low-k dielectrics, and tungsten removal
and planarization. CMP is an elegant process and can be completed in a semiclean environment in the
wafer fab. CMP tools tend to be massive and large. Though CMP processes require chemicals, they
do not require the use of dangerous pyrophoric or highly toxic gases like most RIE or chemical vapor
deposition (CVD) systems.

17.1.2 The Science of CMP
CMP is a straightforward process to understand. A thin film on a wafer surface is abraded by a simul-
taneously using a chemically active slurry, moving polishing pad, and an applied polishing down
force (See Fig. 17.1). Fundamentally, its roots lie in the science of friction and wear called tribology.
In brief, the science of tribology characterizes both friction and wear of substances. Some folks
believe that high friction during polishing suggest high-stock material removal rates, however, this
is generally not true. Polishing friction is system related and therefore is a unique behavior of the
materials, surfaces, linear velocity, and chemistry involved in the polishing process. Material
removal rates are generally proportional to the work done to the film being polished.

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