Metal Contaminant Reductions
Entegris, Inc. Semiconductor device yields have long been impacted by device contamination. As process nodes continue to shrink from 10 nm to 7 nm and soon to 5 nm — pushing CMOS to its
Where does metal contamination originate?
very limits — the sensitivity to metal contamination
during manufacturing processes has increased sig-
nificantly. This article describes the primary causes
of metal contamination in gas streams and ways to
address the problem through the use of specially-de-
signed gas delivery systems.
Possible root causes of semiconductor device contamination in the front- and back-end-of-line processes include sensitivity to different process steps
and cross-contamination induced by chemicals,
ultrapure water and gases. The process environment,
which included the tools, network for gas/chemical
distribution, and boxes for wafer handling and transportation, contribute to the problem.
Contaminants from the metallic components of
process tools, plumbing and tubing play a role in
metals contamination generation. Among the most
common metallic contaminants are the transition
metal constituents of 316L stainless steel — chromium (Cr), iron (Fe), manganese (Mn), molybdenum
(Mo), and nickel (Ni) — as well as main group metals including sodium (Na), calcium (Ca), and aluminum (Al). Depending on the metal, it can degrade
CMOS gate stacks, reduce carrier lifetime and more.
There are two main factors that contribute to
metal impurities on a wafer due to the process envi-
ronment itself: 1) metal contamination inherent to
the gas supply; and 2) corrosion of metal surfaces
induced by gases from the gas system itself due to
the gases that are required by semiconductor manu-
Not all processes requiring a gas supply use corrosive gases. Those that do, however, can impact
the entire gas supply network. Dry etch processes,
including ion beam etching, plasma etching, and
reactive ion etching use corrosive gases that include
arsenic pentafluoride, (AsF5), boron trichloride
(BCl3), chlorine (Cl2), hydrogen chloride (HCl),
silicon tetrafluoride (SiF4), and phosphine (PH3),
among others. Additional corrosives include dichlo-rosilane (SiH2Cl2, used in epitaxy) and chlorine
trifluoride (ClF3), which is used for cleaning various
semiconductor tool components.
In a high-volume manufacturing environment, it
is general practice to employ a main gas cabinet in
the sub-fab environment to store the bulk gas supply
for multiple process tools. The gas is delivered to
individual tools using a valve manifold box. Because
plasma etch and epitaxial tools can require the same
corrosive gases, both are typically supplied from the
same bulk source. This scenario subjects the entire
gas delivery system to corrosion and contributes to
the contamination of the gas supply itself.
Historically, the tolerance for metal contaminants in gas supplies was 1010 atoms/cm2. As devices
reach smaller nodes and sensitivity to contaminants increases, the industry has tightened purity
standards 100-fold to 108 atoms/cm2 in an effort to
reduce defect-causing contaminants found in process
gases. One way to meet this new standard is by using
gas purifiers designed to remove moisture, hydrocarbons, and volatile metals from corrosive gasses
Examining the semiconductor manufacturing processes.
Fig. 1. Filtration: A process
or device that contains a
porous element designed
suspended solid particles
from breaching the
in a gas stream.
All images: Entegris, Inc.