Abstract
Chemicals and materials are used in every processing step in the fabrication
of silicon and gallium arsenide integrated circuits. Technological advances in
Si and GaAs ICs have resulted in more stringent requirements in the purity and
quality of processing chemicals and materials for cleaning, etching, and
deposition. As linewidths decrease, the level and size of contaminants in both
chemicals and the manufacturing cleanroom become increasingly important as it
directly impacts device yield. Each new generation of IC processing requires
higher levels of purity.
Front-end-of-line (FEOL) and back-end-of-line (BEOL) wet chemical cleaning
processes are critical to the fabrication of semiconductor devices. As
linewidths continue to shrink, maximizing the purity of chemicals used in wet
cleans is a prerequisite for maintaining and improving chip yield. The
incoming and in-process purity of chemicals used in wet cleaning greatly
impacts the surface contamination of wafers. While incoming ultrapure
chemicals have reduced ion levels, exposure to metallics has persisted during
wet processing.
One way of effectively minimizing ionic contamination is to continuously
purify the chemicals in use. In this approach, the metallic ions are removed
by binding them to the complexing agents immobilized on membrane filters that
can be plumbed in-line in the wet tools.
During the manufacture of microelectronic devices, silicon wafers are exposed
to high-purity water more frequently than any other liquid chemicals, and can
require >1100 gal of ultrapure rinse water to process a 200 mm wafer.
However, it is difficult to maintain high purity below 1 ppt out of the
central system during the distribution to points of use for wafer surface
cleaning. The process of distributing high-purity DI water often introduces
particles and trace ionic contamination that can leach out from the plumbing
components and process equipment. The ITRS 2001 guidelines call for a total
metal contamination level on the wafer surface of <7 X 109 atoms/cm2 for
130 nm devices.
Purification and filtration technologies have been developed to achieve the
stringent purity levels required of liquid chemicals in semiconductor
manufacturing. Although shrinking geometries continue to drive this
innovation, other process-related needs that will provide the impetus for
purification are:
- Use of dilute chemistry requiring more stringent ionic specs to prevent
metal deposition on wafers.
- More focus on waste DI reclaim/recycle applications for future lithography
resource conservation.
- To decrease fab ultrapure water use from 6-8 gal/in.2 in 2001 to 4-6
gal/in.2 in 2005, and 3-5 gal/in.2 beyond 2008.
The BEOL wet cleaning process has become increasingly important as the number
of metal levels has increased with the shrinking feature sizes of the newer
ICs. In fact, BEOL constitute up to 50% of all wet cleaning steps. BEOL
cleaning steps begin at the end of FEOL after a metal layer is deposited on
the wafer. The presence of a metal layer precludes the use of aggressive
cleaning steps used in FEOL, as the metal layers would be attacked. The BEOL
cleaning uses less reactive solvents (e.g. NMP - N-Methyl-2-Pyrrolidinone)
for photoresist stripping, which are expensive to use and dispose of.
For residue stripping, after an ashing process, many less aggressive
semi-aqueous cleaning chemistries have been introduced. To lower the high cost
of cleaning and to reduce defect density, it has become critical to clean up
and extend the life of chemical bath by point-of-use purification with
optimized filtration.
Photoresist stripping involves removal of bulk photoresist; the chemicals used
are primarily organic in nature, slightly to highly basic. Residue stripping
removes particulate, organic and inorganic contamination after the photoresist
has been removed by plasma ashing or after liquid photoresist stripping. The
residue stripping chemicals are semiaqueous or aqueous-a very diverse mixtures
of solvents, amines, and corrosion inhibitors.
Standard hydroxyl amine based chemistries have shown good polymer
removal/cleaning performance, but require high temperatures and 15-45 min.
process times. The new semi-aqueous fluoride based cleaning chemistries can be
used at low or room temperature for wet benches, spray tools and the single
wafer tools.
Ultrapure DI water rinsing process following the chemical cleaning step is
very critical from the metal corrosion standpoint. Point-of-use
purifier/filter devices for the removal of low level metal and particulate
contamination from ultrapure water, organic solvents, and other chemicals used
in microelectronics.
This report is offered for the purpose of assisting a user in evaluating the
spectrum of products, packaging, and dispensing systems available for his use.
It also suggests criteria for selecting a vendor as well as a chemical
delivery and dispensing system that will serve his specific requirements.
The report also gives insights to suppliers for future user needs and should
assist them in long-range planning, new product development and product
improvement.
This report addresses the strategic issues impacting both the user and
supplier of chemicals and materials and is written for:
- Chemical and material suppliers to the semiconductor industry
- Executive personnel of semiconductor manufacturing facilities
- Buyers of chemicals and materials for the semiconductor industry
- Strategic planners of semiconductor facilities
- Product planners of chemicals and materials to the semiconductor industry
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