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Frequently Asked Questions
- Does the DryScrub®Plasma
Trap System interfere with the existing vacuum system?
NO. The DryScrub® Plasma Trap is
virtually transparent to any existing vacuum system. The current design
of 2DH electrode gives conductance >50,000 liter/sec in the viscosity
flow regime and >5,000 liter/sec in the transition regime. DryScrub® Systems have been successfully installed in
many LPCVD/PECVD including: AMAT PE5000, ASM, Axtron, Kokusai (KE),
Novellus, SVG, TEL, and other systems.
- What other applications can the DryScrub® Plasma Trap System be used for?
DryScrub® Plasma Trap utilizes the patented RF
capacitance coupled plasma technology to treat semiconductor processing
exhaust gases. The applicable processes include LPCVD/PECVD, silicon and
metal nitrides and oxides, MOCVD and ALD metals, Ion Implantation,
Plasma Etching and Chamber-clean PFC abatements. For more information,
please call us.
- What can the DryScrub® Plasma Trap System do to abate etching and chamber-clean PFC
gases?
For etching gases (CF4, C2F6, etc),
DryScrub® systems provide adequate RF energy to decompose
the unpolarized and stable PFC gas molecules into polarized and active
radicals/molecules under vacuum without added gases. The F atoms etch
the as deposited silicon nitride and oxide to form SiF4 and clean up the
electrode. The polarized components and SiF4 are soluble in
water/chemical and can be scrubbed by any central wet chemical scrubber.
It reduces the PFC emission and protects the environment while recycle
the electrode for next deposition process. It eliminates powder
formation during deposition cycle and abates PFC during the etch clean
cycle.
For CVD Chamber-clean effluents, the DryScrub® system can do several things to improve the
overall performance. Firstly, it can strip the solid components of
hydride processing gases from exhausts. This will reduce the flow of
particles to your downstream particle filters and membrane, which
facilitate downstream PFC capture and recycle processes. Secondly, the
films on the DryScrub®
electrodes, which have almost identical chemical components to wafer
films, can react with un-reacted Chamber-clean PFC gases to increase the
reaction efficiency of PFC gases. This application is used to reduce the
PFC emission. Under such application, the electrode has a much longer
life time. Various functions can be achieved by programming the RF power
supply differently.
- Why the DryScrub®
Plasma Trap System can reduce the particle counts on wafers in CVD
processing?
There are many sources of particles in a CVD process. From the gas
source line, the wafer handling, the chamber deposited film peeling off
and from the uncontrollable but most important, back diffusion of
particles generated in downstream gases. The reactive process gases are
energized after the process tool. These reactive nano-metric size
molecules back diffuse into the process chamber. They react with other
particles and coagulate together, larger than 100 nm size particles are
formed within short reaction times. The coagulating process is amplified
by the seeding of the already existing molecular clusters and sub-micron
particles that have been generated by the pump. For condensable gases,
such as TEOS and NH4Cl, coagulation is further enhanced by the
nucleation process, due to the large temperature drop at the foreline.
With an installed DryScrub® Plasma
Trap between the CVD chamber/furnace and the pump, the charged plasma
strips solid components and deposits them in dense films, >99.5%
elimination of solid bearing gases by deposition reduces particle
formation. At the same time, the charged plasma inside the capacitor
like electrode also functions as a trapper, it's like an electrostatic
precipitator for particles flowing from upstream and downstream.
DryScrub® improves the wafer yield and reduces the cost
of ownership (COO).
- What is the advantage of choosing DryScrub® Technology to abate exhaust gases, compared
to conventional burn box, CDO, GRC, etc.?
Assuming Burn Box, CDO and other technologies can abate the exhaust
gases with the same efficiency as DryScrub® System, then, the main advantage of using
DryScrub® is that it benefits pump and other downstream
facilities. The DryScrub® is
installed before the pump. >99.5% solid components of hydride gases
are stripped by the DryScrub®
System, leaving neutral gases to pass through the pump and downstream facilities.
This will prevent pump failure, APC valve and vacuum line clogging
issues. It reduces operation cost and increase process up-time.
Open flame technology burns exhaust gases. It requires additional fuel
such as H2 or natural gases. Since exhaust gases have
been highly diluted, for example below 2% for a hydride gas such as
silane, most of the burning is of the natural gases, which heats air and
leads to the formation of toxic NOx. In addition, solids are expected to
deposit, by gas phase nucleation, near the nozzle and downstream. The
foam deposition requires the cleanup of the nozzle virtually daily when
on a production line, an extensive maintenance and downtime. Pyrophoric
gases such as SiH4 are trapped in the foams, which can ignite,
the cost of fuel and safety issues have to be considered.
Controlled Decomposition and Oxidation (CDO) technology uses heating
elements to supply thermal energy for the exhaust gas reaction and
decomposition. The addition of N2 and O2 (air) dilutes and increases the overall
volume of exhaust gas. Under atmospheric pressure, the exhaust gases
nucleate and form foam type byproducts on the hot surface. Once a loose
foam type layer is formed, it reduces the rate of heat transfer to the
bulk exhaust gases, and lowers the exhaust gas reaction rates
exponentially. Therefore, the scrubber efficiency decays dramatically
with time once a loose foam type layer is formed.
The gas reactor column (GRC) technology uses solid inorganic materials
to react exhaust gases on the solid granular surfaces. When new,
inorganic solids have many fresh sites to allow gas molecules to be
adsorbed and reacted effectively. However, once the reaction products
cover the solid surface as an oxide or nitride sheath, the reaction rate
reduces dramatically, toxic gases must diffuse and react with the inner
core of the inorganic materials. Please draw the parallel that very thin
oxide or nitride layers are purposely deposited on wafers as barrier
layers to block the penetration of gas and moisture. The nitride or
oxide by-products block the diffusion of exhaust gasses and stops the
reaction. When new the GRC can be effective, but as the surface gets
clogged most of the exhaust gas will simply pass by and efficiency drops
dramatically. The GRC cartridge itself contains a large quantity of
inorganic solid. After the gas treatment, GRC generates a large quantity
of waste in volume. The cost for solid waste disposal is high. Unlike
the DryScrub® System which uses one electrode for any type
of process gas, GRC uses different types of cartridges for various
processing gases.
- What is the DryScrub® preventative maintenance (PM) procedure?
The PM procedure of DryScrub® is
simple. Only the electrode needs to be replaced. This can be done within
30 minutes.
- What is the DryScrub® preventative maintenance frequency?
The PM frequency depends on the hydride gas flow rate and processing
time. Normally, an electrode can last for a couple of months. Please
refer to the Technical Notes. This expression is given to calculate how
many runs or the total deposited film thickness the electrode can handle
before replacing. If you have any difficulty to figure it out, please
call ETC. One of our engineers can help you out within a few minutes.
- What waste gases leave the DryScrub® System?
Please refer to the following note "Summary Table of DryScrub®
Collection Capacity" for the components of waste gases leaving the
DryScrub®. If your process is not listed in the Summary
Table of DryScrub® Collection Capacity, please call ETC for help!
- What are the materials collected by the
electrode and how should I dispose of the used DryScrub® electrode?
The solid materials in the electrode are virtually identical to those on
wafer films. The Summary Table of DryScrub® Collection Capacity shows the waste materials
for various LPCVD/PECVD processes. Since the solids in the electrode is
more or less non-toxic, they can be disposed with other solid wastes.
Please check with ETC and your safety team for more details.
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