Materials Swagelok vFinal DR 18/12/08 12:22 Page 45
MATERIALS
45
Figure 2 (Valve
Manifolds)
Valve manifolds
enable efficient and
effective heat control
and retention. In
each manifold,
multiple actuators
are attached to a
single, solid block of
stainless steel
containing
interconnected
valve bodies for the
numerous valves
timed, precisely quantified doses. Figure 1
represents an ‘engineered to order’ ALD valve that
meets these criteria. Carrier gas enters through
Port A and exits through Port B. The carrier gas
is always ‘on’ when the process is running. The High temperature control and
liquid precursor enters through Port C, which is a monoblocks
small, precise orifice that delivers minimum To meet temperature control requirements, ALD
chemical volume. valves employ heater cartridges which are placed
For vaporisation to occur, both the valve and in the valve body. Finite element analysis (FEA)
the liquid precursor are heated to the optimum simulates the temperature effect, enabling valve
temperature so when the liquid is injected into the manufacturers to customise placement according
valve, it flashes across the seat into a gaseous to the tool manufacturerís particular needs.
state. Instantly, it mixes with the carrier gas, and When multiple valves and ports are used, a
is delivered to the chamber along with the flow of manifold is recommended to retain and control
carrier gas. When Port C closes milliseconds later, heat. Figure 2 shows two manifold options. In
the flow of liquid stops, but the carrier gas each, multiple actuators are attached to a single,
continues to flow, performing a purge function. solid block of stainless steel containing the body
Other systems might require multiple valves to for numerous valves. A block of stainless steel can
perform precursor and purge gas functions. be heated, maintained, and monitored at high
The mark of success for a system of this kind is temperature with accuracy and efficiency. By
repeatability. The valve must deliver precisely the contrast, a conventional assemblage of many
right amount of chemistry to the chamber distinct valves and multiple connections, heated up
consistently in each cycle. A compact unit with a with heater tape and divided into multiple heat
small space for chemical mixing minimises zones, is difficult to heat evenly.
variables and enables consistent chemical A principal challenge regarding temperature is
concentrations and consistent heat control. consistency along the entire flow path; another is
For vaporisation to occur, both the valve and the liquid precursor are
heated to the optimum temperature so when the liquid is injected
into the valve, it flashes across the seat into a gaseous state
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