Introduction
The cycle time for an industrial high vacuum batch evaporation or sputter plant is inverse proportional to the installed pumping speed of vacuum
pumps. For half a cycle time, twice the pumping power is required. Traditionally, diffusion pumps are required for a high vacuum process. Because the efficiency factor (Ho-factor) of these pumps is lower
than 50 % for a given geometry, it is not possible to indefinitely increase the installed pumping speed, even if someone is willing to pay the high operation costs of increasing the speed.
A quasi-ideal
solution would be to use a low-temperature cryopanel. The by-product gas produced with a high vacuum plant is not air, but over 90 % water vapor. With a cryopanel the vapor condenses on the panel, forming
ice crystals with which the partial pressure of the ice reaches the ultra-high vacuum range. The efficiency of the cryopanel is approximately 100 % because all of the water vapor that hits the panel
condenses to ice. The intrinsic pumping speed of 1 m² on the cold surface rises over 140, 000 l/s.
When a cryopump is combined with the Sputter Plant the capability is increased, as the pumping
speed of the cryopump is mot affected by the higher pressure of the sputter process. Additionally, the cryopump/sputter plant combination does not pump expensive gasses like argon. When compared with
conventional pumps, which work properly only in the molecular range and also require expensive gasses like argon, the cryopump/sputter plant combination offers a more efficient process at a better
price/performance advantage.
The question is now, how to produce a low temperature panel with the minimal cost? A practical solution is to use a refrigerator machine, like a low temperature "Frigidaire".
But this type of machine requires expensive investments, the compressor has a limited lifetime, and while the running costs for the electricity and cooling water are cheaper than for an equivalent diffusion
pump, they are not opzimized.
A better solution is to use a liquid nitrogen cooled panel. The cost for liquid nitrogen is low (10 to 20 cents/liter), as liquid nitrogen is a waste product produced through
oxygen when using autogenous soldering. For 10,000 l/s pumping speed, the consumption of liquid nitrogen is approximately 1 liter/hour- a price without competition!
Other advantages of Liquid Nitrogen
Cryopumps include: lower investment costs, quasi-indefinite life time of the pump (no motor, no moving parts), no current, no water all leading to relatively no maintenance costs. Industrial plants can be
fully automated. The pump must be filled once a day (generally from a larger storage tank that is refilled once a month from the LN supplier). Competitors may argue that the handling of LN is not practical,
is invalid.
Regeneration of the pump, i.e. removing of the ice layer, is necessary after 4000 cycles, or approximately 1000 hours of continuous operation. This is much lower than most industrial pumps,
which generally require weekly maintenance. The regeneration of the cryopump is done automatically after warm-up. Human intervention is not required.
The use of a LN cooled surface is an old solution in
vacuum technology known as a "Meißner trap". FPT has improved the design of the pumps; the standard capacity of the pumps has been increased to over a day or more. Additionally, the consumption of LN has
been reduced to the theoretical minimum. This has been achieved through the use of a rest enthalpy of the cold nitrogen vapor. Through a heat exchanger, the cold nitrogen vapor cools a heat shield, which
surrounds the inactive surface of the reservoir. Liquid Nitrogen - high vacuum pumps
Standard flanges ISO DN 250 up to DN 1000
Pumping speed 4000 l/s up to 100000 l/s |
