[7] The use of cryopumps became common in semiconductor manufacturing worldwide, with expansions such as a cryogenics company founded jointly by Helix and ULVAC (jp:アルバック) in 1981.
Cryopumps are commonly cooled by compressed helium, though they may also use dry ice, liquid nitrogen, or stand-alone versions may include a built-in cryocooler.
Baffles are often attached to the cold head to expand the surface area available for condensation, but these also increase the radiative heat uptake of the cryopump.
The cryopump operates on the principle that gases can be condensed and held at extremely low vapor pressures, achieving high speeds and throughputs.
Even at this temperature, the lighter gases helium and hydrogen have very low trapping efficiency and are the predominant molecules in ultra-high vacuum systems.
Cryopumps are often combined with sorption pumps by coating the cold head with highly adsorbing materials such as activated charcoal or a zeolite.
As the sorbent saturates, the effectiveness of a sorption pump decreases, but can be recharged by heating the zeolite material (preferably under conditions of low pressure) to outgas it.
Water vapor is the hardest natural element to remove from vacuum chamber walls upon exposure to the atmosphere due to monolayer formation and hydrogen bonding.