| http://www.w3.org/ns/prov#value | - Normally, while etchant gases, including gaseous hydrogen fluoride, water vapor and a diluent such as nitrogen, are in the etch chamber 12, nitrogenwill be flowed upwardly through the shaft 27 and passageway 28 and through the check valve 35 at a slow rate of speed so that there is no possibilityof the etchant gas flowing downwardly through the passageway 28 and into the source of vacuum.
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