Patent ID: 6884359

Claim:
An apparatus for controlling resistivity of ultra pure water, comprising: a mixed gas supply; a housing to house a gas permeable membrane, the gas permeable membrane dividing the interior of the housing into an ultra pure water path and a mixed gas path wherein a mixed gas from the mixed gas supply, selected from the group consisting of a mixed gas comprising carbon dioxide and a gas having a lower resistivity controlling ability than carbon dioxide and a mixed gas comprising ammonia and a gas having a lower resistivity controlling ability than ammonia, passes the mixed gas path, and the housing has an opening for supplying the mixed gas through which the mixed gas path communicates with the exterior of the housing; an inlet for untreated ultra pure water which communicates with the ultra pure water path; and an outlet for resistivity-controlled ultra pure water which communicates with the ultra pure water path, wherein the gas permeable membrane is capable of supplying carbon dioxide or ammonia to the untreated ultra pure water which passes through the ultra pure water path at a concentration equal to or more than 90% of the equilibrium concentration.