Apparatus and method for controlling resistivity of ultra pure water

An apparatus for controlling resistivity of ultra pure water, comprising:

• a mixed gas supply;
• a membrane module having a gas permeable membrane, the membrane module being capable of supplying carbon dioxide or ammonia to untreated ultra pure water so that the concentration of carbon dioxide or ammonia in the ultra pure water becomes equal to or more than 90% of the equilibrium concentration within an expected fluctuation range of the flow rate of the untreated ultra pure water, and
• a unit which produces ultra pure water in which carbon dioxide gas or ammonia has been dissolved in a sufficient amount to obtain a desired resistivity at any flow rate of the ultra pure water supplied, by contacting the ultra pure water with 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, via the gas permeable membrane.

A method for controlling resistivity of ultra pure water, comprising the steps of:

• supplying a mixed gas, 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, to a flow of ultra pure water via a gas permeable membrane;
• and
• producing resistivity-controlled ultra pure water by dissolving carbon dioxide or ammonia in the ultra pure water to a concentration equal to or more than 90% of the equilibrium concentration which is determined by the concentration of carbon dioxide or ammonia in the mixed gas, the partial pressure of carbon dioxide or ammonia in the mixed gas, and the temperature of the ultra pure water.

A method for controlling resistivity of ultra pure water, comprising the step of:

• contacting ultra pure water with a mixed gas, 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, via a membrane module having a gas permeable membrane, the membrane module being capable of supplying carbon dioxide or ammonia to the ultra pure water so that the concentration of carbon dioxide or ammonia in the ultra pure water becomes equal to or more than 90% of the equilibrium concentration within an expected fluctuation range of the flow rate of the untreated ultra pure water, whereby resistivity-controlled ultra pure water is produced in which carbon dioxide gas or ammonia has been dissolved in a sufficient amount to obtain a desired resistivity at any flow rate of the ultra pure water supplied.