An ultra-pure ozone water comprising an increased amount of an organic
carbon capable of suppressing the reduction of the half-life period of
ozone; and a method for producing the ultra-pure ozone water which
comprises adding an organic solvent containing the above organic carbon
to an ultra-pure ozone water containing a trace amount of the organic
carbon. The above ultra-pure ozone water exhibits an increased half-life
period of ozone, and thus, when used in cleaning a semiconductor
substrate, allows the cleaning with an ozone water having an enhanced
content of ozone, which results in exhibiting an enhanced cleaning
capability and cleaning efficiency for an organic impurities, metallic
impurities and the like adhered to the substrate, due to enhanced
oxidizing action of ozone.