Apparatus and method for wet cleaning

An apparatus for cleaning semiconductor wafers using a dilute sulfuric peroxide hydrofluoric acid solution containing more than about 80% water by volume, the apparatus comprising:

• a process tank containing a cleaning solution comprising deionized water, sulfuric acid, and hydrogen peroxide;
• a monitoring system for performing over time a plurality of measurements of fluorine ion concentration in said cleaning solution to obtain a measured concentration level associated with each of said measurements;
• a source of hydrofluoric acid;
• a controller responsive to said measured concentration level, wherein said controller generates a first indicator when said measured concentration level is below an initial threshold, said controller further capable of generating a second indicator when said measured concentration level equals or exceeds said target fluorine ion concentration level, wherein said initial threshold is less than said target fluorine ion concentration level, and said controller further capable of generating a third indicator when said measured concentration level is below a third threshold, wherein said low threshold is greater than said initial threshold and less than said target fluorine ion concentration level;
• and
• a pumping device responsive to said controller to add a first amount of hydrofluoric acid to said cleaning solution from said source, said first amount of hydrofluoric acid sufficient to achieve a target fluorine ion concentration level and thereafter maintaining said fluorine ion concentration substantially at said target fluorine ion concentration level.