System for diluting ultrapure chemicals which is intended for the microelectronics industry

System for diluting an ultrapure concentrated chemical comprising

• (i) a first tank which contains said chemical in concentrated form having a predetermined purity P,
• (ii) a supply of ultrapure water of purity at least equal to P,
• (iii) a second tank for mixing the concentrated chemical with the ultrapure water to obtain a solution of diluted chemical whose purity is at least equal to P,
• (iv) means for adjusting the titre of the solution of diluted chemical to a desired final concentration comprising
• (a) means for measuring the titre of the dilute solution after mixing a predetermined quantity of ultrapure water with concentrated chemical of purity P so as to obtain a mixture with a concentration of chemical which is greater than the desired final concentration of the diluted chemical,
• (b) means for adding an additional quantity of ultrapure water to the mixture to obtain a second further diluted mixture, this additional quantity being at most equal to a theoretical quantity necessary for obtaining the desired titre, and
• (c) an ejector stirrer having an outer tube of predetermined diameter and an inner tube disposed in said outer tube, wherein said inner tube extends to a predetermined depth h beyond the outer tube in said second further diluted mixture, and further stirs the second mixture for a time such that the diluted chemical is recirculated on itself at least approximately three times so as to ensure that the diluted chemical is well homogenized and that the titre is substantially constant over the entire volume of the diluted chemical, and
• (d) means for checking the titre of the solution of diluted chemical;
• and
• (v) a third tank for storing the chemical.