Patent ID: 8628678

Claim:
A method for in-line measurement of an active KOH concentration in a KOH etching process in which silicon hydroxide is produced by a reduction reaction according to the formula: 2K + (aq.)+2OH − (aq.)+2H 2 O+Si→2K + (aq.)+H 2 SiO 4 2− (aq.)+2H 2 (g), the method comprising: measuring a total concentration of KOH and K 2 H 2 SiO 4 in an etch bath using a refractometer, estimating a concentration of K 2 H 2 SiO 4 in the etch bath, and determining the active KOH concentration in the etch bath using the measured total concentration of KOH and K 2 H 2 SiO 4 and the estimated K 2 H 2 SiO 4 concentration, wherein the concentration of K 2 H 2 SiO 4 is estimated after processing about ten or less batches of silicon and estimating the concentration of K 2 H 2 SiO 4 comprises performing a balance calculation using an estimated amount of Si dissolved into the bath from each batch.