AB-344
Automated analysis of etch acid mixtures for silicon substrates with thermometric titration
Summary
This Application Bulletin describes the automated determination of mixtures of HNO3, HF, and H2SiF6 in the range of approximately 200–600 g/L HNO3, 50–160 g/L HF, and 0–185 g/L H2SiF6 using thermometric titration. Etch acid mixtures containing HNO3, HF and H2SiF6 from the etching of silicon substrates can be analyzed in a sequence of two determinations. The first determination involves a direct titration with standard c(NaOH) = 2 mol/L, followed by a back titration with c(HCl) = 2 mol/L. This determination yields the H2SiF6 content plus a value for the combined (HNO3 + HF) contents. The second determination consists of a titration with c(Al3+) = 0.5 mol/L to determine the HF content. The HNO3 content can then be calculated from the results.
For freshly prepared mixtures of HNO3 and HF containing no H2SiF6, a linked two-titration sequence can be used. In the first titration, the combined HNO3 + HF content is determined with c(NaOH) = 2 mol/L. This titration is automatically stopped, and a second titration with c(Al3+) = 0.5 mol/L is started to determine the HF content. The HNO3 content can then be calculated from the results.