Strong etching formulation (time and rate) for PADC with deep depth bulk etch rate study

Aqueous NaOH with ethanol (strong) etchant is widely used. It shortens etching time effectively compared to normal etching conditions (6.25N NaOH at 70 °C). Two equations have been proposed to calculate the etching time with NaOH molarity and ethanol volume. Another two empirical equations were introduced for estimating the bulk etch rates of PADC etched in strong etchant. Up to now, there were no such equations available in the literature that can predict etching time and $V_b$ of PADC with etchant molarity and ethanol volumes. The proposed equations were compared to fundamental $V_b$ models stemming from literature. Fast etching enables the follow-up of bulk etch rate variation versus depth in the detector material up to $\approx$ $80\mu$ m. In agreement with previous studies, an equation is given which allows such variations to be expressed under the form of a reciprocal bulk etch rate normalized to depth (i.e., removed layer).