Pores growth control by in-situ FFT impedance spectroscopy

Fast Fourier transform impedance electrochemical spectroscopy (FFT EIS) and photoelectrochemical impedance spectroscopy (FFT-PEIS) have been used for the first time to characterize in-situ the dynamics of macropore growth in n-type Si under backside illumination. In the case of PEIS the illumination intensity was modulated and the response of the etching current (at constant voltage) was measured, thus an impedance-like transfer function was obtained. A theoretical model taking into account the minority carrier diffusion in the semiconductor and the ion diffusion in the electrolyte successfully fit the impedance data from both EIS and PEIS. From the fit quantitative data, for example the pore depth or the diffusion length of the minority carriers, could be calculated in-situ and in real time during the pore growth. The new technique can be used as feedback for active control in automated pore etching.