Understanding and Controlling Pore Etching in Semiconductors

Abstract

The paper first compares pore formation in semiconductors, and then turns to some common features found in all semiconductors. In particular, the appearance of some kind of self- organization, expressed as pattern formation in time (e.g. self- induced current oscillations) or in space (e.g. pore crystal formation), will be discussed. A stochastic model of the electrode dissolution via oxidation, implemented in a Monte- Carlo algorithm, can reproduce some of these phenomena quite closely, and the paper will give some new results. For a deeper understanding of pore etching as well as for some control of etching parameters over etching time, it is necessary to have some in-situ measurements that contain data about what is going on at the pore tips deep inside the sample. It will be shown that Fast-Fourier Transform (FFT) impedance spectroscopy (IS) is principally suited to the task. The method gains even more power if photo impedance , i.e. modulation of the backside or frontside illumination and monitoring the current response, is used in conjunction with suitable theoretical models. Extending FFTIS to other semiconductor like InP or to basic processes like anodic oxidation provides new insights; this will be demonstrated for the case of anodic oxidation in a range of organic electrolytes often used for pore etching in p-type semiconductors.