In situ and real-time optical study of passive chemical etching of porous silicon and its impact on the fabrication of thin layers and multilayers

In this work, we report on the development and application of a simple reflectivity technique for real-time monitoring of the fabrication of porous-silicon multilayers. The technique allows for high-resolution quantification of the effective optical thickness of the layers during the fabrication process, enabling calibration of attack rates and detection of changes in porosity. Our experiments revealed that the porosity of the layers increases during the attack, indicating incomplete passivation of the pores. By studying thin porous-silicon layers in the absence of applied current, we developed a three-layer model to understand passive chemical etching. Furthermore, our study allowed discrimination between the two mechanisms responsible for the reduction of effective optical thickness with time, with changes in porosity being the dominant one. The technique has the potential to enable real-time control of multilayer fabrication, offering flexibility in controlling environmental conditions and silicon wafer conduction properties. Our results contribute to the understanding of multilayer fabrication and reflectivity-based process monitoring.

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