Optical interferometry and photoacoustics as in-situ techniques to characterize the porous silicon formation: a review

Abstract Porous Silicon (PSi) is a groundbreaking material because its physicochemical properties can be customized through its porosity. This means that monitoring and control of the growing parameters allows the fabrication of PSi-based systems with controlled properties. Interferometry and photoacoustics are non -invasive, non - contact, real-time (in-situ) techniques used to characterize the phenomena that takes place during the formation of PSi. This work presents the mathematical and experimental aspects related to the implementation of the techniques mentioned above, which are meant to characterize the PSi growth in fluoride-based electrolyte media. These methods can determine macroscopic parameters of PSi such as thickness, porosity profile trough effective medium approximation (EMA), refractive index, etching rate, and RMS roughness under 100 nm. The monitoring ability of these techniques is strongly dependent on the wavelength of radiation used. However, it is possible to monitor thickness from λ0/4 to ∼ 1/ α0, where α0 is the optical absorption coefficient at λ0. Also, these techniques can be implemented as feedback control on the etching processes for fabrication of PSi.