Single beam determination of porosity and etch rate in situ during etching of porous silicon

Journal of Applied Physics

2016

There are a few methodologies to monitoring the Porous Silicon (PS) formation in-situ. One of these methodologies is photoacoustic. Previous works that reported the use of photoacoustic to study the PS formation do not provide the physical explanation of the origin of the signal. In this paper, a physical explanation is provided of the origin of the photoacoustic signal during the PS etching. The incident modulated radiation and changes in the reflectance are taken as thermal sources. In this paper, a useful methodology is proposed to determine the etching rate, porosity, and refractive index of a PS film by the determination of the sample thickness, using SEM images. This method was developed by carrying out two different experiments using the same anodization conditions. The first experiment consisted of the growth of samples with different etching times to prove the periodicity of the photoacoustic signal and the second considered the growth samples using three different wavelengths that are correlated with the period of the photoacoustic signal. The last experiment showed that the period of the photoacoustic signal is proportional to the laser wavelength.

Section: Introductionmentioning

confidence: 99%

“…Profilometry has been used to determine interface roughness, and gravimetry to determine the porosity. 1 These techniques are contact, destructive, and are not able to give information about physic properties at the same time that the PS is forming.…”

Section: Introductionmentioning

confidence: 99%

In situ photoacoustic characterization for porous silicon growing: Detection principles

Journal of Applied Physics

2016

“…It was found that the etching velocity as well as the porosity have time dependence. On the other hand, Foss et al 8 used the same methodology to determine the porosity, the thickness, and the roughness of the PS film thru a back detection.…”

Section: Introductionmentioning

confidence: 99%

Modeling the photoacoustic signal during the porous silicon formation

Journal of Applied Physics

2017

Within this work, the kinetics of the growing stage of porous silicon (PS) during the etching process was studied using the photoacoustic technique. A p-type Si with low resistivity was used as a substrate. An extension of Rosencwaig and Gersho model is proposed in order to analyze the temporary changes that take place in the amplitude of the photoacoustic signal during the PS growth. The solution of the heat equation takes into account the modulated laser beam, the changes in the reflectance of the PS-backing heterostructure, the electrochemical reaction, and the Joule effect as thermal sources. The model includes the time-dependence of the sample thickness during the electrochemical etching of PS. The changes in the reflectance are identified as the laser reflections in the internal layers of the system. The reflectance is modeled by an additional sinusoidal-monochromatic light source and its modulated frequency is related to the velocity of the PS growth. The chemical reaction and the DC components of the heat sources are taken as an average value from the experimental data. The theoretical results are in agreement with the experimental data and hence provided a method to determine variables of the PS growth, such as the etching velocity and the thickness of the porous layer during the growing process.

“…This means, that during the PSi formation, it is possible to follow the changes in the thickness, roughness, and porosity by using light interferometry because the optical path changes continuously and multiple interfaces where the light can be reflected appear. This methodology and the mathematical model were reported in [12][13][14][15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

“…The main techniques reported to study the in situ formation of PSi by electrochemical etching in hydrofluoric acid(HF) media are: in situ Fourier transform infrared spectrometry (FTIR) [10,11], optical interferometry [12][13][14][15][16][17] optical scattering [19,20], and photoacoustics [21][22][23][24][25].…”

Section: Introductionmentioning

confidence: 99%

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

2018

Open Material Sciences

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, noncontact, 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 λ 0 /4 to ∼ 1/α 0 , where α 0 is the optical absorption coefficient at λ 0 . Also, these techniques can be implemented as feedback control on the etching processes for fabrication of PSi.