Determination of Stress in Porous Silicon by Micro-Raman Spectroscopy

Abstract

We have studied the stress in porous silicon films as a function of depth and porosity using micro-Raman spectroscopy. Raman spectra were measured at different points along a cross section cleaved normal to the layer planes. Each spectrum was fitted using the phonon confinement model with the bulk phonon wavenumber as a free parameter. From the variation of this parameter we get the stress using the known dependence of phonon frequency on stress for bulk silicon. We observe a compressive stress at the interface with the substrate due to the lattice mismatch between porous and bulk silicon. The maximum value of the stress increases with porosity. The results obtained by Raman micro-spectroscopy agree well with the lattice mismatch measured by X-ray diffraction reported in the literature.

Investigation of nanostructured porous silicon by Raman spectroscopy and atomic force microscopy

“…Disorder or finite size effects may result in a relaxation of the momentum conservation rule, leading to a downshift and an asymmetric broadening of the first order Raman peak. Therefore, the first order Raman band of porous silicon is calculated by the sum of two components: a band given by the phonon confinement model and a Gaussian distribution to account for amorphous silicon [8]. In this way, the intensity of the Raman signal is given by…”

X-ray investigation of nanostructured stain-etched porous silicon

“…[9][10][11][12] Raman-scattering spectroscopy, together with the phonon confinement model, has been demonstrated as a powerful technique to investigate PS structure. [13][14][15] Furthermore, highresolution x-ray techniques have been applied to obtain information about the peculiar structure and strain of porous Si. [16][17][18][19] However, the determination of size and shape distribution of crystallites in PS layers is still a subject of intense interest.…”

Micro and Nano Structure of Electrochemically Etched Silicon Epitaxial Wafers

“…At the same time the peak position of the TO bands of samples S2 and S3, which were etched for substantially longer time (40 and 80 min), were shifted towards 516 cm -1 . Since the change in the peak position of TO vibrational band can be attributed to the change in nanocrystallite size, 17 and to the change of the induced stress in the porous silicon layer due to the oxidation of material, 18 or to both, this may be an explanation for the observed oppositely directional shifts in samples etched in different time durations. Because of short etching time, the porosity of sample S1 was low, with small pore volume, so they behave like nanodefects.…”

“…The origin of the IR photoluminescence band is not completely understood, but several authors connected it with the point defects in porous material. 10,17,18,20 Figures 5a and 5b present the infrared photoluminescence spectra recorded, from the topside of epitaxial layer and from the top surface of substrate respectively, from oxidized samples stored in air for six month. Both images show that the most intensive PL is exhibited by the sample S1 which supports the assumption that its intensive photoluminescence is caused by the defects generated during oxidation process.…”