Mechanical stress relief in porous silicon free standing membranes

Romain Guider,Paolo Bettotti,Cristina Traversa

doi:10.1364/ome.5.002128

Abstract

In this work, we report on the difference of mechanical stress in free standing and attached Porous silicon membranes. By performing Raman analysis, we demonstrate that the tensile stress accumulated during the etching process by the porous silicon layer is partially compensated by the presence of the substrate. We highlight this complex effect by experimentally showing the balancing effect of the substrate and the change in mechanical stress between top and bottom surfaces in free standing membranes. In addition, this Raman investigation allows us to separate the effects on the Raman lineshape due to the nanostructures from those related with the mechanical stress of macroscopic structures.

Highlights

Porous silicon (PSi) has been investigated for decades for its peculiar optical and structural properties and the interest is far from fading out as demonstrated by its recent uses as sensor [1], thermoelectric [2] and photovoltaic device [3]
In this work, we report on the difference of mechanical stress in free standing and attached Porous silicon membranes
By performing Raman analysis, we demonstrate that the tensile stress accumulated during the etching process by the porous silicon layer is partially compensated by the presence of the substrate

Summary

Introduction

Porous silicon (PSi) has been investigated for decades for its peculiar optical and structural properties and the interest is far from fading out as demonstrated by its recent uses as sensor [1], thermoelectric [2] and photovoltaic device [3]. One of the main limitations to fully exploit nano-PSi capabilities is the fabrication of thick and mechanically robust FSMs. while it is rather easier to obtain thin films, membranes thicker than several tens of microns are difficult to handle as they tend to roll-up and crack because of mechanical stress accumulated during the etching. The authors correctly notice that the stress induced by the porosification of the semiconductor might produce a bending of the whole structure The releasing of the porous layer from the underlying substrate removes the nanocrystals as demonstrated by the disappearance of the PL signal), FSMs permit to decouple the quantum and mechanical effects and to obtain a direct and clean measure of the mechanical stress accumulated by the porous layers

Experimental details

Discussion

Conclusion