Study and estimation of the residual stress in porous silicon layer formed on the surface of a crystalline silicon substrate

Stress control of porous silicon films for microelectromechanical systems

“…Using calculations as described earlier it was found that the internal stress of the PS changed from -2.0±0.02 MPa to 1.2±0.03 MPa (tensile) after annealing at 300 ˚C, and back to -1.9±0.01 MPa after the HF dip. This trend is consistent with previous reports of vacuum annealing and the effect of a HF dip on PS, attributed to surface hydrogen desorption and re-adsorption, respectively [5,20]. These results…”

Diffusion-Controlled Porous Crystalline Silicon Lithium Metal Batteries

“…Hence, just as Ghannam et al. (2008 ) illustrated by showing how the initial residual stress of the Si-film determines the ensuing pore-structure; herein, the top Si-surface porous layer (the denuded SC-PCS) maintains low residual stress, which permeates throughout the entire substrate during the anodization process, thereby resulting in a bulk structure with low-strain, highly compact PS.…”

“… Ghannam et al. (2008 ) were able to illustrate that the physical properties of Si-porosity strongly depend on the initial residual stress of the film, where the residual stress is directly related to both the initial pore radius and lateral strain acting on the surface of pores.…”

“…To circumvent this, composite materials including high-surface-area porous carbon ( Collins, 2014 ; Collins et al., 2018 , 2015 ; 2014 , 2013 ; Ferrari and Robertson, 2000 ), core-shell-type powder or slurry silicon additives ( Chae et al., 2020 ; Guo et al., 2017 ; Hu et al., 2008 ; Jia et al., 2018 ; Vrankovic et al., 2017 ; Wang et al., 2013 ; Xing et al., 2018 ; Xu et al., 2018 ; Zhai et al., 2017 ), or porous silicon (PS) ( An et al., 2019 ; Chen et al., 2019 ; Gardner et al., 2016 ; Ikonen et al., 2017 ; Jia et al., 2018 ; Karbassian, 2018 ; Lu et al., 2015b ; Xiao et al., 2015 ) have been in constant development. PS-based systems, in particular, yield opportunities for advanced control of Li-diffusion and plating processes through the manipulation of internal silicon-charge dynamics, where crystal structure can be formidably tuned by select surface functional groups ( Buttard et al., 1996 ; Ghannam et al., 2008 ; Sugiyama and Nittono, 1990 ) enabling enhancement of reversible electrochemical processes. Such surface-to-bulk structure/function relationships have been well elucidated via functional groups on high-surface-area carbon ( Collins, 2014 ; Collins et al., 2018 , 2015 , 2014 , 2013 ), thereby presenting an even greater opportunity for desired electrode performance when utilizing silicon with an additional filled π-orbital within Group 14 of the periodic table.…”

“…Recently, we have shown that when anodization is preceded by organic standard SC of the silicon substrate before etching, along with an additional SC after etching, the anodization process embeds a protective or ''lithiophilic'' (Liang et al, 2016;Zhang et al, 2018) interface on the silicon surface (Collins et al, 2020e;Souza et al, 2020aSouza et al, , 2020cSouza et al, 2020e). SC removes a majority of oxygen defect groups and replaces them with Si-H-terminated bonds, which produce an electrochemically protective lithiophilic nanoporous electrode, where the alteration of Si-O/Si-H surface functionality additionally increases the Si-Si crystallinity (Ghannam et al, 2008;Sun et al, 2014), compared with non-surface cleaned silicon wafer. Electrochemical anodization with surface cleaned p+ silicon wafers, therefore, has the potential to enable lithiophilic SC-PCS without any separation between porous and crystalline wafer components while seamlessly integrating the SC-PCS into patterned or planar wafer-level silicon (Collins et al, 2020e;Souza et al, 2020a;Souza et al, 2020e).…”