Residual stress modeling of density modulated silicon thin films using finite element analysis

Abstract

Density modulated thin films offer a compliant property that can reduce residual stress, which typically originate during the growth of thin films. Lower residual stress improves adhesion properties of the film with reduced buckling or delamination, and therefore leads to more durable coatings. In this study, finite element analysis (FEA) was employed to simulate the residual stresses developed in density modulated silicon (Si) thin films, which incorporate alternating low and high density layers. The main focus of this investigation is not developing new FEA algorithms but to verify the impact of density modulated layers quantitatively using computational methods. Hence, verification of a predicted stress reduction enhances the current understanding of the mechanics of density modulated layered thin films. FEA simulation results reveal that low density layers act compliant and result in significant reduction in film stress especially at the interface with the substrate. For example, maximum stress at the film/substrate interface, which is in the substrate, was reduced from 2897 MPa down to 2432 MPa by simply adding a 100 nm thick densitymodulated low-density Si layer in between a 300 lm thick Si wafer substrate and 1 lm thick conventional high density Si film, which makes the reduction percentage of the maximum stress about 16%. V

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“…FEA is a powerful tool to understand the characters of macroscopic structural materials, thus it has been widely introduced into analyzing thin film deformation and stress. [16,17] Compared with analytical modeling that cannot deal with nonuniform microstructure, FEA could achieve the numerical results for complicated systems and thus provide insight into their microscopic or submicroscopic mechanism.…”