Measurement of strain and strain relaxation in free-standing Si membranes by convergent beam electron diffraction and finite element method

摘要

Bridge-shaped free-standing Si membranes (FSSM), strained by low-pressure (LP) Si_xN_y, plasma-enhanced (PE) Si_xN_y and Si_xGe_(1-x) stressors, were measured by convergent beam electron diffraction (CBED) and the finite element method (FEM). The results of CBED show that, while the strain along the length of the FSSM is compressive in an LPSi_xN_y/Si sample, those along the length of the FSSM are tensile in PESi_xN_y/Si and Si_xGe_(1-x)/Si samples. The average absolute values of strains are different in FSSM with LPSi_xN_y, PESi_xN_y and Si_xGe_(1-x) as stressors. The FEM was used to compensate the results of CBED taking into account the strain relaxation in transmission electron microscopy (TEM) sample preparation. The FEM results give the strain properties in three dimensions, and are in good agreement with the results of CBED. There is approximately no strain relaxation along the length of FSSM, and the elastic strains along the other two axes in FSSM are partially relaxed by thinning down for the preparation of TEM samples.