Microtensile testing of free-standing polysilicon fibers of various grain sizes

Abstract

Tensile strength and elastic modulus measurements of low-pressure chemical vapour deposited (LPCVD) polysilicon films were performed on freestanding microtensile specimens (fibers) fabricated from the films. Various annealing treatments were employed to alter the polysilicon grain size. Fibers were fabricated from films with grain sizes of 50, 100, and 500 nm. The fiber cross sectional area was 3.3 mu m3 and the gauge section was 30 mu m long. The fibers failed in a brittle fashion with tensile strengths between 2.7 and 3.4 GPa. Fibers fabricated from polysilicon with 500 nm grain size had uniform equiaxial grains and were stronger than fibers made from smaller grain size material. This higher strength can be attributed to the better interface between the 500 nm grains as a result of the annealing process. The average elastic modulus of the fibers was 175 GPa.

A new microtensile tester for the study of MEMS materials with the aid of atomic force microscopy

“…Of the aforementioned techniques, tensile tests 1−8 are less vulnerable to geometry-induced errors and the measurements are easier to interpret from an error analysis point of view. Tensile tests have been performed using electrostatic gripping of specimens, 6 adhesive media, 5 or micromanipulators 4 with specially designed specimens, either in a scanning electron microscope (SEM), 4−6 or interferometrically 3 to measure relative displacements.…”

Standalone Tensile Testing of Thin Film Materials for MEMS/NEMS Applications

“…The early efforts in the tensile testing of thin films were the concurrent research work of Ruud et al, 1993, Koskinen et al, 1993, and Read & Dally, 1993 in the early 1990's. Ruud et al, 1993 introduced a tensile testing technique to test free standing thin film specimens with gage section area of 10 mm long by 3.3 mm wide.…”

“…With this technique, they managed to determine the Young's modulus, Poisson's ratio, and yield strength of free-standing Cu, Ag, and Ni films (Ruud et al, 1993) and Ag/Cu multilayers (Huang & Spaepen, 2000), and to study the yield strength (Yu & Spaepen, 2004) and anelastic behavior (Yu, 2003) of thin Cu films on Kapton substrate. Koskinen et al, 1993 used a relatively simple technique to test LPCVD polysilicon films. They introduced a gripping setup that could hold an array of 20 samples and was capable of loading individual specimens.…”

Influence of Grain Structure and Doping on the Deformation and Fracture of Polycrystalline Silicon for MEMS and NEMS

“…Given its granular microstructure, the strength of polycrystalline silicon is limited in an even smaller range of 1-5 GPa [5][6][7][8][9][10]. In both cases, the mechanical strength is dependent on specimen size [2,8,11].…”