Abstract
Polysilicon, which is vapor deposited, is by nature only a few microns thick. In typical MEMS applications, the structural features may also be only a few microns wide. Establishing the elastic and strength properties using specimens that are similar in size is quite a challenge. This paper describes a tensile test system that grips a large ‘paddle’ on the end of a tensile specimen with electrostatic force; this enables the testing of polysilicon specimens that have cross-sections as small as 1.5 × 2 microns. Polysilicon is a linear, brittle material and it is not difficult to measure its tensile strength, which is measured here to be on the order of 1.3 GPa. It is considerably more difficult to measure Young’s modulus, and two approaches are used here. In the first, strain is extracted from the force-displacement plot of the tensile test. The second uses two gold lines for laser interferometry to measure strain directly on the tensile specimen. Both approaches yield similar results, but the measured values are lower than the 169 GPa measured earlier on wider polysilicon specimens. Specimens 3.5 microns thick had a modulus of 142 ± 25 GPa, and those 1.5 microns thick showed 136 ± 14 Gpa. The techniques and procedures along with preliminary results are presented here.
