Mechanical property measurements of thin films using load-deflection of composite rectangular membranes

The internal stress and Young's modulus of thin films are determined by measuring the deflection versus pressure of rectangular membranes made of them. In order to reduce the measurement error for Young's modulus due to the unknown Poisson's ratio, a 2 mm × 8 mm rectangular membrane is adopted. Measurements are made by using a computerized measurement system. Low-pressure chemical vapor deposition (LPCVD) silicon nitride films are characterized and found to have an internal stress of 1.0 GPa and Young's moduls of 290 GPa, showing that the rectangular membrane load-deflection technique could be utilized to measure the internal stress and Young's modulus of films deposited onto LPCVD silicon nitride membranes. By using this composite membrane technique, a LPCVD polysilicon film and a plasma-CVD silicon nitride film are characterized. The internal stress and Young's modulus are found to be −0.18 GPa and 0.11 GPa for the LPCVD polysilicon film and 0.11 GPa and 210 GPa for the plasma-CVD silicon nitride film, respectively.