Measurement of Internal Stress in Thin Films.

摘要

A description is given of a device used to measure internal stresses in thin films vapor deposited on cantilevered beam substrates. The stress-induced deflection of a substrate used as the electrode of a capacitor causes a shift in the null of a capacitance bridge. A tuuned amplifier is used to detect the shift in capacitance null indicating the value of the stress in the film. Our circuitry provides a resolution of 0.02 picofarad which results in a stress sensitivity for our apparatus of 5 x 10 to the 7th power dynes/sq. cm. This enabled us to determine stress in a .001 A film of amorphous germanium to within 5%. Inexpensive integrated circuits are used to generate and process the ac signal.