In-situ Measurement of Internal Stress in Electro Deposits by Television Holographic Interferometry

Abstract

Electro deposition technology has been utilized widely in various industries. However, the internal stress generated in the plated film during deposition often results in peeling and crack of the thin film. The investigation of generation mechanism of the internal stress is indispensable for improving the plating film. Measurements of internal stress are required during the early stages of film growth. In this study, TV holographic interferometry, which can capture holographic images at TV frame rates, was used to sensitively measure with the accuracy of λ/2 the deflection of the cantilever beam during the deposition on the substrate. Internal stress is calculated in-situ by substituting the deformation date in Stoney's equation. In this experiment, to examine the influence of the substrate on internal stress of electroplating, the epitaxial growth of plating was compared with the plating growth on an amorphous substrate. Next, internal stress was measured in various plating (Zn, Cu and Ni) without the additive. The generation mechanism of the internal stress was considered by the surface morphology (SEM) and the cross-sectional (TEM) observation of the plating film. The main results are as follows. 1) Internal stress during the early stage of film growth changes greatly on the surface of amorphous substrate compared with the epitaxial growth. But, the difference of both becomes small as the film grows up. 2) In general, internal stress rapidly changes in the initial stage of film growth, and changes gradually afterwards. 3) The compression stress is generated in Zn plating, the tensile stress is generated in Ni plating and in Cu plating, a tensile stress is generated in the initial stage of film growth, which immediately changes to compressive stress.