Intrinsic stress, mismatch strain, and self-assembly during deposition of thin films subjected to an externally applied force

Abstract

A relation is derived between the mismatch strain, the film thickness, and the displacement of a linear elastic structure under external loading during material deposition. If any two of these variables can be experimentally determined, then the remaining variable can be determined. The method allows one to experimentally determine the mismatch strain by measuring the film thickness and the displacement of a point on the structure that is not undergoing deposition. The intrinsic stresses can be used to self-assemble microstructures during material deposition. Assembly of two components is considered: one component is subjected to deposition and is modeled as an Euler-Bernoulli beam, and the other component is not subjected to deposition and is modeled as a linear spring. For the purposes of this paper, the definition of assembly requires that the beam do work on the spring. The analysis is experimentally verified by electroplating nickel onto an AFM cantilever beam in contact with a second AFM beam (serving as the spring) that does not undergo deposition.

Sensitivity analysis of plating conditions on mechanical properties of thin film for MEMS applications

“…The step profiler method also induces the mechanical contact between the probe and the micromachined structures, which may lead to some unwanted effects such as friction during the measurement. Recently the resonance method has been used to measure the mechanical properties of electroplated thin films [10,11]. Young's modulus and residual stresses of the fabricated beam structures were determined by detecting the resonant frequencies of microbeams, which is a useful method to measure the thin film properties because of its well defined analysis theory.…”