Abstract
In ULSI technology, MEMS devices, and wear-resisting coating, the films created a strong interest in mechanical properties. Several methods are used to measure the mechanical properties of thin films. Bulge test has a great virtue is that the relatively simplicity of the apparatus. Thus, we use bulge test to measure the mechanical property changes of Pt/Ti/SiNx and Pd/Ti/SiNx membranes induced by hydrogen.Based on exact solution described by Vlassak, the curve fitting method is used in the work to obtain a set of residual stress, initial height, and biaxial modulus. The specimen geometry has a tremendous influence on accuracy. Micromachining techniques using Si substrate apply to fabricate the bulge samples of free-standing substrate. The Michelson interferometry is used to measure the deflection of the membrane as pressure loading. In our works, bulge test experiment is preformed on SiNx, Pt/Ti/SiNx and Pd/Ti/SiNx films to obtain the curve of pressure versus deflection of center of the membrane. By curve fitting method, residual stress, biaxial modulus and initial height are acquired.The ambient gas are Ar, 5 % H2, 10 % H2, and 20 % H2. Varying H2 concentration, the residual stress and modulus of Pt/Ti/SiNx does not alter apparently. As H2 concentration increases, the residual stress of Pd/Ti/SiNx membrane abruptly decreases to minus values. Hydrogen adsorption in metals causes the volume expansion, and the SiNx restricts the metals. Thus, a significant initial height exists and residual stress has minus values. The elastic constant of Pd/Ti/SiNx membrane decreases as H2 concentration increases. While the elastic constant subtract effect of SiNx, minus values appear in 10 % H2, and 20 % H2. Whether the SiNx film interacts with hydrogen need to be concerned. The accuracy of the results from the data analysis needs further examination experimentally and theoretically.