BS EN 62047-8-2011 pdf download.Semiconductor devices Micro-electromechanical devices
Part 8: Strip bending test method for tensile property measurement of thin films.
It is recommended to perform a test under constant temperature and humidity. Temperature change can induce thermal drift during deflection measurement. The temperature change or thermal drift shall be checked before and after the test.
5 Test piece
5.1 General
The test piece shall be prepared by using the same fabrication process as the actual device fabrication, To minimize the size effect of a test piece, the structure and size of the test piece shall be similar to those of the device components.
There are many fabrication methods of the test piece depending on the applications. As an example, the fabrication of the test piece based on MEMS process is described in Annex B. A lot of strip bending test pieces can be fabricated on a die or a substrate.
5.2 Shape of test piece
The shape of test piece and symbols are given in Figure 1 and Table 1, respectively. The test piece shall be designed to minimize the bending moment effect. In order to minimize the effect, the maximum deflection shall be more than 40 times the thickness of the test piece, and the length of the test piece shall be more than 300 times the thickness of the test piece, and the width shall be more than 10 times the thickness of the test piece, and the length shall be 10 times larger than the width. The thickness of the substrate shall be more than 500 times that of the test piece. The dimension of the substrate is limited by the capacity of the test apparatus. The geometry of the fixed ends supporting the test piece can affect the test results. When etching the sacrificial layer and the supporting substrate of test pieces, the region beneath the test pieces can be over-etched, and this Is called by under-cut. The under-cut at the fixed ends shall be minimized (anisotropic etching would be desirable rather than isotropic etching).
6 Test procedure and analysis
6.1 General
a) The substrate containing test pieces is attached to a sample holder There are some recommendable methods for the sample attachment, such as magnetic attachment, electrostatic gripping, adhesive gluing, etc.
b) The translational and angular misalignment between the load tip and the test piece can affect the test results (refer to Figure C.2), and should be checked using an optical microscope. The misalignment error and the guideline for alignment are described in Annex C.
C) It is necessary to determine surface location of a test piece at the beginning of the test. The surface location is the position of the top surface of the test piece in the vertical direction when the strip deforms by the vertical movement of the load tip. This surface location can be determined by optical inspection using an optical microscope, or be determined by three successive indents. When the load tip touches the strip, the slight change in the strip configuration can be observed and identified using the optical microscope. The detailed method for determining the surface location using three successive indents is described in A.3.
d) The test is performed under a constant displacement rate until the strip ruptures. The displacement rate of LxlO’, or LxI0/s is recommended, which leads to the strain rate of approximately IxlO/x or lxlO4 c, respectively when the strain reaches 0,5 %. This method applies to strain rate insensitive materials since the strain rate changes during the test.
6.2 Data analysis
To obtain an actual force and deflection data of a test piece from the experimental results, several compensations may be required depending on the test apparatus. As an example, the data analysis procedures are described in Annex A for the case of a nanoindentation apparatus. These procedures can provide useful information for other types of apparatus. From the force and deflection measurements, stress and strain can be estimated by the following Equations (1) and (2). The equations are derived on the assumptions of negligible bending moment effect and uniform strain throughout the test piece [1-3]. See Figure 2.BS EN 62047-8-2011 pdf download.