Mechanical Parameter Extraction Using Resonant Structures
- PDF / 1,125,994 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 32 Downloads / 249 Views
MECHANICAL PARAMETER EXTRACTION USING RESONANT STRUCTURES J. Elders*, H.A.C. Tilmans*, S. Bouwstra** and M. Elwenspoek*, *MESA Research Institute, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands, **Mikroelektronik Centret, Building 345 east, DK-2800 Lyngby, Denmark ABSTRACT In order to model and design micromechanical sensors and actuators, it is of crucial importance that thin film mechanical parameters, such as the Young's modulus and the residual stress, are known. In this paper, the parameter extraction method using resonant structures has been used to obtain these data and has been compared with the bulge test. Circular aluminum diaphragms have been used as samples. INTRODUCTION Planar integrated circuit technology together with non-IC compatible processing steps such as wet anisotropic etching of silicon is used to fabricate microsensors, microactuators and microsystems. In order to model and design these sensors and actuators, it is of crucial importance that thin film mechanical parameters, such as the Young's modulus, and the residual stress are known. However, it is well known that thin film materials used in microsystem technology can have properties which differ from their bulk counterparts. Besides, thin films exhibit residual stress, which is strongly process dependent. This necessitates explicit
determination of the properties. In this paper, the resonance method will be highlighted using circular aluminum membranes. A similar measurement method has been presented in ref. [1] and ref. [2]. However, in this paper the resonance method is compared to the bulge test. Circular membranes are preferred because they are easier to interpret. The method can in principle generate the Young's modulus and the residual stress. The well known bulge test has been applied to the same aluminum membranes, allowing a comparison of the measurement methods. SAMPLE PREPARATION Silicon wafers were used as a substrate material for the aluminum deposition. Both sides of the wafer were covered with aluminum using a Varian (3117) E-beam evaporation system. The thickness of the films has been determined by breaking the samples and studying the interface with a Scanning Electron Microscope (SEM). The backside of the silicon wafer has been patterned using standard photolithographic techniques. The circular etch windows are defined by wet etching the aluminum in a 80% H3PO4 , 11% CH3 COOH, 4% HNO 3 , 5% H2 0 solution. Reactive Ion Etching (RIE) has subsequently been used to etch through the 380 Rm silicon wafer. Depending on the loading effect, the etch rate varied between 4 and 5 lam/min. at a pressure of 150 mTorr, a power of 100 Watt and an SF 6 / 02 gas mixture with flows of 50 sccm and 10 sccm respectively. The downward direction etched three times faster than the lateral direction.
Mat. Res. Soc. Symp. Proc. Vol. 308. ©1993 Materials Research Society
172
THEORY AND EXPERIMENTAL SET-UP Resonance mto
In principle, the Young's modulus and the residual stress can both be obtained from resonance data of
Data Loading...
