Temperature-Dependent Coefficient of Thermal Expansion of Silicon Nitride Films Used in Microelectromechanical Systems
- PDF / 1,173,191 Bytes
- 6 Pages / 411.12 x 635.4 pts Page_size
- 77 Downloads / 236 Views
ABSTRACT Microelectromechanical systems (MEMS) have potential application in high temperature environments such as in thermal processing of microelectronics. The MEMS designs require an accurate knowledge of the temperature dependent thermomechanical properties of the materials. Techniques used at room temperature often cannot be used for high-temperature property measurements. MEMS test structures have been developed in conjunction with a novel imaging apparatus designed to measure either the modulus of elasticity or thermal expansion coefficient of thin films at high temperatures. The MEMS test structure is the common bi-layered cantilever beam which undergoes thermally induced deflection at high temperatures. An individual cantilever beam on the order of 100 ýtm long can be viewed up to approximately 800 0 C. With image analysis, the curvature of the beam can be determined; and then the difference in coefficient of thermal expansion between the two layers can be determined using numerical modeling. The results of studying silicon nitride films on silicon oxide are presented for a range of temperatures. INTRODUCTION There are numerous applications for MEMS structures, in the microelectronics industry. Complete knowledge of the thermophysical properties of the materials used in such structures is
essential in successful production of microchips. Although the thermophysical properties for the materials used in the microelectronics industry are known for bulk values, properties for thin films of the same materials are different and essentially uninvestigated at high temperatures. If thermophysical property differences between thin film and bulk materials are not taken into account during processing, a failed structure will most likely result. Current techniques used to measure thermophysical properties in bulk samples at high temperatures cannot be applied to measuring properties in thin films - the structures are simply too small or nearby equipment gets too hot. Thus, there is a lack of information with respect to thermophysical properties of thin film materials at high temperatures. The development of new techniques to measure the properties of such materials is imperative for proper processing. Two important thermophysical material properties that must be known for thin film fabrication are Young's modulus (E) and the coefficient of thermal expansion (ax). One test structure that has been used to investigate mechanical material properties of thin films is a microscale bi-layered cantilever beam structure (see Figure 1) [1]. The technique commonly used to determine Young's modulus for such materials involves finding the resonance frequency of such a structure. Buchaillot et.al [1] and Hoummady et.al [2] have conducted such studies at room temperature.
+Author to whom all correspondence should be addressed
235 Mat. Res. Soc. Symp. Proc. Vol. 605 ©2000 Materials Research Society
Figure 1. Microscale Bi-layered Cantilever Beam Structure To the best of the authors' knowledge, very little research has been conduc
Data Loading...
