Abstract
An investigation of the influence of deposition and post-fabrication processes on the final mechanical structure of tantalum beams is reported in the present study. The final deflection profiles of doubly supported beams made from compressive and tensile-stressed films have been studied experimentally. An optimum finite element model has been developed to predict the buckling behaviour of the doubly supported beams by considering the boundary conditions in the form of a compressive stress and an applied load. No matter which etch release method has been used, the initial stress state of the as-deposited films has been found to have a significant impact on the final deflection profile of the fabricated device. The compressive-stressed films have presented larger deflection in the final released beams than the tensile-stressed films. Taking into account the type of etch release methods, the beams that have been released in the dry etch release processes have been found to deform more vertically than those released in the wet-etch release method. Moreover, it has been found that the amplitude of vertical deflection increases with the increase of the beam length and thickness. The results indicate that optimum profiles of tantalum suspended structures can be obtained from the tensile-stressed films that have been released by the wet etching method with an aspect ratio of 1:48.
Highlights
Microelectromechanical systems (MEMS) based devices such as membranes and beams have been used extensively in different application areas including pressure sensors [1,2,3], electrostatic actuators [4], and RF switches [5, 6]
The suspension of released structures has been confirmed by a scanning electron microscope (SEM), while the final deflection profile of the fabricated devices has been characterised by the white light interferometer (Zygo)
The unusual buckling profile that have been produced during the fabrication process cannot be fitted with the simple model that only takes into account of the compressive stress effect
Summary
Microelectromechanical systems (MEMS) based devices such as membranes and beams have been used extensively in different application areas including pressure sensors [1,2,3], electrostatic actuators [4], and RF switches [5, 6]. In order to obtain robust and reliable devices, the mechanical properties of structural metal beam should be improved by controlling the residual stress and etch release effects during the fabrication process. The deflection behaviour of structural metal materials such as tantalum has not been studied satisfactorily as much as the semiconductor processing materials such as Si, SiO2 and Poly-Si. The present study offers an investigation of the influence of post-fabrication process on the final mechanical structure of suspended tantalum beams. Compressive and tensile-stressed films have been sputtered on two types of sacrificial layers Both wet and dry etching techniques have been examined for the release of the final device in the form of doubly supported beams with length ranging from 100 to 400 μm. The final deflection profiles of the fabricated beams have been verified by creating several finite element models and analysing each model in terms of the compressive residual stress and external applied load. Further investigation has been performed to examine the influence of beam geometry, length, width and thickness, on the final deflection profile of the fabricated and simulated structures
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