Deposition, examination and application of strain-compenstated layer structures in 3D MEMS

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Dr. Juhász László
Department of Electron Devices

Micro-Electro-Mechanical Systems, or MEMS, is a technology that in its most general form can be defined as miniaturized mechanical and electro-mechanical elements (devices and structures) that are made using micro fabrication techniques. Micro electromechanical systems are widely used in many detector or sensor types such as gas detectors or biological sensors. These micromechanical structures are suffering with many limitations including mechanical stress caused degradation or cracking. Strain-compensation is an optimization technique which helps to avoid these electro-mechanical elements from physical degradations or breakages and results increased lifetime as well as higher level reliability for the products. The process is based on the systematic change of the SixNy-SiO2-SixNy thin films thickness ratios.

The goal of my work was to develop a strain-compensated SixNy-SiO2-SixNy thin film structure for 3D MEMS application. During the designing process different models were built in a multi-physics simulation software (COMSOL) for studying the residual stress in thin films as well as the mechanical strain forces in complete devices.

Based on the results of the simulations, the optimal strain-compensated thin film ratios were determined and classification wafers were also created for the proving of the concept. Ellipsometry and Makyoh-topography classification analysis were carried out after the deposition process for the determination of oxide layer thickness and the wafer`s curvature radius. In the next phase a cantilever beam structure was evolved on the wafer`s surfaces. The deflection of the cantilever beam caused by residual stress was measured using total interferometry contrast (TIC) and scanning electron microscopy (SEM) techniques.

The results obtained with the different analytical techniques are also confirmed the simulation determined optimal thin film ratios. Finally, based on the obtained results of the current study and take into consideration results from literature, a motion was made for the development of an application which would allow the detection of single molecules using the optimized MEMS structures.


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