A Comparative Study of the Strength of Si, SiN and SiC used at Nanoscales
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A Comparative Study of the Strength of Si, SiN and SiC used at Nanoscales Tuncay Alan, and Pasqualina M. Sarro Electronic Components, Technology and Materials, Delft University of Technology, Delft, 2600GB, Netherlands
ABSTRACT Microelectromechanical systems (MEMS) are being used in many critical applications that require very high stress levels. To properly design MEMS components, mechanical properties should be characterized testing relevant sized samples that are fabricated with the same procedures as the final structure. In this paper we use atomic force microscopy (AFM) experiments to study the fracture strength statistics of polycrystalline SiC and SiN nanobeams, and compare their mechanical performance with the performance of previously tested Si nanostructures. Using the same AFM method and similar sample shape and sizes, allows a direct comparison to be made, which will be useful in determining the best material for different mechanical applications and also to validate the theoretical limits. INTRODUCTION Over the past decade, microsystem technology has attracted a significant commercial interest, and Microelectromechanical systems (MEMS) have been used in a wide variety of novel science and engineering products. At MEMS size scales the fracture properties of materials differ significantly from the well known bulk properties: They are influenced significantly by the sample size [1] and often by small changes in the fabrication processes [2] and by environmental effects [3]. So far, numerous studies (with novel in-situ experimental procedures) have been performed to characterize the mechanical properties and fracture reliability of materials used in MEMS size scales [4]. Yet, due to differences in experimental methods, geometric properties of the samples that were used and fabrication procedures, there is a significant scatter in the strength values reported by different groups. It is generally quite challenging to build the complex experimental set-ups that are required, which makes it difficult to repeat the tests performed by other groups. To generate a database of mechanical properties at small scales, and to effectively compare the properties of different materials, a test procedure that is easily repeatable (and not requiring a specially built equipment) is necessary. Here, we use atomic force microscopy (AFM) based bending tests [2,5] to compare fracture strength distribution of poly crystalline SiN and SiC samples with the strength of previously tested single crystal Si nanobeams. EXPERIMENT Sample Preparation The test samples were 200 nm thick doubly clamped beams that have an effective length of 5 µm and widths changing between 0.5 µm and 1 µm. The samples were fabricated using
standard lithography and wet etching procedures. A 200 nm thick layer of SiN or SiC was deposited on a (100) oriented Si wafer with low pressure chemical vapor deposition (LPCVD). The film was patterned through photolithography and the beam shape was defined in the deposited layer through dry etching. The d
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