Characterization of LPCVD amorphous silicon carbide (a-SiC) as material for electron transparent windows

Abstract

We investigate on the physical and chemical properties of non-stoichiometric amorphous silicon carbide (a-SiCx) thin layers deposited by low-pressure chemical vapor deposition (LPCVD). Characterizations are specifically tailored to understand the suitability of a-SiCx as electron transparent window material. The structure, composition, continuity, intrinsic stress, etch-rates and roughness of the layers are determined. The a-SiCx layers are highly uniform and continuous, showing tensile intrinsic stress and high chemical inertness. The layer with the lowest roughness (0.22 nm) and intrinsic stress (0.7 GPa) is employed to fabricate electron transparent windows of 16 nm for use in a Transmission Electron Microscope (TEM). The resulting windows are highly transparent, enabling the acquisition of TEM images down to the resolution limit of the microscope (0.12 nm). Moreover, the a-SiCx windows show a resistance to electron beam damage which is up to 9 times higher than that of the commonly employed low-stress LPCVD silicon nitride (SiNx). Therefore, the proposed a-SiCx is particularly suited for TEM experiments where high chemical inertness and/or long exposures to the TEM electron beam are required. In addition, the a-SiCx layer could advantageously be employed in the design of microelectromechanical systems (MEMS), especially those operating in harsh environments.