In transmission electron microscopy (TEM), silicon nitride (SiN) films are widely used as sample-supporting films owing to their robustness. We fabricated large-scale SiN films deposited by low-pressure chemical vapor deposition (LPCVD). This preparation method is advantageous for large window areas, since it yields films with control over properties such as tension and thickness. We fabricated large SiN windows for mounting large ultrathin sections and for acquiring large-area TEM images. Thus, sample sections sliced by conventional sample preparation techniques were successfully mounted on these sample-supporting films. We successfully obtained a 680 × 250 μm2 TEM montage image of a whole Drosophila embryo.